star formation

Where do Rogue Planets come from?

esiegel — Wed, 11 Sep 2013 15:37:51 +0000

Where do Rogue Planets come from?

"Like all animals, human beings have always taken what they want from nature. But we are the rogue species. We are unique in our ability to use resources on a scale and at a speed that our fellow species can't." -Edward Burtynsky

It's really a romantic notion when you think about it: the heavens, the Milky Way, is lined with hundreds of billions of stars, each with their own unique and varied solar systems.

Image credit: 湖北直行便 of AstroArts, via http://www.astroarts.jp/photo-gallery/photo/13870.html.

But beyond that -- in addition to the stars -- there are hundreds of billions of planets with no central stars at all: the rogue planets of our galaxy. We think this is true everywhere, from small star clusters to giant galaxies. As best as we can tell, there are at least as many starless planets wandering the cosmos as there are stars, meaning that for every point of light you see, there are probably more massive points that exist, but emit no visible light of their own.

Image credit: Southwest Research Institute.

We've recently discovered a number of possible rogue planet candidates, although since these are so difficult to detect (and are only visible from their heat signatures in the infrared) we know that there must be many, many more than what we've seen so far. You can't help but wonder where these rogue planets come from!

One compelling source is near and dear to us all.

Image credit: Axel M. Quetz (MPIA).

We know how solar systems like our own form: you get a central star with a protoplanetary disk around it. Gravitational perturbations in the disk attract more and more matter from their surroundings, while the heat from the newly formed central star gradually blows much of the lightest gas away into the interstellar medium. Over time, these gravitational perturbations grow into asteroids, rocky planets, and eventually -- for the largest ones -- gas giants.

Image credit: NASA / JPL-Caltech.

The thing is, these worlds don't just orbit their central star, they also gravitationally tug on one another! Over time, these planets migrate into the most stable configurations they can attain, and this usually mean the largest, most massive worlds migrating into their most stable configurations, often at the expense of other worlds.

A recent simulation shows that for every planet-rich solar system like our own (with gas giants) that forms, there's likely to be at least one gas giant planet that gets kicked out, into the interstellar medium, where it's doomed to wander the galaxy on its own as a rogue planet.

Image credit: NASA / JPL-Caltech.

That's almost definitely a major source of rogue planets.

But here's the funny thing: when we work out the numbers of our best theoretical calculations, it's far less than 50% of all rogue planets that are expected to be accounted for by this process. To figure out where the majority of starless planets come from, we have to look at a larger scale at around the same time: not just when the Solar System formed, but at the cluster of stars (and star systems) that all formed at around the same time!

Image credit: ESO / R. Chini, from the ESO's Very Large Telescope.

Star clusters form from the slow collapse of cold, mostly hydrogen gas, typically within a galaxy. Within these collapsing clouds, gravitational instabilities form, and the earliest, most massive instabilities preferentially attract more and more matter. When enough matter gets together, and the densities and temperatures at the core of these clouds get high enough, nuclear fusion ignites!

Image credit: Joseph Brimacombe.

This results in new stars and star systems, but something else happens, too. The biggest stars that form are also the hottest and bluest, meaning they emit the most ionizing, ultraviolet radiation.

So when you look inside a star-forming nebula in the Universe, you are actually watching two processes simultaneously competing:

Gravity, as it attempts to pull matter in towards these young, growing gravitational overdensities, and
Radiation, as it works to burn off the neutral gas and blow it back into the interstellar medium.

Who will win?

Image credit: Sid Leach of the Eagle Nebula, via http://www.sidleach.com/m16.htm.

It depends what you mean by "win," exactly. The biggest gravitational overdensities form the largest stars, but these are also the rarest of all stars. Smaller (but still large) ones form the other star types, but become more and more common as we get down to lower masses. This is why, when we look deep inside a young star cluster, it's easiest to see the brightest (blue) stars, but they're vastly outnumbered by lower mass, yellow (and especially red), dim stars.

Image credit: Sloan Digital Sky Survey, of Messier 67.

The thing is, if it weren't for the radiation, there dim, red-and-yellow stars would have grown more massive, brighter, and burned hotter! Stars (on the main sequence, which is most stars) come in a variety of types, O-stars being the hottest, largest and bluest and M-stars being the coolest, smallest, reddest and least massive.

Image credit: Wikipedia user Kieff.

Even though the vast majority of stars -- 3 out of every 4 -- are M-class stars, compared to less than 1% of all stars being O-or-B stars, there's just as much total mass in O-and-B-stars as there are in M-stars.

And it turns out that some 90% of the original gas-and-dust that was in these star-forming nebula gets blown off back into the interstellar medium rather than forming stars. The most massive stars form the fastest, and then get to work blowing the star-forming material out of the nebula. By time a few million years go by, there's less and less material to form new stars at all. Eventually, all the leftover gas-and-dust will burn off completely.

Image credit: NASA and The Hubble Heritage Team (STScI/AURA).

Well, guess what? Not only are M-class stars -- stars between 8% and 40% of the Sun's mass -- the most common type of star in the Universe by far, but there are a whole lot more that would have been M-class stars if it weren't for the high-mass stars burning off this material!

In other words, for every star that forms, there are many, many failed stars that didn't quite make it; anywhere from tens to hundreds-of-thousands of them for each star that actually forms!

Image credit: Greg Stewart / SLAC National Accelerator Laboratory.

These nomad planets -- or rogue planets -- may or may not have atmospheres, and they may be incredibly difficult to detect, especially the (theoretically) more common ones: the smallest objects.

So we may have a few rogue planets that were ejected from young solar systems, and there may even be a couple that came from our Solar System, but the vast majority were never attached to stars at all! Rogue planets wander the galaxy, most of them to toil forever in loneliness, never knowing the warmth of a parent star, thwarted by stellar evolution from ever becoming stars themselves. What we have, instead, is a galaxy with trillions or possibly even quadrillions of these nomad worlds, objects which we're only just beginning to discover. And that's where rogue planets come from!

esiegel Wed, 09/11/2013 - 11:37

Tags

Astronomy

gravity

Physics

Solar System

So are the masses of the Roque Planets taken into account in the tally of the mass of the Universe ? Are they part of the 4 % ? What is the best estimate for the mass difference between "trillions " and "quadrillions" ? Thanks.

Is there a reason for the power law that says that each class of stars has roughly the same total mass? It seems unlikely to be coincidence, yet there doesn't appear to be any obvious reason why there should should be any scaling law, let alone one that is so orderly.

In the hypothetical case of a gas giant booted out of its orbit by Jupiter, why is it so obvious that it would be totally expelled from the solar system? Couldn't it still remain in a very distant orbit?

Wow! Like using exclamation points, much!

Yes, a gas giant thrown into the far reaches of the solar system can get stuck there (identical to how we produce Oort cloud comets), but the chance of that happening is only a couple percent. So - probably not, unless there were dozens.

@ 1

The mass of any rogue planet compared to 1 solar mass is extremely tiny. Given a galaxy you might at best get 0.1% contribution. And yes, they are in 4% part since they are made of matter like everything else.

@2
yes, you can check stellar classification. Basically it's like black body radiation. Different colors, different temperatures hence energies, hence composition, hence mass needed to produce such and such radiation.

SL, re answer to #1, it would be more complete and helpful to say that it is part of the 4% because it will, despite being "dark", it interacts with normal matter and can be captured like normal matter. It is also able, since it is a coalesced body of significant size, be able to spot a significant portion by their occlusion of starlight.

True Dark Matter (tm) doesn't interact even with itself well and therefore doesn't coalesce and, if it reacted with photons (the idea is it would not, any more than it would with normal matter, but if it did, it would be pushed out of every stellar envelope by photon pressure), it is a diffuse body and does not cause extinction in the same way.

And like Velikovsky said, when a HUGE object (we are calling them rogue planets here) comes into the influence of a star, it becomes a comet. As Jim McCanney says, the object then discharges the Solar Capacitor like a bug zapper. This causes the Sun to begin to increase its activity. The bigger the object, the more the solar activity. We do not see HUGE comets the size of Venus too often, luckily, but we have had them pass nearby on occasion. They are usually very destructive and can account for massive Earth changes simply by passing near by, without impact. Like Velikovsky proposes, Venus was a comet before it fell into its present orbit. It happened in recorded history and caused people to go underground at the time it passed by us, possibly 4K years ago. Venus even exhibited a tail.

@ Wow

Well, I did say it :) "And yes, they are in 4% part since they are made of matter like everything else."

you must have missed it.

@3: It's possible for a planet to be kicked into an orbit which is highly elliptical but still bound. To do that, you would have to boost its speed to somewhere between the circular orbit speed and escape speed for its previous location. IIRC, these two speeds differ by a factor of sqrt(2). The problem is whether such a planet would remain in that orbit without having nasty effects on the planets remaining in more conventional orbits whenever this planet approaches periastron. Near apastron, it wouldn't take much of a gravitational kick from a nearby star to turn this planet into an Oort cloud object (similar to how Oort cloud objects become comets), or finish the job of kicking it out of the solar system. Alternatively, the remaining planets could finish the job when this planet next approaches periastron.

No, you said it but it was implied, not explicit.

All you said in explicit form was "it's not like dark matter because it's like the regular matter".

You never explained why it would be known to be part of the 4% of normal matter and not part of the 20-ish% of dark.

Just said it wasn't.

true, it was implied, because Ethan's article is about it. Since they are made of the stuff that was in our solar system.

Didn't think @1 was asking if they were DM, rather if their mass contribution was accounted for in normal matter. Guess it's how you interpret the question. Anyways you added more to the answer so it's all cool :)

"Since they are made of the stuff that was in our solar system. "

sorry.. should be our/other solar system.. hence hydrogen, rocks, metals etc...or just gas giants

"Didn’t think @1 was asking if they were DM,"

That's how I read it.

Use the term rogue planet and the cranks come running in, as displayed by wally58 above.

I believe the theoretical argument that they should form, but what direct observation is there that they do form?

@16

not likely to get "direct observation" any time soon. Think about it. How do you observe a tiny speck that doesn't emit light.. hence black.. against a black background of space?

It will be a major breakthrough when we get to "directly observe" any planet outside of our solar system. Those wandering the blackness of space.. who knows.. maybe in some other bands if they emit something.

"How do you observe a tiny speck that doesn’t emit light.. hence black.. against a black background of space?"

I'm reminded of the conversation aboard Hot Black Desiato's ship with this...

I believe a few months ago we have the first direct observation of an extrasolar planet.

Though that might have been the observation of the absorption spectra of a planetary atmosphere (dense enough neutral matter to be neither space dust nor stellar atmosphere).

@Wow #19: Direct observation of extrasolar planets goes back several years, to at least 2004. HR8799's four planets were imaged back in 2010; AB Pictoris has a companion which is either a brown dwarf or Jovian-mass planet, directly imaged in 2003. See http://en.wikipedia.org/wiki/List_of_directly_imaged_extrasolar_planets for a current list.

Thank you Michael! This is awesome. To this day I wasn't aware that this was done.

Read the paper on GJ 504. Awesome! A real image of a planet orbiting some other sun. So cool!

p.s. Ethan, why no article on that we are actually able to image exoplanets?? :D Bad Ethan!! :))

Well, I remembered a story a few months ago (earlier this year anyway) and may have been about the direct measuring of the atmosphere of the planet rather than imaging the planet directly.

Rogue planets came from bad family backgrounds?

@Wow #23: Ah! I think you're remembering the recent spectroscopic analysis of HD 189733b (http://en.wikipedia.org/wiki/HD_189733_b).

A study of the combination of absorption features derived for the planet from secondary eclispes allowed the authors to "estimate" the apparent color the planet would have if we could see it directly.

No exoplanet has yet been imaged in "true color," although, given the progress in the field, that is only a matter of time.

Probably is, Mike.

Everyone: ferocious criticism invited for the following:

Are there any estimates of (or any reasonable basis for estimating) the occurrence of approximately-Earth-mass rocky rogue planets?

Those might be useful for interstellar colonization as follows:

1) Locate Earth-sized rogue planet.
2) Build Dyson rings around two or more of its nearest suitable stars.
3) The Dyson rings capture energy from the stars and convert to microwave laser or similar means, directed toward artificial moons (or captured space rocks with infrastructure built) orbiting the rogue planet.
4) At the moons, incoming energy is converted to a form that can safely be beamed down to the planet's surface and used.
5) Meanwhile, the Dyson rings are inhabited by minimal populations needed to maintain them. These should be small enough populations as to easily migrate off the Dyson rings to the client planet when the stars became hazardous toward the end of their useful lives.

Why go through all that effort, when there are Earth-sized planets orbiting stars, that can be colonized?

Because then you have an inhabitable world that is not a) dependent on and b) at risk from, a single star. Its usable lifespan would be equal to the useful life of the most long-lived of the stars that provided it with energy. Assuming you need at minimum two stars to supply energy to a rogue planet, build Dyson rings around a total of three or more stars, and you have time to replace any of them that are lost in stellar explosions.

Also it would seem that rogue planets in and of themselves, could potentially have the raw materials needed to support life, but be lifeless due to lack of energy sources. Thus they are ready to colonize with zero to minimal risk of encountering indigenous microbes that could prove fatal.

Comments?

G: even for sci-fi, your proposal is extremely Rube Goldberg-ish. Any civilization that can do step 2 has no need of any of the other steps; it can simply move to another system when the old star is close to burning out.

Secondly, wouldn't it just be easier to locate a rogue planet with some internal heat associated with it, and just use that? Whether gas giant or rocky, the rogue planet's gravitational force on its own mass will tend to heat things up at depth. I have to think that extracting that heat as work must be a great deal easier than your set-up. A jupiter-sized geothermal generator is (speculatively) peanuts compared to ringworlds firing interstellar lasers.

Messier Monday: The Triangulum Galaxy, M33

esiegel — Mon, 25 Feb 2013 17:23:55 +0000

Messier Monday: The Triangulum Galaxy, M33

"Let the great world spin for ever down the ringing grooves of change." -Alfred Lord Tennyson

Welcome back, for another Messier Monday here on Starts With A Bang! Each Monday, we've been taking a look at one of the 110 Deep-Sky Objects that make up the Messier catalogue, a mix of clusters, nebulae, galaxies and more, all visible from most locations on Earth with even the most basic of astronomical equipment.

Image credit: Greg Scheckler, from his 2008 Messier marathon, where he nabbed 105/110.

When you think of our local group of galaxies, you probably think of the Milky Way and Andromeda, and then "everything else" as an afterthought. I can hardly blame you for that; at only 2.5 million light years, it's the biggest, brightest extended object in the night sky. With an estimated one trillion stars, it's the biggest galaxy in our neighborhood, followed by the Milky Way at number 2.

But did you ever wonder what the third largest galaxy in our neighborhood is?

Image credit: DoomWillFindYou of deviantART.

Believe it or not, there's another galaxy within our local group that's actually (barely) visible to the naked eye: the Triangulum Galaxy, also known as Messier 33. Here's how to find it, but only on nights where there's low light pollution. (I.e., not tonight, when there's a full moon!)

Image credit: me, using the free software Stellarium, from http://stellarium.org/.

Early in the night, the bright clusters Hyades (highlighted by Aldebaran) and Pleiades are prominent, with Jupiter presently between the two. If you draw an imaginary line connecting Aldebaran to the Pleiades and continue, it will take you across the sky towards the bright star Mirach (in the constellation of Andromeda), not so far away from the bright "pair" Hamal and Sheratan (in Aries).

Image credit: me, using the free software Stellarium, from http://stellarium.org/.

But the small constellation Triangulum is found in there, and practically midway between the Hamal/Sheratan pair and Mirach is a very faint object just barely visible to the naked eye. It's the only Messier object in this constellation, and whether you can see it or not is a great test of how dark your skies are.

Image credit: Bortle Dark-Sky Scale, generated with Stellarium.

In skies darker than the suburban/rural transition (a "4" or lower on the Bortle scale), you've got a great shot at finding it! Through a good pair of astronomy binoculars, a small "ring" of five stars appears to encircle this deep-sky object, and -- although it will be mind-numbingly faint -- you'll never forget it if it appears for you.

Image credit: me, using the free software Stellarium, from http://stellarium.org/.

Why's that? This is a real "small wonder" of a galaxy. With just 40 billion stars, it's only 10% as massive as our Milky Way, but appears as the second-brightest galaxy in the sky because it's so close! At just 2.8 million light-years distant and inclined at 54° to our line-of-sight, it gives us the best "face-on" view of any close galaxy!

Image credit: Astrophotography by Alson Wong, http://www.alsonwongastro.com/.

The only drawback is that it's so close that low-magnification viewing is practically a necessity! But if you build up your observations over long enough time periods, you can develop a clear, spectacular view of our next-door neighbor!

Image credit: Robert Gendler of http://www.robgendlerastropics.com/.

Because it's so close, we've not only seen some spectacular views of M33, we've also learned a ridiculous amount about astronomy from it. There are the red areas, which are indicative of star-forming, ionized regions of space, sweeping spiral arms, along with billions and billions of stars.

Image credit: Robert Gendler, Subaru Telescope (NAOJ).

The many variable stars in this galaxy are well-studied enough that our figure of 2.8 million light-years is pretty robust for its distance.

Image credit: Paul Mortfield, Stefano Cancelli.

You may also notice that one of the reddish regions is absolutely huge! This region is known as NGC 604, and it is the largest, brightest star-forming region in the entire local group!

Image credit: ESA/Hubble and NASA.

It's over 40 times as large and 6000 times as bright as the Orion Nebula, with about 200 prime candidates for a spectacular Type II supernova! If this star-forming region were located in our neighborhood of the Milky Way, it would outshine every star and planet in the night sky.

Image credit: H. Yang (UIUC), HST, NASA.

But -- as is often the case -- there's a ton to be learned from looking in a multitude of wavelengths.

Image credit: John Corban & the ESA/ESO/NASA Photoshop FITS Liberator.

From the visible light images, we learn that there's practically no bar in the center of this galaxy, and from the motions of individual stars, we also learn that there's no supermassive black hole in there, either. In fact, if there is a massive black hole, it's less than ~~three thousand~~ 1,500 solar masses, whereas supermassive black holes normally range from a few million to many billions of solar masses.

But there are some amazing things happening.

Image credit: NASA/JPL-Caltech, Spitzer Space Telescope.

The Spitzer Space Telescope shows us this galaxy in the infrared, and highlights extended dust far past where the spiral arms are. Reconstruction of faint IR signatures shows that there was once a gravitational encounter between M33 and the great Andromeda galaxy, and we now think that ourselves, Andromeda and the Triangulum galaxy will all eventually merge together, with the most probable outcome being a merger of Andromeda and the Triangulum galaxy maybe a billion or two years before the Milky Way-Andromeda merger we're all looking forward to.

Image credit: GALEX / NASA / JPL-Caltech.

This Ultraviolet view, from GALEX, shows the location of bright, young blue stars, which the Triangulum Galaxy is full of! The spiral arms are clearly traced out in the Ultraviolet, but the central "bulge" that we're so familiar with in our own galaxy seems absent.

In fact, there is no central bulge in this galaxy, but something fishy is happening in there. And that's something we only know thanks to our X-ray eyes.

Image credit: XMM-Newton / EPIC Colo(u)r.

There's an ultra-luminous X-ray source coming from the center of the Triangulum galaxy, which is the most luminous X-ray source in the entire local group! This sort of X-ray source very close to the center of a galaxy is thought to be extremely rare, and yet, out of the three major galaxies in our local group, there it is.

Unlikely events happen all the time in the Universe, and we have the chance to enjoy one right here in our own backyard.

Image credit: © Oriol Lehmkuhl and Ivette Rodríguez of http://astrosurf.com/.

So look for the Triangulum Galaxy, Messier 33, the next time the skies allow it, and now you know what you'll be seeing!

Including today, we’ve taken a look at the following Messier objects:

M1, The Crab Nebula: October 22, 2012
M8, The Lagoon Nebula: November 5, 2012
M13, The Great Globular Cluster in Hercules: December 31, 2012
M15, An Ancient Globular Cluster: November 12, 2012
M30, A Straggling Globular Cluster: November 26, 2012
M33, The Triangulum Galaxy: February 25, 2013
M37, A Rich Open Star Cluster: December 3, 2012
M41, The Dog Star’s Secret Neighbor: January 7, 2013
M44, The Beehive Cluster / Praesepe: December 24, 2012
M45, The Pleiades: October 29, 2012
M48, A Lost-and-Found Star Cluster: February 11, 2013
M53, The Most Northern Galactic Globular: February 18, 2013
M60, The Gateway Galaxy to Virgo: February 4, 2013
M67, Messier’s Oldest Open Cluster: January 14, 2013
M78, A Reflection Nebula: December 10, 2012
M81, Bode’s Galaxy: November 19, 2012
M83, The Southern Pinwheel Galaxy, January 21, 2013
M97, The Owl Nebula, January 28, 2013
M102, A Great Galactic Controversy: December 17, 2012

Come back next week for another Messier Monday, where we'll spotlight our twentieth Messier object since we started this series! And for those of you who want some fantastic international news, Starts With A Bang fan Olaf van Kooten has begun translating our Messier Mondays into Dutch over at astroblogs.nl, because the joys and wonders of the Universe should be freely available for everyone to enjoy!

esiegel Mon, 02/25/2013 - 12:23

Tags

Great post and now it's in Dutch too! Wahoo. I love Mondays.

from the motions of individual stars, we also learn that there’s no supermassive black hole in there

It makes sense that large galaxies would have an SMBH at the center, and sufficiently small galaxies would (probably) not. But does anyone know how steep the transition curve is? IOW, is there some particular galaxy mass at which the probability of finding a SMBH jumps from near 0 to near 1, or is that spread out over a range of masses?

The thing to remember about M33 is that the damn thing is invisible.

Really, the surface brightness is so dim you can't see a sodding thing and the AFOV of anything wide enough to gather a fair bit of light in is so small that your field of view is filled by the galaxy and can't see the edge because of that.

Lovely photographic object.

Complete pants for visual work.

May the lack of a SMBH be related to the lack of a central bulge? I believe bulge-less spirals are thought to have experienced less major mergers. Perhaps less mergers also mean a less massieve central black hole?

But I have another question. Spiral galaxies are believed to have formed from many smaller galaxies. But can (some) spiral galaxies have formed "as is"? I'm asking this, because of the galaxy NGC 2915.

In visible light it's just a normal dwarf galaxy (http://www.astroblogs.nl/wp-content/uploads/2013/01/ngc2915-optisch-500…), however, when you map the neutral hydrogen around this galaxy, suddenly a M33'esque spiral galaxy appears (http://www.astroblogs.nl/2013/01/20/bijzondere-sterrenstelsels-deel-1-h…). Because of the isolated nature of NGC 2915 this gas has yet to collapse into stars, but when it happens, may a spiral galaxy reminiscient of M33 be the end result?

So if there's no black hole, is there a giant star-like furnace at the center of the galaxy?

A star-like furnace? What do you mean?

I love the Triangulum.

"See that line of three stars, with the four around it, and that arc over there? To me it looks like Orion, the great hunter!"
"Ah, I see it! And those stars there that form a cross, doesn't it look like a swan with it's wings spread and neck extended?"
"Oh yes, how beautiful. What about you, Biggus, what do you see?"
"Well... you see those three stars up there?"
"Yeah?"
"Well to me they sorta look like... a triangle."
"..."

What is causing the x-ray source?

Although the actual constellation IS possible to tell from "three stars make a triangle", since the Greek derivation of the name is basically Delta. Which has one fat side when written in script, and the triangulum constellation has (IIRC) three stars at one corner making a sort of sharp bend. As if it were written in scrip with a quill pen.

There are plenty other REALLY STUPID constellations out there.

Aries. Yeah, totally looks like a ram...
Pisces. Uh, you mean a long V with a circle of stars on the end of one of them? And that's supposed to be fish???

On a few, the author really acknowledges that this is all bunkum. Lynx is down as being there by the creator of it "I needed something in that large gap of naff all between the other constellations".

Some are odd (as in don't actually make what they say). Hell I suppose most have that problem, but are still unique and recognisable.

Triangulum, though binoculars especially, is one.

Um yes, obviously Triangulum wins the "Constellation or Asterism That Looks Most Like What It's Called" contest. Not even the Big Dipper has a chance against it.

That's my whole point. Of all the constellations named with imagination and poetic metaphor (and perhaps pharmaceutical enhancement), the namers of Triangulum went for on-the-nose literalism. Sure it's unique and recognizable -- if you know what triangles don't count because they're parts of other constellations. If that's the ideal, let's rename Lyra as "parallelogram plus bright star".

But why stick to cold geometric names when there's no actual physical significance to the arrangement? The poetic names are just fine. Sure Aries doesn't look like a ram, and it takes a fair bit of imagination to see a pair of fish on a rope in Pisces, but so what? You don't learn the constellations by going outside with nothing but a list of the names and guessing based on resemblance.

From my point of view even Lynx is better because sure it's arbitrary but who cares, it at least sticks with the theme of metaphorical representation.

The Evolution of Starlight

esiegel — Wed, 16 Jan 2013 16:43:25 +0000

The Evolution of Starlight

“Aristotle taught that stars are made of a different matter than the four earthly elements— a quintessence— that also happens to be what the human psyche is made of. Which is why man’s spirit corresponds to the stars. Perhaps that’s not a very scientific view, but I do like the idea that there’s a little starlight in each of us.” -Lisa Kleypas

Ah, but what if you did want the scientific view of starlight? After all, it's through the very stars themselves that we've unveiled some of the greatest secrets of the Universe.

Image (mosaic) credit: Nick Risinger.

But while the stars of the night sky may appear mostly white to you (and very similar to one another), the reality is that they come in a wide variety of colors and intrinsic brightnesses, as this famous photo from the Hubble Space Telescope demonstrates.

Image credit: NASA, ESA, and the Hubble SM4 ERO Team.

Believe it or not, every individual star in the Universe has -- barring a merger with another star -- its fate completely determined from birth. Here's how it all work, from beginning to end.

Image credit: Josh Walawender of Twilight Landscapes.

When a large enough molecular cloud -- a cloud of cold, hydrogen-rich gas -- collapses, a significant fraction of the cloud forms new stars. How is that mass distributed? It's spread out (roughly) evenly, by mass, among the seven major different main-sequence star types.

Image credit: Wikipedia user Kieff.

Of course, that means that only about 0.12% of the stars will be O-and-B-type stars by number, while around 75% will be M-stars. Unsurprisingly, the O-stars will be the brightest of all the stars, as, being the most massive, they also burn through their fuel the fastest, which makes them the most luminous. It's the reason why -- when we look at a very young star cluster -- we find it dominated by these incredibly bright, blue stars, even though they're vastly outnumbered by much dimmer, redder ones.

Image credit: Langkawi National Observatory @ ANGKASA.

If we were to graph the luminosity, or intrinsic brightness of each star in the cluster on the y-axis, and the color (bluest to the left, reddest to the right) on the x-axis, we'd get a path that snakes upwards. This type of diagram is known as the Hertzsprung-Russell Diagram (or H-R diagram for short), and the snaking path is known as the main sequence, which is where stars that are primarily burning hydrogen in their core all live. (And yes, this includes our Sun!)

Image credit: Atlas of the Universe / Richard Powell.

But over time, stars run out of hydrogen in their core, and the bluest, most massive stars burn through their hydrogen the fastest! A brand-spankin' new cluster of stars will only have main sequence stars, while an older population of stars will have an H-R diagram that looks much more complicated. For example, globular cluster M55 (maybe next week's Messier Monday?) is quite old, and its H-R diagram looks like this.

Image credit: B.J. Mochejska, J. Kaluzny (CAMK), 1m Swope Telescope.

The high-mass stars -- all the ones more massive than the Sun, in this cluster's case -- have all long since ceased burning hydrogen in their cores. (Those few main sequence, blue stars to the left of the turnoff are known as blue stragglers, and they come from two lower-mass main sequence stars merging.) When this happens, pretty much every star will have its core, now devoid of hydrogen, begin to contract. And thanks to your friend thermodynamics, when the core of a star contracts under these conditions, it heats up. Eventually, it heats up enough that hydrogen will begin fusing in a shell around the core, which causes the star to swell. (Every star type will do this except M-stars, which are too low in mass to begin another stage of fusion.)

This results in your main-sequence star evolving into a subgiant, a star that's slightly brighter and slightly cooler than the main-sequence star it formerly was.

Image credit: Procyon photo by Arun Venkatram, inset by David Darling.

This is what's going on with Procyon, one of the brightest and closest stars in the night sky, at just 11.5 light years away. Over a timespan of tens of millions of years, subgiant stars will continue to expand and cool in their outer layers, while their inert cores continue to heat up, eventually reaching a sufficiently high temperature to begin fusing Helium in its core!

At this stage, the star swells immensely, and becomes a true red giant, a phase of evolution that may last hundreds of millions of years, and the phase where stars achieve their maximum luminosity. These stars cool down as they evolve due to their massive, increasing size; just as adiabatic contraction caused the core to heat up, adiabatic expansion caused the surface temperature to drop, even as the overall energy output increases. As the large, red giant begins continues burning helium in its core -- first into carbon and then into oxygen and heavier elements -- the large luminosity remains roughly constant, but the star evolves to become smaller and bluer. For comparison, here's the Sun alongside Arcturus, an orange giant, and Antares, a red giant.

Image credit: Wikipedia user Sakurambo.

This phase of evolution is known as the horizontal branch, and many stars will even migrate back towards the main sequence!

So the sequence for pretty much all K-class stars (or heavier) goes as follows: main sequence (hydrogen core burning) to subgiant (hydrogen shell burning) to red giant (helium core burning) to horizontal branch star (continued helium burning into heavier elements).

Image credit: James Schombert of http://abyss.uoregon.edu/~js/ast122/lectures/lec16.html.

If the star is massive enough to burn Helium in a shell as the core continues to contract, it again moves towards the red end and becomes even more luminous once again. Although it appears to become a red giant of an even higher temperature, this is another, separate evolutionary phase. The name of the phase depends on the mass of the star, as the chart below indicates.

Image credit: Wikipedia user Rursus.

And this cycle continues: the core contracts until shell burning initiates, and -- if possible -- the core will heat up to allow fusion of heavy core elements into even heavier ones (neon, magnesium, silicon, sulphur, and eventually all the way up to iron-nickel-and-cobalt), while the star continues to switch between bluer-and-redder colors but retains a very high luminosity.

Finally, if the original star is below about eight-to-ten solar masses, fusion will end and the star's core will contract down to a white dwarf, blowing off its outer layers in the process and becoming a planetary nebula, which come in a great variety of gorgeous colors and shapes.

Image credit: Carlos Milovic, Hubble Legacy Archive, and NASA.

The remaining cores -- the white dwarf stars -- are only a few millionths as luminous as the original stars they were borne from, although they are generally hotter in temperature and hence bluer in color than the main sequence stars they started off as. And that's the vast majority of stars that have run out of their fuel so far -- all the K-type, G, F, A, and most of the B-type stars -- they all will end up as white dwarfs in the end.

."]

Image credit: European Southern Observatory [ESO

But the stars that began their life as O-type or bright B-type stars, the ones that started with 10 times the mass of our Sun or more, those wind up with core so massive that the individual atoms in the core cannot withstand gravity, and the entirety of the core collapses, producing a spectacular supernova explosion known as a supernova, resulting in either a black hole or a neutron star at the end of those star's lives!

And that's where the entirety of starlight -- from all the different stars in the Universe -- comes from! Now, if only I can get myself on the fictitious H-R diagram of astronomers... until then, enjoy the awesome knowledge that allows you to understand the life cycle of every star in the Universe!

esiegel Wed, 01/16/2013 - 11:43

Tags

fantastic explanation, thanks !!!

Great post, as usual. As soon as I finish teaching about small solar system objects and exoplanets, it's on to the Sun and stars for my astronomy students. I expect to borrow several of your illustrations.

As per the H-R diagram of astronomers, it seems that there are a lot of folks missing. It also seems that there is not really a distinction among astronomers, cosmologists and astrophysicists (if there really IS a distinction). Just to pick someone at random whom I enjoy reading, Lee Smolin has sufficient publications and Google hits to make the chart but is absent.

Oh well, so it goes.

Aristotle had access to the brightest minds of his day. He rejected them because of his false premises.

The Herzsprung-Russel diagram is other way around as usually seen, but that's actually nice. Same thing, nice to see it presented in another way.

Aristotle was a great thinker, but he was only a thinker. The glory of modern science is because it is comprised of thinkers and do-ers. They think, and then they do something to test what they thought about, and they think about what happened, then they do something else.

If Aristotle had been wise enough to actually test his ideas, we might have had Aristotle's Laws of Motion over a thousand years before Newton came along.

I've often thought that there must be a very natural diagram to be plotted, based on the H-R one. Instead of colour and luminosity, use mass and age as the axes, and map out the types of star.

What about those stars that are so massive that, when they go supernova, they leave no remnants behind? I'm sure I've recently read about such stars recently.

You're talking about pair-instability supernovae (http://en.wikipedia.org/wiki/Pair-instability_supernova)

Messier Monday: A Straggling Globular Cluster, M30

esiegel — Mon, 26 Nov 2012 17:17:21 +0000

Messier Monday: A Straggling Globular Cluster, M30

"The man's a born straggler... another lucky exception to the rules of natural selection. A million years ago he would've been an easy snack for a saber-toothed tiger." -Carl Hiaasen

Welcome to the latest Messier Monday, where each week we take a look at one of Charles Messier's original catalogue of 110 deep-sky objects that comet-hunters might easily confuse with those transient passers-by in our Solar System.

Image credit: Greg Scheckler, from his 2008 Messier marathon, where he nabbed 105/110.

Quite to the contrary, each of the 110 objects in the Messier catalogue are (semi-)permanent fixtures in our night sky, and all lie well beyond our Solar System's reach. This week, I'd like to take a look at Messier 30, a globular cluster in the Southern Hemisphere that's still visible just after sunset for those of you (like me) in the north. Here's how to get there.

Image credit: Me, using the free software Stellarium, available at http://stellarium.org/.

Depending upon your latitude, the prominent star Fomalhaut -- the 18th brightest in the entire sky -- will be visible above the horizon in the southern part of the sky just after sunset. For those of you down by the tropics or in the southern hemisphere, Fomalhaut will be easy to spot, but for those of you at high northern latitudes like me (I'm at ~46 degrees north), you'll have to look low for a chance to spot it.

But if you can, look higher in the sky and farther to the west; you'll find a collection of naked-eye stars in the constellation Capricorn.

Image credit: Me, using the free software Stellarium, available at http://stellarium.org/.

Just a little bit back towards Fomalhaut, below the "line" of bright stars in Capricorn, you'll find a really ancient globular cluster, Messier 30, whose oldest stars are 12.93 billion years old, or 94% the age of the Universe!

Through a small telescope or large binoculars, it's clearly a compact, star-filled object.

Image credit: Fred Espenak of http://astropixels.com/.

But you don't really get a sense of scale for this object unless you take a closer, more powerful look. Either a modest (6") telescope with an excellent camera,

Image credit: Sergio Eguivar of http://cs.astronomy.com/asy/m/starclusters/488320.aspx.

or a large (12.5") telescope with just a simple camera,

Image credit: user clasley of Astrobin: http://www.astrobin.com/14160/.

reveals the truth: that this is a cluster with a very dense core, and a population of uncharacteristically bright, luminous, blue stars. At nearly 30,000 light-years distant with a mass of about 160,000 suns, Messier 30 is only about 93 light years in diameter, but has a very dense core and, like I said, bright blue stars sprinkled throughout it, but bluer at the core.

Image credit: NASA / ESA, Hubble Space Telescope.

Which, as you may know, should not be the case for an object that's practically 13 billion years old!

Why not? Here's the thing: stars come in a wide variety of colors, magnitudes and sizes. When a star cluster -- whether an open cluster within our galaxy or a globular cluster like M30 here -- is created, it produces seven different classes of stars, ranging from the brightest, bluest, hottest and most massive type (O-stars) to the dimmest, reddest, coolest and least massive types (M-stars).

Image credit: wikimedia commons user Rursus.

The brightest stars burn through their fuel the fastest, and therefore live the shortest. By time even one billion years goes by, there are no O-or-B stars left; by time 13 billion years have passed, only K-and-M stars will remain.

The remaining stars, when they run out of hydrogen in their core, undergo a variety of well-understood processes, and when we measure the color and magnitudes of the stars in a cluster, the shape that a complete graph of all such stars in the cluster makes gives us an idea of how old that cluster is.

Image credit: wikipedia user Worldtraveller.

By measuring this "turn-off" temperature, we can determine the age of any star cluster. And that's how we know the age of this particular one, Messier 30. Only, that doesn't explain the blue stars in there.

In fact, these blue stars appear to mess up the Hertzsprung-Russell diagram, because they exist in a place where -- according to the standard picture I just painted for you -- they ought to not exist! And yet, there they are.

Image credit: Dr. Helmut Jerjen for Mt. Stromlo Observatory at ANU.

So what's going on here? Quite clearly, there are bright, blue stars -- these so-called Blue Stragglers -- that exist in these clusters. A close-up look at the Hubble image from above reveals this without a doubt.

Image credit: NASA / ESA, Hubble Space Telescope.

And when I told you it was an even more severe effect in the core, I wasn't lying to you; a visual inspection allows you to verify this for yourself! (At least, it's clearly less yellow, even if you can't easily tell it's more blue.)

Image credit: NASA / ESA, Hubble Space Telescope.

What's gone on over here? While a burst of star-formation could have, in theory, been responsible, this is one of the densest globular clusters in the core region ever discovered, with a central density of over 30,000 solar masses per cubic light year! This means the cluster has undergone core collapse, a gravitational process where the center of such a cluster becomes incredibly dense and just keeps increasing the closer you get to the center.

And when this happens, there are two processes that can turn these old, low-mass, doddering stars into bright, short-lived blue ones!

Image credit: NASA/ESA.

Either, as shown at the top, two low-mass stars can merge, creating a heavier, bluer, hotter star that will burn through its fuel faster. This explanation makes a lot of sense, particularly when the stellar density is very high! Or, as shown at the bottom, a star in a binary system can steal mass from its companion, changing its color and luminosity in the process.

There is some evidence that the collision idea is dominant, but that both processes take place. And that's why, after nearly 13 billion years, Messier 30, one of the oldest globular clusters in the entire Universe, contains more than its share of young-looking, hot blue stars: blue stragglers! So take a look inside; you won't regret it!

So, including today’s entry, we’ve covered six of the 110 Messier objects so far:

M1, The Crab Nebula: October 22, 2012
M8, The Lagoon Nebula: November 5, 2012
M15, An Ancient Globular Cluster: November 12, 2012
M30, A Straggling Globular Cluster: November 26, 2012
M45, The Pleiades: October 29, 2012
M81, Bode’s Galaxy: November 19, 2012

Which one will be next? Join me next Monday for our seventh entry, and let me know what you'd like to see next! There'll be a new Messier object — and a new window into the night sky — waiting for you to discover!

esiegel Mon, 11/26/2012 - 12:17

Tags

Globular clusters, no matter how we try to pigeon hole them, are going to surprise us. Why they even exist is reason enough. Plus ... being in one !!! A thousand sunsets everyday!

The only way to start the week. Messier Monday!

I <3 globs.

Interesting to see that there's now evidence for the existence of and even the frequency of the two paths to forming blue stragglers. It seems only recently that it was a true mystery with those paths only proposed explanations. The article is dated 2009; only 3 years from publication to entering my consciousness isn't so bad as such things go. :)

Now here is a question. And I preface it with the remark that I really don't know what I am talking about and may be badly mixing up unrelated ideas.

So I defer to whoever understands better.

Why not? Based on:
-this post and
-Ethan recent post http://scienceblogs.com/startswithabang/2012/11/07/every-galaxy-will-ha…

And the discussion in that recent posted end pretty much with a problem between Ethan's hunch and David's measurements.

Ethan's hunch, ", “My hunch is that, as the SFR density drop below a certain threshold, the slope will change, either becoming constant or dropping at a much slower rate, drastically altering (upwards) the total number of stars as we allow t –> infinity. It may take much longer than trillions of years, but it’s hard to envision a self-sustaining star-suppression scenario that last an infinite amount of time without expelling the gas. (And violent relaxation won’t do it.)”

Ethan in that post explained, "Here’s the thing: if you add up all the normal matter in our galaxy — all the protons, neutrons, and electrons — most of it is still neutral hydrogen gas! We’re in no danger of running out anytime soon."

And Wow said, " the premise upon which the claim “95% of the stars in the universe that will ever exist have already been born” is based on faulty reasoning and curve-fitting."

And David Sobral said, "The Universe is certainly not done forming stars, but it is doing it at a rate which is much lower and which has been declining continuously over the last 11 billion years."

David Sobral also suggested, "please make up your sophisticated theoretical model to give me an actual prediction. Things it need to reproduce for me to believe it:
- Evolution of the star-formation rate density
- Evolution of the stellar mass density
If it complies to both and get a completely different result then you should publish it right away in Nature and you’ll solve all problems to do with galaxy formation and evolution."

Ahha! Now here is the thing.

Ethan has a hunch that star formation will continue. Reasonable.
David has measurements that show a 11 Bill years of decline. Reasonable/.

But!! We don't have a good enough theory of evolution of star formations, evolution of galaxies, and evolution of globular cluster; and that relates these three evolutions together in some uber galactic cycle of star formation.

Now what could be consistent with both Ethan's hunch and David's measurements? The measured decline in star has to stop. When? How?

Well maybe it has stopped in the last 1 billion years and with careful measurements we can see it. But if it doesn't stop for another 10 billion years, then we've just got another hunch.

Unless we can see something now, like globular cluster M30's surporising formation of new stars.

Now M30 is as old as globular clusters get at 12.93 billion years old. But it's star formation is current history; it is a mere 30,000 lightyears from Earth. M30 is a globular cluster that is orbiting the MilkyWay!

So here we have a surprise turnaround in star formation. We have a new mechanism. Old sttars, maybe brown dwarfs and white dwarfs that have until now (i.e. over the 11Billion years of David Sobral's research) have not interacted in a way that releases the unspent hydrogen in brown dwarf stars.

But if in globular clusters like M30, those old "dead stars" combine, new stars are born.

So maybe what we need is a comparision of the star formation in old globular clusters over time from 11 billion years ago to now. Yes yes, I know we don't have the james Webb or a super James Webb yet. But I predict that the nearer the old globular cluster; the faster the star formation rate.

Thus a possible mechanism for Ethan's hunch. And a observational measurement challenge for David. Maybe the data is already partially available. I mean ther has to be at least a dozen old M30 like globular clusters already observed some near, some far.

I've said enough. Now I will listen and see if someone who understands better than I tells me that what I say is:
1)possible but we'd need a lot more data and better models of star, glob cluste and galaxy formation and interaction, etc..
2)doesn't solve the problem of David's measurements versus Ethan's hunch because.. of this and that
3) here's a better thought.

So, someone please comment and educate me. thanks.

And David Sobral said, “The Universe is certainly not done forming stars, but it is doing it at a rate which is much lower and which has been declining continuously over the last 11 billion years.”

Which is curve fitting.

Counting the number of hurricanes hitting New York City you have seen a massive reduction recently.

Ergo, there are less than 3% of the number of hurricanes that will ever hit NY left to go.

Wow
I'm not interested in repeating the arguments of the referenced post.

I am asking a new question about this post.

So if you have a reflective thought about my question about M30 type globular cluster; then I'd like to hear it.

I'm interested in your THOUGHTS; not in your ranting..

So, any thoughts ON THE TOPIC of my question about M30 type globular clusters?

Well if your wall-o-text pertained to this:

"Ethan has a hunch that star formation will continue. Reasonable.
David has measurements that show a 11 Bill years of decline. Reasonable/.

But!! We don’t have a good enough theory of evolution of star formations, evolution of galaxies, and evolution of globular cluster"

The problem is that David has something about the past that only talks about the past and then pushes that past into the future for no reason.

You know, curve fitting.

I really don't know how clearer to put it, but you're there saying "So it's red. But what is the colour of it?" repeatedly.

David has done no different than looking at the past 8 months of hurricanes in NY state and then claimed that there is such a huge drop off that if this continued, there are likely only a few hurricanes left.

Despite the elements that allow hurricanes to form and arrive in NY remaining.

How?

By curve fitting and ignoring the method by which the events occur, because the curve doesn't tell you anything about that, merely the count over time.

David's message has nowt to do with M30.

OKThen, a perhaps niggling but important point on nomenclature and classification:

It's not "brown dwarf star", it's just "brown dwarf". Brown dwarfs are by definition sub-stellar objects that never underwent sustained fusion of hydrogen. They did fuse some deuterium, but the rate of such fusion would have dropped off steadily. As would the temperature of the object, very similar to how gas giants and other planets have a steadily decreasing temperature as the heat from their formation is released. Unlike stars which maintain a minimum luminosity over their lifespan due to sustained hydrogen fusion -- and the ones just enough big enough than brown dwarfs to do it, do it the longest, making for a stark contrast.

It's a little confusing, because "red dwarfs" are actually stars, just really small and dim ones, but like I mentioned long-lived.

And "white dwarfs" are the remnants of stars too small to become neutron stars when they die and their cores collapse into a super-dense (but not ridiculous-dense or ludicrouse-dense like neutron stars and black holes) ball of electron-degenerate matter with no fusion occuring.

Black dwarfs are what white dwarfs will become after they finish cooling off, which won't be until the universe is something like 10,000 times older than it already is.

Wow
You are quite determined to beat a dead horse.
I'm happy to leave the discussion of the previous post and comments, which speak for themselves.

So stop and read my question (or NOT) about the surprising star formation (by whatever mechanism) in this 12.9 billion year old but very near globular cluster M30.

If you have any thoughts about the importance of M30 star formation process vis-a-vis my question; well then share your thoughts. That's all.

"The Sonic hedgehog (Shh) signaling (protein) molecule (which) assumes various roles in patterning the central nervous system (CNS) during vertebrate development" is not an issue in this discussion either.

If professional astronomers are too timid to address my question; then I stick by this explanation.

"Stars in globular clusters are generally believed to have all formed at the same time, early in the Galaxy's history 'Blue stragglers' are stars massive enough that they should have evolved into white dwarfs long ago." arXiv:1001.1096

"Globular clusters, which are found in the halo of a galaxy, contain considerably more stars and are much older than the less dense galactic, or open clusters, which are found in the disk." wikipedia

"Surprisingly, we ﬁnd that the simple correlation with core mass remains by far the strongest predictor of blue straggler population size, even in our joint models. This is despite the fact that the binary fractions themselves strongly anti-correlate with core mass, just as expected in the binary evolution model." arXiv:1210.0542

So the problem is that halo globular clusters should have the oldest stars; but M30 and other old globular clusters are forming new stars blue stragglers and the "core mass remains.. the strongest predictor of blue straggler population size... (and).. binary (stars).. strongly anti-correlate".

Let's believe this data is good rather than bad as the researchers assume. "most appealing, is that observational uncertainties aﬀecting the core binary fractions exceed the intrinsic scatter of the relationship between binary fractions and core mass. This could reconcile the data with the binary evolution model."

But why do they assume the data is bad? Answer, to keep and support the present model, i.e. "reconcile the data with the binary evolution model." Not very bold. In fact, it is stupid to assume that the data is incorrect to save a model.

So what we have is globular clusters migrating from near the galaxy disk to further out near the halo. And as the globular clusters get further out; there stars are older and older (i.e. 11 to 13 billion years old stars). Yes, even though they are in the local vicinity of the local galaxy (e.g. the Milky Way).

But the paradox is that the oldest globular glusters like M30 start forming new stars. " 'Blue stragglers' are stars massive enough that they should have evolved into white dwarfs long ago."

But we don't see white dwarfs; instead we see new star life, i.e. blue stragglers.

Hence instead of locking hydorgen forever in white dwarfs as suggersted by Sobral; we see a possible mechanism for unlocking that hydrogen as hunched by Ethan.

But Ethan remains silent, and Wow becomes indignant. But both refuse to answere my question. Why??

Because research into ancient globular clusters not only offers a mechanism for new star growth (i.e. blue stragglers due to collision Not binary) i.e. " 'Blue stragglers' are stars massive enough that they should have evolved into white dwarfs long ago." But also, ancient globular clusters offer a problem to the standard model of cosmology. So hush, hush, let's not answer that question.

"these 9 GCs (globular clusters) have not been used to study the cosmic age problem in the previous literature...
Globular Cluster... Age(Gyr)
-----B024 ...........15.25 ± 0.75
-----B050........... 16.00 ± 0.30
-----B129........... 15.10 ± 0.70
-----B144D........ 14.36 ± 0.95
-----B239............ 14.50 ± 2.05
-----B260.............14.30 ± 0.50
-----B297D......... 15.18 ± 0.85
-----B383............ 13.99 ± 1.05
Therefore, if the age estimates of these objects are correct, the cosmic age puzzle still remains in the standard cosmology. Moreover, we extend our investigations to the cases of the interacting dark energy models... the interacting DE models still have diﬃculty to pass the cosmic age test... Therefore, the cosmic age problem still needs to be further investigated in the future work." arXiv:1005.4345

So if you say nothing and pretend that globular clusters and blue stragglers have nothing to do with the issue of new star formation in the distant future (i.e. Every Galaxy will have New Stars for Trillions of Years!); then you will not have to deal with the bigger problem that there are nine old globular clusters that are older that the 13.7 Gyr of the universe.

As an amateur, I am an intellectual without allegiance to any authority (e.g. standard model, religion, philosophy, etc.). I do recognize my limitations in understanding the technical talk of astrophysicsits and would much prefer the explanation of an astronomer.

But, if professional astronomers are too timid to address my question; then I stick by this explanation.

Every Galaxy will have New Stars for Trillions of Years!

esiegel — Wed, 07 Nov 2012 17:07:53 +0000

Every Galaxy will have New Stars for Trillions of Years!

"It's a brilliant surface in that sunlight." - Neil Armstrong

Indeed, all that glitters so brilliantly in the cosmos does so because of the stars that have formed throughout it.

Image credit: NASA, ESA, and the Hubble SM4 ERO Team.

Over the 14 billion-or-so years that our Universe has been around, we've formed hundreds of billions of stars in our galaxy alone.

Image credit: ESO / Serge Brunier (TWAN), Frederic Tapissier.

Given that our galaxy is just one of at least hundreds of billions in the observable Universe, the number of stars that have formed over our Universe's history is a tremendous number, when you add them all up.

Image credit: NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team.

But one of the fun things we discover is -- by looking back at the younger galaxies in the Universe -- the star formation rate back then was much higher than it is now! A typical galaxy from long ago is forming more stars on average than a galaxy now.

Image credit & copyright: Tony Hallas.

This galaxy -- the Sunflower Galaxy -- is typical of galaxies today. You can identify star-forming regions in galaxies from the characteristic pink glow that star-forming regions give off, thanks to their ionized hydrogen.

Do you see how, above, there are only a few, small pink regions in that galaxy? This is a classic example of a mature spiral galaxy, where it's full of gas, dust, and stars, all clearly visible in the snapshot here, but only a few sparse regions are currently forming stars.

This was not always the case for this galaxy, and it won't always be the case for this galaxy going forward into the future, either. Why not?

Image credit: NASA, ESA, S. Beckwith, and The Hubble Heritage Team (STScI/AURA).

Because events are going to happen that cause this gas and dust to contract and form stars. It can happen in large bursts, like due to a gravitational interaction (above), it can happen gradually over time, triggered by something like a nearby star's explosion, or it can happen in the most spectacular way imaginable: in a huge rush caused by a major merger with a comparably-sized galaxy.

In this last case, the entire galaxy will become a star-forming region, and this is known as a starburst galaxy.

Image credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA).

Incidentally, this will be us in about 4 billion years, when the Milky Way and Andromeda undergo a major merger. Our night sky will look something akin to this, as our entire system of merging galaxies will be forming new stars.

Image credit: NASA, ESA, Z. Levay and R. van der Marel (STScI), and A. Mellinger.

But -- you may be curious -- how long can this process go on for? Sure, we'll form stars in great, periodic bursts when rare, catastrophic events occur, and very slowly and intermittently otherwise. But at some point, we're going to run out of the hydrogen gas that -- at one point -- comprised 92% of the atoms in the Universe. Because stars work by fusing light elements into heavier ones, at some point in the future, we'll have fused all the elements we're going to form.

Well, here's what you definitely shouldn't do.

Screenshot of: http://www.wired.co.uk/news/archive/2012-11/07/star-production-down-97-….

You shouldn't, David Sobral, make statements like this (bold emphasis mine):

You might say that the universe has been suffering from a long, serious "crisis": cosmic GDP output is now only 3% of what it used to be at the peak in star production! If the measured decline continues, then no more than 5% more stars will form over the remaining history of the cosmos, even if we wait forever.

Image credit: Charles M. Schulz.

Let me tell you something about our galaxy. Our unexceptional, unremarkable, uninteresting-save-that-it-contains-us galaxy. This guy, shown vertically so you can get a good look at it.

Image credit: Alan Dyer.

Sure, with your eyes, you're going to notice mostly the stars, and -- in pink -- the small and sparse star-forming regions. But you may also notice the dust lanes!

Here's the thing: if you add up all the normal matter in our galaxy -- all the protons, neutrons, and electrons -- most of it is still neutral hydrogen gas! We're in no danger of running out anytime soon.

However, we went through intense periods of star formation in the distant past. We observe these -- in and around our galaxy -- all across the Universe as still being an ongoing thing.

Image credit: NASA, ESA, R. O'Connell, F. Paresceysics, E. Young, the WFC3 Science Oversight Committee, and the Hubble Heritage Team (STScI/AURA).

When this happens, only about 10% of the gas that made up these star-forming regions actually gets locked up in stars, with the remaining 90% evaporating and getting blown back into the interstellar medium, where it will someday form stars again in the future.

Furthermore, most of the stars (in terms of mass) that form will eventually die in either a supernova or a planetary nebula, returning a huge fraction (perhaps half of a star's worth) of unburned fuel back to the interstellar medium on top of the large gas fraction that never formed stars during the initial starburst!

Image credit: Kunihiko Okano's Gallery; http://www.asahi-net.or.jp/~RT6K-OKN/.

Since it's in a gravitationally bound system -- a galaxy -- it's only a matter of time and gravity, neither of which are going anywhere, before all of the gas eventually forms stars.

The thing is, it's going to take a looooong time -- many trillions of years, by my estimates -- until we're out of fuel. Why's that? Because, when Sobral says "If the measured decline continues," that's his big flaw. Yes, there's an initial burst of star formation that's huge, and occasional bursts like that will punctuate the timeline of the Universe and dominate the measured star formation rate. But there's a slow, steady component on top of that, and as long as gas is abundantly present within our galaxy, that measured decline will not continue arbitrarily far into the future.

And the thing is, Sobral's a good enough astronomer that he knows it.

You KNOW better, man. You. Know. Better.

Yes, it's interesting that the star formation rate has declined, and it's interesting that it's declined at the rate we've observed. But it's not going to drop to zero any time soon, and if you sum up the total number of stars in our Universe's future, it's actually far greater than the number of stars that have already existed up until this point in time, a far cry from the "only 5% more than we have now" figure you may have read.

Although we might be approaching the peak of star density within our galaxy, we can very strongly say that the vast majority of stars that will ever call our galaxy home haven't been born yet.

Image credit: Don Figer (STScI) et al., NASA, of the Quintuplet Star Cluster.

We won't live long enough to see them, either, as many trillions of years into the future is far too ambitious to count on, even for those of you counting on the singularity. But based on the physics and astronomy we know, there will be new stars for ages and ages to come, outnumbering even the full complement of stars that have ever existed up until today.

esiegel Wed, 11/07/2012 - 12:07

Tags

What a wonderful blog entry! Fascinating!

Reminder of our insignificance, yet gives great reassurance that even when life as we know it ends in our neck of the universe, there is tremendous opportunity for it to arise over and over and over again. Nice post as usual and that vertical pic of the milky way is impressive to say the least. what a beautiful image.

Awesome! What about the Big Rip? I mean, at scales of trillions of years won't cosmological evolution impact processes such as star formation? Also, will long-lived stars, namely M-dwarfs, come to dominate?

And what about black holes? Won't they tend to increase in number and mass over billions and trillions of years? Any possibility that this might compound to become significant enough to affect your projections?

Our ripping apart the LMC is the cause of massive increases in the production of stars both in that dwarf galaxy and ours.

"Every Galaxy will have New Stars for Trillions of Years!"

All scientific predictions are
1) about the future
2) based on scientific theories
3) falsifiable

In general a prediction is a statement about the future, based on scientific theories to which we really don't know the answer. We have an answer based on the theory; but if it has never been tested and determined by experiment or observation; thus there is the possibility of new science being discovered if the prediction is shown to be incorrect.

The statement "Every Galaxy will have New Stars for Trillions of Years!" is not a scientific prediction; because it is not falsifiable. Such a statement can neither be used to prove or to disprove current cosmological theories; because it is not falsifiable.

"Cloned woolly mammoth will be brought back to life in the next 10 years." is a scientific prediction because it is:
1) about the future
2) based on scientific theories
3) falsifiable
http://news.yahoo.com/blogs/technology-blog/scientists-bring-extinct-wo…

"Every Galaxy will have New Stars for Trillions of Years!" is a metaphysical statement; since it is not falsifiable (at least not for a trillion years).

Well, you could be pedantic and say that all science theories are predicting the past... The theories change when the future becomes the past and the prediction doesn't materialise.

The statement “Every Galaxy will have New Stars for Trillions of Years!” is falsifiable just like any prediction. Wait to see if it turns up or not.

But the premise upon which the claim "95% of the stars in the universe that will ever exist have already been born" is based on faulty reasoning and curve-fitting.

I.e. non scientific guessing.

And the prediction, like the obverse, could be proven or disproven merely by waiting a trillion years.

But the basis of the predictions for one exists in reality. The other doesn't.

Great blog entry and I quite liked the point that you made about *our galaxy*. But the study has nothing to do with our galaxy. It has to do with the Universe as a whole, statistically. As as a whole, the star formation rate density (which is the amount of mass of new stars produced in a given average volume) is really low compared to the past, so *on average* the total stellar mass density will not really grow that much (because there are soooo many stars already compared to the rate of formation of new ones).

Obviously, this is a statistical observation - but you know very well that saying "humans are getting on average more obese in developed countries" *does not* mean that a particular person/(galaxy) is getting obsess. Let me know if this makes it clearer - the conclusion is for the Universe as a whole, and for an average volume of the Universe, not for a single galaxy, not for our galaxy

David,

If what you are talking about is "star formation rate density," the number of stars formed per-unit-time-per-unit-volume, I would be greatly confused. That seems like an extremely uninteresting thing to measure, as the expansion of the Universe will dominate everything unless you use comoving volume.

If you do use comoving volume, and scale out the expansion of the Universe -- for instance, considering the galaxies within a comoving volume -- then I would imagine your conclusions change dramatically. Yes, most of the stars are old, but the once the stars that we have now burn out, that's hardly the end of "stars" in any galaxy in the Universe.

The articles that have been written up about your research give the strong impression that we are almost done forming all the stars in all the galaxies in the Universe, a conclusion that is certainly not true. I did not mean to be critical of your research, but rather how it was picked up and interpreted by the press, as it created a faulty impression about the Universe that I sought to correct.

"the conclusion is for the Universe as a whole, and for an average volume of the Universe"

Here's the problem in a nutshell.

The volume of the universe is getting bigger AND stuff is falling off the edge of it.

You also have the problem of backcataloguing: those distant galaxies are much, much, MUCH younger.

And, moreover, were formed in the past. 10 billion years ago, those stars didn't have a universe 10 billion years old to look at.

Obviously what we measure, and refer to as star formation rate density (which is a fundamental measurement of galaxy formation and evolution), is using co-moving volume (otherwise, as you say, it would be meaningless and simply dominated by the expansion of the Universe).

The Universe is certainly not done forming stars, but it is doing it at a rate which is much lower and which has been declining continuously over the last 11 billion years. The decline measured by us allows to predict the total mass of stars per co-moving volume and compare to actual measurements of stars per co-moving volumes (from e.g. infrared light and info from the full SED): it's a really great match. So our measured decline as a function of time is able to fully reproduce the evolution of the stellar mass density (co-moving, again, of course). This encouraging "prediction"-power is what is used to extrapolate to the future: if the star formation rate density continues to decline it is very very simple: the fraction of mass formed in new stars formed at time t divided by mass of existing stars becomes smaller and smaller and smaller.

But, of course, the complete shut-down would only happen at t=infinity. There will be trillions and trillions of new stars being formed from now to the future: but the point is that relative to those that exist (in mass) they will only represent a 5% increase in this scenario (averaged over the Universe, not necessarily valid for any single galaxy).

"star formation rate density (which is a fundamental measurement of galaxy formation and evolution)"

No, collapse of hydrogen gas clouds are a fundamental measurement of star creation.

Where there is no gas, there is no chance of gas collapse.

Where there is no perturbation of the gas, there is little chance of gas collapse.

There are lots of stars being born at the leading edge of a spiral arm of a galaxy. Naff all at the arse end of it.

The density therefore is nothing to do with the rate of star creation, and you haven't even addressed what the heck you mean by "galaxy evolution".

Unless you think that globular galaxies are older spiral galacies and the latter morphs into the former, which AFAIK is still about as well supported as Brane Theory, what on earth is galactic evolution?

Hence I've ascribed it to the only thing that makes sense: the formation of the stars within that galaxy.

David,

So, where I said:

Because, when Sobral says “If the measured decline continues,” that’s his big flaw. Yes, there’s an initial burst of star formation that’s huge, and occasional bursts like that will punctuate the timeline of the Universe and dominate the measured star formation rate. But there’s a slow, steady component on top of that, and as long as gas is abundantly present within our galaxy, that measured decline will not continue arbitrarily far into the future.

And the thing is, Sobral’s a good enough astronomer that he knows it.

Are you suggesting that the star-formation-rate-density is going to continue to decline at the steep rate it's declined at arbitrarily far into the future? No slowing or asymptoting of the decline?

In short, stars form for a reason.

And that reason is mechanistic, not statistical. It doesn't give a stuff for "star formation rate density".

The latter is measured from the former, the former doesn't follow from the latter.

Cause THEN effect.

"...many trillions of years into the future is far too ambitious to count on..."

I just wanna watch the collision with Andromeda, will that be OK?

Ethan,

We can only hope to know/quantify what we can actually measure. This is what is measured: over the last 11 billion years there has been a continuous decline - that's one of the simple results coming out of the paper. No slowing down in the decline, just a continuous decline - which is actually quite simple: log(SFRD)=-2.1/(1+z) where z is redshift and SFRD is the star formation rate density.

I realize now that most people here are thinking about the star formation history of our galaxy, or particular galaxies. That's not what this is about: it's about the Universe as a whole - the whole population of galaxies at a given time. And this is only possible because the volumes we targeted are really large and spread across independent regions in the Universe. These are volumes of about 1000000 Mpc^3 co-moving (even though we are looking at "slices" in time, these "slices" do have a little nice depth).

Wow: have a look at a few textbooks, articles and talk with friendly astronomers/cosmologists: they will explain why statistical studies of the Universe are absolutely fundamental. That doesn't mean that individual cases and very detailed physical studies of individual gas clouds/star-forming regions are not absolutely fundamental to unveil the physics behind star-formation - of course they are, because without them any other study becomes meaningless.

Let me put in my 2 cents (as layman, not a professional astronomer)

Looking at David Sobral's paper
THE PROPERTIES OF THE STAR-FORMING INTERSTELLAR MEDIUM AT z = 0.8–2.2 FROM HIZELS: STAR-FORMATION AND CLUMP SCALING LAWS IN GAS RICH, TURBULENT DISKS, 2012, by A. M. Swinbank, Ian Smail, D. Sobral, T. Theuns, P. N. Best, J. E. Geach http://arxiv.org/pdf/1209.1396v1.pdf

Sobral et al's work appears to be an excellent piece of work.

"The majority of the stars in the most massive galaxies (M⋆ >
∼ 10^11 M⊙) formed around 8 –10 billion years ago, an epoch when star formation was at its peak. Galaxies at this epoch appear to be gasrich (fgas = 20 – 80%)... In order to reﬁne or refute these models, the observational challenge is now to quantitatively measure the internal properties of high-redshift galaxies, such as their cold molecular gas mass and surface density, disk scaling relations, chemical make up, and distribution and intensity of star formation."

See right here Sobral et al are making a scientific prediction with the words, " In order to reﬁne or refute these models, the observational challenge is now to quantitatively measure"

Whereas Ethan makes a metaphysical statement, "Every Galaxy will have New Stars for Trillions of Years!" Sorry Ethan and Wow, but this is metaphysics not a scientific prediction. And now I am not being pedantic; because falsifiabelity (i.e an observation that will "reﬁne or refute (a) models" in the sense that Sobral et al's work is at the heart of a scientific prediction!!!.

Sobral et all dare to make a real scientific prediction. They point to exactly what observations are needed to "reﬁne or refute these models". They say, "the observational challenge is now to quantitatively measure the internal properties of high-redshift galaxies, such as their cold molecular gas mass and surface density, disk scaling relations, chemical make up, and distribution and intensity of star formation. " Very Nice. Excellent actually!!

Sobral et all go on to say why these measurements are important. "Indeed, constraining the evolution of the star formation and gas scaling relations with redshift, stellar mass and/or gas fraction are required in order to understand star formation throughout the Universe. In particular, such observations are vital to determine if the prescriptions for star formation which have been developed at z = 0 can be applied to
the rapidly evolving ISM of gas-rich, high-redshift galaxies)"

Part of Sobral et al's conclusion is "Overall, the scaling relations we have derived suggest
that the star formation processes in high-redshift disks
are similar to those in local spiral galaxies, but occurring
in systems with a gas rich and turbulent ISM. Given the
paucity of gas-rich, clumpy disk-like high-redshift galaxies, the next step in these studies is to spatially resolve the cold molecular gas via CO spectroscopy in a well
selected sample in order to better constrain the interation between star-formation and gas dynamics. Through comparisons with cosmologically based numerical simulations,
such observations may begin to diﬀerentiate whether the
dominant mode of accretion is via three-dimensional cold
gas ﬂows accrete from the inter-galactic medium, or from
two-dimensions from outskirts of the disk as gas cools
from the hot halo."

I do not pretend to understand Sobral et al's work in the detail or in the larger context of astronomy cosmology research. But it seems mighty unsicientific of Ethan to censure Sobral et al based on what they say in the popular press rather than what they say in their published paper.

Ethan says, " “If the measured decline continues,” that’s his big flaw... And the thing is, Sobral’s a good enough astronomer that he knows it." Ethan can you honestly say that you looked at Sobral's published research before you made this statement. "That's a big flaw if Ethan didn't, and he's a good enough scientist that he knows it."

And I might add that Ethan's censor of Sobral et al better applies to his own imprecise popular science predictions, "If you sum up the total number of stars (or planets, or galaxies, or black holes, or microorganisms, or spatial dimensions, or inhabited planets, or poets, or books, or computers, or anything) in our Universe’s future, it’s actually far greater than the number of stars (or planets, or galaxies, or black holes, or microorganisms, or spatial dimensions, or inhabited planets, or poets, or books, or computers, or anything) that have already existed up until this point in time".

So what exactly is the point of Ethan's metaphysics. Certainly not to "reﬁne or refute some scientific model or theory."

Excellent scienbtific research and predictions Sobral et al

"Whereas Ethan makes a metaphysical statement, “Every Galaxy will have New Stars for Trillions of Years!”"

Nope, it is exactly the same science as the earlier statement.

Sobrel is reifying (or the media in describing it is doing so and Sobrel is not clarifying) the observation of an epoch of high stellar formation at a time ago and making that something real.

Look at the moon.

Look at the craters.

Around the same time, the solar system was bombarded with debris and formed craters all over the system.

Masses of the bastards.

But does that mean we aren't seeing any craters being formed today?

No comets?

No.

The oort cloud is the source of comets and the asteroid belt another.

Still plenty where that came from.

And so comets will continue to fall in for billions of years in our solar system.

Sobrel may be making a scientific prediction in your opinion, but it's no more scientific a prediction than mystic meg. Just because you can see whether she's making accurate predictions doesn't make her astrology predictions scientific.

"I just wanna watch the collision with Andromeda, will that be OK?"

Well the first million years waiting were the worst. Then the next million years? Even worse. After that it just went downhill.

To call a part of the cosmological narrative of the standard model metaphysics is not to disparage it.

All histories of the universe as told from the prehistoric to biblical to modern times to our great great grandchildren times are in part fanciful stories that tell more about the storyteller than about the universe.

Story tellers start out with the reasonable, the earth, the sun, the moon the seasons etc; things in the universe that have been or can be observed by any human.

But then all stories of the universe, make necessary metaphysical assumptions. These are the things that can never be observed but that seem reasonable and necessary to tell a coherent story of the universe. And scientific story tellers are no different, scientists make reasoned metaphysical assumptions.

Thus even though, all of the theories of science do not fit together perfectly (i.e. there are gaps in our knowledge, there is conflicting evidence, there are multiple reasonable interpretations); scientists (like other storytellers) often tell a big picture, big history, big bang story of out universe that goes from before the big bang (and may even include multiverse, bublble and other universes) right up to the present and beyond to the future (sometimes to as far "Collapse of iron star to black hole
10^10^26 to 10^10^76 years from now". And the variety of these big universe stories are many (as there are scientist telling); because each one makes a little different metaphysical assumption.

For the fate of the universe we have open universes, closed universes, big crunches, big bounces, big freezes, cyclical universes, multiverses, extra-dimensions etc. In my mind these fates of the universe are all part of the metaphysics of cosmology. they are part of the ultimate narrative of particular thoeries (based on the same scientific evidence) but interpreted differently by some different underlying assumption (i.e. metaphysical assumption, unprovable at least yet).

Now for me personally, I draw the line between metaphysics and physics between events that are in the observable and events that are not observable in the time range observed by scientists EVER.

The smallest time interval ever observed is about 10^-25 seconds. (various measured quark/gluon or electron/photon emissions)
The largest time interval ever observed (i.e. oldest object) is about 10^18 seconds (approximately the age of the universe)

Thus, for me, events outside of this observed time range (10^-25 sec to 10^18 seconds) are metaphysical.

Yes. the Planck time 10^-43 seconds, is a useful number for trying to build a GUT or some other theory; but no such event of this small duration has ever been observed. For sure, you and I can mathematically state that the sum of 10^100 time parts of 10^-100 seconds each equals 1 second exactly. but such mathematics is about a metaphysical problem; not a physical problem. And the "planck time" is such a metaphysical quantity. though I admit, one of physical interest.

Similarly Ethan's trillions of years; I consider metaphysical. It is part of the narrative of his particular interpretation of standard big bang cosmology; but it is not part of the observation of any current scientific theory. And Sobral et al's observations may force Ethan to change his big histories narrative a bit.

Observations constrain the big picture narratives by eliminating varies subtheories and those subtheories assumptions which can no longer be considered as reasoned.

And to think that a current scientific theory about the universe will still be standing when and if observations increase by 3 orders of magnitudes (i.e. Ethan's trillions) or by 25 orders of magnitude (Planck time) is vewry presumptuous. An awful lot of new physics can occur with even 1 order of magnitude increase in astronomical capability.

So that's where I draw my metaphysical line.

Metaphysics is that part of a narrative of a scientific theory which is an necessary assumption or an unfalsifiable extrapolation of a scientific theory.

Wow, where do you draw the line between metaphysics and physics?

OK, where did I call your asertion of metaphysical disparagement?

I called it wrong, not disparaging.

Just because Mystic Meg, the TV Astrologist makes a prediction that you can test doesn't make Astrology science.

This paper, as far as it has appeared to be so far, is little more than the proclamations that Israeli Air Force pilots produced more Girls than Boys.

I.e. an interesting point.

But devoid of context given it: that somehow genetics were being affected.

Same here.

Where did you make the statement other than just now that you were calling something metaphysics?

So how can it either be relevant for me to answer a question on this newly introduced and unanchored proposition, or for you to raise it as something I have mischaracterised, given that you only now just raised it?

OKThen,

I do not like your personal definition of metaphysics, in that you lump in predictions of theoretical physics that are impractical to observe with something that has nothing to do with physics altogether.

I think Wow has understood my point that I am arguing: Sobral et al. have discovered the leading term in the star formation density rate in our Universe, which is an interesting measurement. On a log-scale, a simple straight line (i.e., a power law) fits the data to this point. This is:
1.) not surprising,
2.) interesting that it was measured,
3.) likely very closely related to the rate of starbursts / major galaxy mergers, and
4.) likely to continue to follow this pattern for billions of years into the future.

But it is not likely that this is always going to be the dominant term. As galaxy mergers eventually cease (due primarily but not exclusively to dark energy), and as longer-lived main sequence stars die and return large amount of pristine gas to the ISM, and as galaxies continue to contain very large amounts of gas relative to their amount of mass in stars (the ratio is still greater than 1 in most late-type galaxies), other terms will take over as the Universe continues to age.

That's not metaphysics; that's theoretical physics. It's not to decry Sobral's result, it's to decry extrapolating Sobral's result as being the dominant term for ever and ever into the future, even as that term continues to drop rapidly. If you were (somehow) around when the Universe was 100 years old, would you conclude that the expansion rate was always dominated by radiation and always would be, and that the "orders of magnitude" into the future one would have to extrapolate to have matter dominance (and eventually, dark energy dominance if you knew of it) would no longer be physics?

Just because you won't be alive to see it doesn't make it any less physical.

Ethan's explanation reminded me of the Long Tail phenomenon in online marketing.
I think Ethan and Sobral are basically in agreement or at least not contradicting each other, only they're talking about radically different timescales and distances.

My question is: how long will the merged milky way/andromeda galaxy last? By that I mean will the galaxy have collapsed into a black hole due to gravity or is the angular momentum* such that it's still happily spinning around in for example the year 12 trillion (isolated from everything else due to dark energy)?

*) I'm not a physicist but I think this is the correct term here.

In my mind physics theories have domains of relevance outside of which predictions can not be tested. In my mind, those ideas of a physics theory that are outside of realm of prediction/testing may be very important ideas for a theory (e.g. the singularity of general relativity); but they are nevertheless metaphysics.

In my opinion.
Inside the event horizon of a black hole is metaphysics.
Outside the event horizon of the visible universe is metaphysics.

HAVING SAID THAT, the science of physics depends on these metaphysical assumptions (e.g. GR singularities, inflation before the big bang) and tests the theories built upon metaphysical assumptions by making predictions that can be tested in the visible universe; NOT BY TESTING PREDICTIONS OUTSIDE OF THE REALM OF OBSERVABILITY.

In my mind PREDICTIONS OUTSIDE OF THE REALM OF OBSERVABILITY ARE METAPHYSICAL.

Merriam Webster defines "Metaphysics 1) a division of philosophy that is concerned with the fundamental nature of reality and being and that includes ontology, cosmology, and often epistemology"

So the fact that metaphysics includes much of cosmology is not really a controversial point. Again I ask, Wow and Ethan where is your line between separating physics and metaphysics in cosmology? Where?

Please give me your clear definition.

As to the scientific merits of Sobral et al work, I think it is excellent work; but I defer to the opinion of his fellow professional astronomers. What is the professional reaction to their work to date. that I cannot check.

Projections can always be tested.

The thought experiment that led to SR required something moving at light speed or nearly.

We have tested the consequences of that projection to lower speeds. But at the time, the instruments were incapable of measuring it. Same with the precession of Mercury from GR.

But because a projection can be tested does NOT make it scientific. Just verifiable. And just because some scientific process cannot be tested today does NOT make it nonscience or metaphysical.

The model you have for that projection, if it is scientific, is a scientific projection, even if it can never be tested by humans.

What sobral here seems to have is an interesting scientific fact being projected as a scientific theory. It is no more scientific a theory than "The number of deaths of cyclists on the road has increased, therefore more cyclists will die next year than ever before".

A projection,but no more scientific than Roger Pielke's polynomial fit to climate data used to "predict" cooling "any time now".

PS His methods and science to reach that conclusion about the age of stars and the past abundance of events seems entirely scientific.

The projection is entirely statistical form fitting.

"Another central branch of metaphysics is cosmology, the study of the totality of all phenomena within the universe."
http://en.wikipedia.org/wiki/Metaphysics

"Definition of METAPHYSICS
1 a (1) : a division of philosophy that is concerned with the fundamental nature of reality and being and that includes ontology, cosmology, and often epistemology"
http://www.merriam-webster.com/dictionary/metaphysics

Ethan and Wow, if you don't like the definitions of "metaphysics"; then take it up with Merriam-Webster or Wikipedia. Cosmology is a part of metaphysics; this is how the words cosmology and metaphysics are still used and have been used since ancient times.

I agree that a larger and larger portion of cosmology is what we would call hard physical science and within the modern scientific tradition of observation and experiment, i.e. falsifiability. But still a lot of cosmology (including very technical mathematical cosmology) is largely narrative and descriptive and completely outside of the realm of falsifiability.

The history of great scientists motivated by philosophical and/or metaphysical ideas is a long and profound intellectual tradition. Two of the best known modern philosopher physicists are Einstein and Heisenberg. Einstein's search for a general relativity was motivated by "Mach's principle (or Mach's conjecture[1]) is the name given by Einstein to an imprecise hypothesis often credited to the physicist and philosopher Ernst Mach." wikipedia.

Heisenberg of course was very involved in the development of the Copenhagen interpretation of quantum mechanics. But there are other interpretations, "According to a poll at a Quantum Mechanics workshop in 1997,[13] the Copenhagen interpretation is the most widely-accepted specific interpretation of quantum mechanics, followed by the many-worlds interpretation.[14] Although current trends show substantial competition from alternative interpretations, throughout much of the twentieth century the Copenhagen interpretation had strong acceptance among physicists. Astrophysicist and science writer John Gribbin describes it as having fallen from primacy after the 1980s." such intrepretations are metaphysical alternatives.

Metaphysics is a word with an accepted definition. Many great scientist have no problem thinking philosophically and metaphysically and acknowledging the metaphsical assumptions and consequences of their best scientific idea. the interplay between science and philosophy is continuously at work; think Dirac's infinite sea; think anthroplogic principle, thinlk...

So again I ask; where do you draw the line between physics and metaphysics. Think about it.

It's kind of like asking where do you draw the line between biology and physics. There is not a hard line; it's a usage line. Biology deals with living things; physics with inanimate things.

It's kind of like asking where do you draw the line between psychology and physics. There is not a hard line; it's a usage line. Psychology deals with internal experiences; physics with external events.

It's kind of like asking where do you draw the line between mathematics and physics. There is not a hard line; it's a usage line. Mathematics deals abstract concepts (such as number, geometry, sets, topology); physics applies mathematical concepts to the external world.

I know economist who think everything is economics, physicist who think everything is physics, philosophers who think everything is philosophy, comedians who think everything is comedy. And they all do make a certain point from a certain professional narcissistic point of view (that's a joke).

“Metaphysics means nothing but an unusually obstinate effort to think clearly. The fundamental conceptions of psychology (or physics, or cosmology, or biology) are practically very clear to us, but theoretically they are very confused, and one easily makes the obscurest assumptions in this science (or any sciewnce) without realizing, until challenged, what internal difficulties they involve.”
― William James, The Principles of Psychology Vol 1

I'm going to make pancakes for breakfast now.

No, I'm taking up the fact that you introduced "Metaphysics" on the very same post as you blathered on idiotically about how calling something metaphysics (which you only just there did) wasn't saying it was bad.

I'm not arguing with Mirriam and Webster because they, very sensibly, haven't been talking complete bogshite on this topic.

You claimed something incorrect.

You were called out on it.

Then you segued on to "Oh, if you don't like metaphysics..."

BOGSHITE.

You are not going to push the error you made off by making out you were being persecuted for talking metaphysics. You're being called out for talking bollocks.

Just because you can test a prediction DOES NOT MAKE IT SCIENCE.

FUCK ALL to do with metaphysics.

Wow

You started the BOGSHITE when you said, "Sobrel may be making a scientific prediction in your opinion, but it’s no more scientific a prediction than mystic meg. Just because you can see whether she’s making accurate predictions doesn’t make her astrology predictions scientific."

I assumed (perhaps incorrectly) that your words, "mystic meg" , and "astrology" were sarcastic disparaging metaphors to my use of the word "metaphysics."

So I responded to your bollocks by saying, "To call a part of the cosmological narrative of the standard model metaphysics is not to disparage it."

Obviously, I was wrong; apparently you just wanted to insult Sobral et al's scientific work. And you were apparently referring to a real TV astrologers. I did not know; I don't watch TV astrologers. Sorry if I misplaced your disparagement. Do try to write in clear unambiguous sentences next time.

But it would be nice if your disparagment of Sobral et al's research was based on reading their paper. http://arxiv.org/pdf/1209.1396v1.pdf
Have you read Sobral et al's paper yet???

No, you started on the bogshite, OKThen.

When you proclaimed: "The statement “Every Galaxy will have New Stars for Trillions of Years!” is not a scientific prediction;"

And continued in that vein when you went on to say: "See right here Sobral et al are making a scientific prediction with the words,..."

Because you have the completely wrong idea about science and what prediction is telling you about it being science.

NOTHING.

Mystic Meg makes predictions on who will win the lottery.

NOT SCIENCE.

Weatherman makes predictions on the weather tomorrow.

SCIENCE.

Prediction tells you NOTHING about whether something is scientific or not.

YOU started with the bogshite.

Then wibbled off on "Oh, talk to the dictionary" for reasons which can make sense only in your deranged mind.

Nothing wrong with your comments here, OKThen.

"Prediction tells you NOTHING about whether something is scientific or not."

- Wow

If you drop a stone and it is going down, it is a "projection of an entirely statistical form of fitting.".

Newton would be ashamed, to do such a ridiculous assumption.

"In science, a prediction is a rigorous, often quantitative, statement, forecasting what will happen under specific conditions... Notions that make no testable predictions are usually considered not to be part of science... until testable predictions can be made." wikipedia

Wow
Please clarify your ideas.
Dare to educate (e.g. upon the place of prediction in science.)
Give your perspective and insight.
Put your tiresome and pointless venom aside.
Can you explain in clear civil language?
I am waiting.

Now go look up "superset" OKThen.

Here's another one for you:

All answers are replies, but not all replies are answers.

Mystic meg is making predictions based on non-rigour astrology.

Soberl is making predictions based on non-rigour (scientifically) curve fitting.

Ethan is making predictions based on rigourous fact.

Ah, yes.

But in my opinion that a notion (regardless of rigor in facts, theory and math) is not a scientific prediction; if it can't be tested. It is part of a necessary metaphysical assumption (e.g. cosmic inflation before the big bang) or of the interesting metaphysical narrative (e.g. the ultimate fate of the universe) of a theory of physics.

My opinion on this may not be yours or Ethan's; the notion of anything a trillion years hence is to me science fiction or metaphysics.

I accept your judgement that Sobral et al's work is based on "non-rigour curve fitting" and not as rigorous as Ethan;s thinking. And I also accept Ethan's conclusion that Sobral et al's work is " interesting that it was measured... likely to continue to follow this pattern for billions of years into the future."

But in my opinion, Sobral's et al's less rigorous scientific prediction fits solidly inside the tradition of the scientific method; whereas Ethan's prediction is outside the scientific method. And I might add that it is outside in a way that is unnecessary and unhelpful to the advancement of science.

Guth's cosmic inflation event before the big bang is a necessary metaphysical assumption upon which current cosmology can build a more precise cosmology (or not). i.e. does such an inflationary event set up and lead to a universe such as we observe or not and in fact lead to an imporved cosmology, i.e. one whose predictions about the observed universe are better than pre-inflationary cosmology predictions. Yes/ no?

Ethan's prediction of 1 trillion years hence is scientifically passive. It is neither a necessary assumption (e.g. Dirac's infinite sea of fundamentally unobservable negative energy particles); nor an necessary conclusion (e.g. one that can be tested and verified or not). Of what scientific use (other than metaphysical narrative) is the discussion of new star formation 1 trillion years hence; in a world where the oldest observed measurement is 13.7 billion years? (not a rhetorical question)

The 4 billion year hence collision between Andromeda and the Milky Way is a prediction that fits within the evidence of the 13.7 Billion years of the universe. Many galaxy collisions are recorded in the astronomical record. Galaxy collisions are within the domain of relevance of classical mechanics and classical astronomy.

1 trillion years hence is outside the domain of relevance of any science. not just astronomy. I don't think we have the scientific rigor in facts, theory or mathematical techiques to predict anything 1 trillion years hence. (by the way, the half-life of a proton as 10^32 years is a prediction about the stability of protons measured in the universe today (not a trillion years from now).

In my mind, 1 trillion years hence predictions are either
- metaphysical extrapolations that are scientifically unnecessary (regardless of rigor).
- science fiction
- predictions about something in the universe today (e.g. protons half-life of 10^32
- really necessary assumptions (e.g. in a cyclic universe, the future better set up the conditions of the past)

In my mind, an unnecessary conclusion (e.g. the ultimate fate of our universe, or even 1 trillion years hence) is not fundamentally, scientifically any different than an unnecessary assumption (e.g. god).

In my opinion, Occum's razor applies not only to unneccessary assumptions but also unnecessary conclusion (prediction). In my mind an unnecesary conclusion is one that neither becomes a necessary assumption nor becomes a testable prediction.

Here, the idea of a unnecessary conclusion not becoming a necessary assumption (I suppose is where your superset remark applies); but I'm not sure how or if we disagree. Perhaps you can help me? Tell me where my thinking is wobbly? or Just agree to disagree?

"But in my opinion that a notion (regardless of rigor in facts, theory and math) is not a scientific prediction; if it can’t be tested."

And your opinion is wrong.

This is fine. It's why science wins over religion.

A human CAN be wrong.

The Creator Of All Mankind? Oh, no, that's a sin!

Your opinion is wrong.

It's a useful yardstick, but it is really a nouveau-science abuse of the ancient ideas of Popper.

We don't use the same definition of life as they did in those days.

And it's not even correct.

Wait 1 trillion years. Or bequest it to your ancestors to check up on in a trillion years time.

Eminently testable.

"Testability, a property applying to an empirical hypothesis, involves two components: (1) the logical property that is variously described as contingency, defeasibility, or falsifiability, which means that counterexamples to the hypothesis are logically possible, and (2) the practical feasibility of observing a reproducible series of such counterexamples if they do exist. In short, a hypothesis is testable if there is some real hope of deciding whether it is true or false of real experience." wikipedia

Yes, I understand, "Every Galaxy will have New Stars for Trillions of Years!" is eminently testable.
We just won't know if this scientific hypothesis is correct or incorrect for trillions of years.

Rigorous scientific hypothesis testable in trillions of years versus
not so rigorous scientific hypothesis but testable and refinable every 5 or 10 years?

Hmm, it's a tough choice but I choose....
the next 100 iterative results and follow on refinements of Sobalt et al type hypotheses.

"We just won’t know if this scientific hypothesis is correct or incorrect for trillions of years."

"Every Galaxy will have New Stars for Trillions of Years" is NOT the hypothesis, OKThen.

This may be the root of your problems here.

The hypothesis is standard stellar evolution. The consequence is that every galaxy will have new stars for trillions of years. Because the mechanism for star formation and the availability of that mechanism does not seem to be ready to stop star formation.

As a CONSEQUENCE stars will continue to form.

Sorbel's statement is taking the hypothesis "If we fit the star creation rates to a curve and extrapolate..." then only 3% of stars remain to be born.

Hypothesis is not scientific. Conclusion is therefore not scientific.

Let's just keep it simple and quantitative, since that is what this post was supposed to be about, and realise that actually even in the media "version" the news are actually really quantitative/accurate. The findings mean that galaxies will, indeed have "new stars for trillion years", so, really, the arguments of this post are just a consequence of not reading the actual press release in detail/the actual paper and jumping into conclusions about this based on *some* press titles (but not contents). So let's be quantitative, show that Ethan's point is true and that it DOES NOT contradict the new results:

- Let's see if Ethan's point about the Universe producing new stars for trillions of years are consistent with the observed values and let's make something even better: let's quantify. Let's not just say "new stars", let's have a number for it (see details of the calculation below - here are the results):

-Let's start now, T=13.5 and take all stars formed from now to T=1013.5 (one trillion years into the future. So just take the integral of log(SFRD) = -0.14xT -0.23 (T is in billion years, but SFRD is mass of new stars per year per volume) and compare what the total number of stars predicted in a trillion years with those that exist today, per co-moving Mpc^3:

In a trillion years: 0.520 billion "sun-like stars"
Right now: 0.502 billion "sun-like stars"

In the next trillion years: *18 million more stars will exist* per co-moving Mpc^3 when compared to today; that seems a lot, but now do the ratio between then and now: what do you get? 3.6 % more stars. Now wait forever if you want to get close to the 5% increase mentioned. So Ethan, let's just be clearer about this; why not updating the title to : "the Universe will have millions of new stars for trillions of years!", then add *but that will never be 5% more than the current number of stars that already exist! :)

Notes on how to calculate this based on our observations:

- Currently, there are about 0.502 billion sun-like stars (I'm using 1 solar mass = 1 star, since ethan mentioned that there would be a certain number of stars born, not a certain amount of mass in stars born) for every cubic co-moving Megaparsec. Since most people here seem to be familiar with our own galaxy, they will soon realise that you can fit quite a lot of milky ways in a cubic Megaparsec (since our galaxy occupies something like ~300 kpc^3, so something 300 thousand times smaller than a cubic Megaparsec.

- Of course, most of the volume in the Universe is *not* occupied by galaxies, so the average cubic Megaparsec will not have that many galaxies (and that's why the average is about 0.5 billion stars per cubic Megaparsec).

- Good! So now we know something ver quantitative, widely measured and that we can use.

- Another thing we can measure: for a given average co-moving Mpc^3, how many stars are being born per year? This is what we have measured, using multiple large volumes at very precise look-back times (using the H-alpha emission line; quite widely used in our own galaxy and well-callibrated) so we can compare the evolution.

- The number of new stars per year per co-moving Mpc^3 is given by (completely based on *OBSERVED* values, no extrapolations): log(SFRD)=-2.1/(1+z), where SFR is in Solar masses per year per co-moving Mpc^3 and z is the redshift. If you prefer as a function of time log(SFRD) = -0.14xT -0.23, again SFRD in the same units, but T in billion years. So it's that simple.

Richard,

Got a mechanism?

We have one for the inundation in the solar system that peppered many solar system bodies with humungous levels of craters. We have explanations and mechanisms for why some of the bodies do not show craters, and in some cases, a different cratering pattern over different areas.

If you only have "looking at the stars created that we can spot..." you have correlation but no reason to predict that only 3% remain to be born. There's enough gas to create several orders of magnitude more stars to replace the ones we have.

Over the next trillion years, that pay be 3% replenishment rate, but a thousand times that you still have 30 times as many stars, making it 3% of stars or less have already been born.

In short, the claim: "If the measured decline continues, then no more than 5% more stars will form"

Begs the question: how do you know the IF will come true?

Really Ethan and myself are saying that that is not going to be the case.

You might as well say "IF wishes were fishes, we'd all cast nets".

True, but the condition is highly unlikely to be true. If it were, though, you bet we'd all cast nets.

You seem to be confused: I thought we were talking about actual measurements and what the measurements tell us. As a community we do have a few mechanisms that are responsible for this, but we are still working on really understanding which are most important:

- There is less pristine gas available now than 11 billion years ago
- It is harder for gas to fall into and cool down enough to form stars in galaxies now than in the past. "Beast"galaxies have very effective feedback mechanisms which prevents them to form new stars (read about radio-loud AGN mode), and even smaller galaxies have feedback mechanisms (such as supernovae) that can put a stop to star-formation by blowing up the gas

- Environment: as structure grows and galaxies fall into clusters/groups and dense regions, the quite violent physics happening there can really strip the gas and, even when you get a sudden "triggered" episode of star formation almost galaxy-wide, those tend to be very short-lived and feedbak mechanisms + physics of clusters are really effective at shutting them down permanently.

- "Mass" and the dark matter haloes of galaxies: it seems like both the mass and perhaps the "shape" of the dark matter haloes which dominate the gravity profile in galaxies also plays a role in this.

So the mechanisms are here for us to explore them - and that is what we are doing. The feedback mechanisms and the increasing difficulty of getting both the high-enough density and the sufficient cooling for gas to form stars is likely to be blamed.

Wow:

Come one, if you know that something has behaved in a particular way, every year, for the last 11 billion years, surely assuming that it will go on like that at least for the next few billion years is certainly more likely than saying (like you) that it will suddenly change its behaviour, unless *you* come up with an explanation of why it should suddenly change.

Are you going to invoke new physics? New processes that *only* come into place right now? You are the one that need to provide explanations and mechanisms, because you are the one saying that things are about/will change completely: that is the only way you can break an 11 billion year old trend.

Except that's not what you're doing, is it David.

Unless you're going to claim that the quote is incorrect or from the journalist not your work, 5% replenishment rate over the lifetime of a star still has around 30x as many stars yet to be born, not 3% left in all of eternity.

If a volcano erupts and you, 20 years later notice it hasn't done more than rumble since, you would NOT be right in claiming that at this rate of activity reduction, the volcano would be dormant within the next 5 years.

Even though that "trend" when drawn out that way would indicate it.

Gravity has behaved in a particular way for as long as we can see. So if it continues to bahave in the same way it has, tomorrow the "sun will be up again", and that will continue for a long time. Is that a crazy prediction? Of course you don't know when the laws of physics will change...!

But back to your argument :

"Except that’s not what you’re doing, is it David."

That was exactly what we did (just read the paper and a few good articles on that) - we measured the cosmic/Universe-wide average of the star-formation rate density at very different times in the history of the Universe. This is how much star formation is occuring in an average large volume of the Universe. And to get that we of course observed large volumes over completely independent regions of the Universe, each containing 100-1000s galaxies.

That was what we measured and we measured it for various look-back times.

No-one's talking about replenishments or lifetimes of stars here; we are talking about actual measurements; actual data.

If you want a vulcano analogy here's one: we have looked at sample of 1000 vulcanoes, traced back in time and measured their activity. The data clearly shows a decline in the average activity of the total sample, indicating that the Earth's vulcanic activity is now much lower than in the past. Based on that we could predict that the Earth's vulcanic activity will continue to decline in a certain amount. So just like the prediction is not valid for any single galaxy, it is not valid for any single vulcano. It is for the Universe as a whole.

Is that concept so hard to understand? The prediction is not a for a specific galaxy - you may well find a galaxy that will still increase in mass by a factor 10, even 30, but the global Universe-average will not do so, unless you can claim a change in physics. - that's all we're saying.

Main problem about the arguments here: timescales.

Obviously, if a phenomenon that takes place over 0.1s is measured over 0.01 s there is no way in hell you can actual understand/measure/make any prediction about it.

If you measure it for t>>>0.1s (say 1 year), then you start to have an idea. If you measure it for a billion years and you still have no empirical prediction ability over such thing you are clearly doing something wrong...

So your arguments about vulcanos and the Universe 100 years after the Big Bang are not applicable here. Star formation (even if you think about individual bursts/ individual star-forming regions) happens on timescales of ~million years, so obviously you need to have statistical data over a range >> 1 million years. A range of 11 billion years is a range of time which is 11 000 x larger than ~individual star-formation episodes, and that is why you can actually have an idea of what is going on.

That becomes even more so because we are not just looking at a single galaxy, but at statistical samples of 1000+ galaxies adding up to a range in time which is >10 000 times larger than the typical star-formation timescale.

That is why you can hope to make a decent empirical prediction.

That said, Wow, please make up your sophisticated theoretical model to give me an actual prediction. Things it need to reproduce for me to believe it:

- Evolution of the star-formation rate density
- Evolution of the stellar mass density

If it complies to both and get a completely different result then you should publish it right away in Nature and you'll solve all problems to do with galaxy formation and evolution.

But until then, stop arguing against A NUMBEr if you don't have another one to compare with.

How can you say that a number is wrong, if all you have are qualitative arguments?

David
Your explanation is excellent.
It brings the discussion back to theory and observation of our universe. And it convinces me (as a layman) that your research methods are very rigorous.

In my mind, you and your team have set a very high standard. Any theory based on first principles or higher order terms which will dominate the far, far future; must first be in agreement with the facts of astronomical observation that cover 11 billion years of our universes history.that is a very high standard indeed.

I have returned to my conclusion that Sobral et al's research is absolutely excellent research. I look forward to their follow on refinements of their research that take account of more and different observations, etc. etc.

David, may I ask one question.
Does your work shed any light upon the difference in near galaxies (i.e. near galaxies whose light was emitted in the last billion years) versus old galaxies (those whose light was emitted 9 to 11 billion years ago)? My question is: If you take a pile of data from galaxies of any particular type; can you tell which ones are old versus which are near? Or maybe the distribution of galaxy types is different for old versus near galaxies? So to speak does the fossil astronomical record, tell us clearly that galaxies have evolved over the 11 billion years of observed data in this or that way.

David, I am interested in understanding your answer, opinion, perspective. I have no intention in arguing with you. I just want to learn.

Thank you David for taking the time to comment on this post; and interpreting your teams research with us. Looking at David's home page http://www.roe.ac.uk/~drss/SOBRAL/Welcome.html I see that he is focused upon "understanding of how, when, why and by which mechanisms galaxies form and evolve." Excellent! I will be following your work.

My only criticism of your work David Sobral et al is that your actual research paper is quite unreadable (at least for a layman like me). Yet I know from your comments here that you David can express yourself very well at the layman's level (mine). I know that blog comments are not a research paper. But take a look at Ed Witten's research papers; he is a master of simply communicating the complex (in the abstract and introductions and throughout the technical technical detail of his paper) in a way that a layman like myself can understand. Read page 2-3 the introduction of his most recent paper a random example http://arxiv.org/pdf/1209.5461v2.pdf Al the best David, and thank you again for the education!

And thank you Ethan for bringing Sobral et al's research to us. It has been an education for me. I'd be interested in hearing any of your final thoughts. I have no arguments left. I know that among the best scientists (e.g. Einstein and Bohr) there are differences of opinion. And the important part of the scientific discussion is not who ultimately was shown to be correct; but that the discussion moved the science forward by challenging each scientist to defend there best ideas.

So yes, Ethan and Wow, i hope you have more to discuss with David. I will be listening.

Ciao.

David,

The thing that troubles me greatly about your conclusion -- and it should trouble you too -- is that if we're 95%+ through forming stars in the Universe, even as a large-scale average, it means that we are going to end up, as the age of the Universe gets arbitrarily large, with large gravitationally bound structures like galaxies, groups, and clusters, with very large amounts of hydrogen that never get locked up and burned in stars.

I recognize that's what you get by extending your SFR measurements arbitrarily far into the future, but that's exactly why I don't think they're likely to be right arbitrarily far into the future. Put hydrogen in a gravitationally bound structure for an arbitrarily long amount of time, and eventually it will all burn/fuse together, given gravity, the ability to radiate/cool, and time.

It may take trillions or even quadrillions of years to get through it all, but unless you have some way to eject it from the galaxy before you burn it, you're going to eventually burn it all.

Your extrapolation doesn't lead to that conclusion and has no physical mechanism to explain what all that hydrogen does instead, and that's the prime reason it's incredibly suspect to me.

I think your observations are robust and your measurement of the evolution of the SFR is quality, and it's reasonable to extrapolate it into the future. But -- just as any small effects don't become visible until they become large compared to a dominant, decreasing term -- I think extrapolating it infinitely far into the future, as you do, is fundamentally flawed.

If you do not, I'd be curious to learn what you think happens to that hydrogen that prevents it from eventually forming stars, even given an infinite amount of time.

Thanks Ethan for bringing that up: that's a much more interesting discussion and certainly something that is yet to be solved.

There are actually quite a few problems which state just that: why don't galaxy clusters, which have tremendous amounts of gas, form stars? How can massive galaxies, which can have non-negligible amounts of stars, prevent themselves from forming them?

From a purely observational point of view, it does seem like the scenario which you suggested is indeed likely to become largely spread, i.e., there will be enough gas to form stars in the future, but it simply will not be able to collapse + cool down enough to form stars in a significant way. Likely physical feedback mechanisms seem to result from AGN (radio-mode/maintenance mode) feedback (preventing massive galaxies to form a significant amount of new stars), cluster physics/mechanisms operating at high densities (ram pressure stripping) - which can particularly "kill" lower mass galaxies; and supernovae feedback (which for the smallest/lowest mass galaxies is argued to be able to almost fully expel the gas - along with potentially changing the profile of the dark matter haloes etc).

Excellent research is being done at all those areas, and evidence towards that keeps being accumulated (i.e., enough gas available, just physics preventing forming stars at very high rates), so these would certainly be worth a post here or elsewhere.

OKThen:

#Does your work shed any light upon the difference in near galaxies (i.e. near #galaxies whose light was emitted in the last billion years) versus old galaxies (those #whose light was emitted 9 to 11 billion years ago)? My question is: If you take a pile #of data from galaxies of any particular type; can you tell which ones are old versus #which are near? Or maybe the distribution of galaxy types is different for old versus #near galaxies? So to speak does the fossil astronomical record, tell us clearly that #galaxies have evolved over the 11 billion years of observed data in this or that way
#

We have also been looking at the differences in morphology of star-forming galaxies in the last 11 billion years (I'm not sure this is what you are referring to?). We find that for star-forming galaxies, disky/spiral galaxies are the majority and this changes relatively little across time. They tend to be galaxies like our own milky-way, forming stars at the "typical" rate at the time they are being seen. There are also merger and very irregular galaxies which tend to have much higher star formation rates relative to the epoch they reside in, but we also find that the decline in the cosmic star formation rate density *is not* a result of the reduction of merger activity, as was previously suggested many years ago and sometimes assumed as a given. That has now been demonstrated by a few other studies as well.

This is still something we are working on, and perhaps not very simple to explain (nor necessarily accurate in detail), but we are actually finding that at least statistically and if you compare like with like, the evolution over the last 11 billion years is relatively simple (to first order): most galaxy properties stay relatively unchanged. What does change significantly is the "typical" rate at which galaxies form stars - that continuously declines over the last 11 billion years.

I fully agree with your point regarding the "readability" of my/our papers, but I think it is hard to make them different since they are specialised journal papers. That said, I do try my best to communicate the results in simple ways with talks (e.g. the fabulous life of Mr Universe), popular articles/papers and other outreach activities (including a "crazy" history of the Universe as a drug addict who took dark energy that I wrote and that you can hear here http://soundcloud.com/once-upon-a-universe/confessions-of-an-energyholic). I/we should all do more on this though!

David,

The difficulty with physical feedback mechanisms is -- unless you can expel the unburned fuel from the galaxy itself (which is, as you correctly state, only true for tiny, isolated dwarfs) -- they will all extinguish over long enough timescales, meaning that you *will* eventually form stars.

As far as my knowledge of it goes, the science behind it is not really settled enough (or at least, I'm not knowledgable about it) to feel comfortable writing about it at this stage. My expertise is on large-scale structure formation, DM and DE, and Early Universe physics.

My hunch is that, as the SFR density drop below a certain threshold, the slope will change, either becoming constant or dropping at a much slower rate, drastically altering (upwards) the total number of stars as we allow t --> infinity. It may take much longer than trillions of years, but it's hard to envision a self-sustaining star-suppression scenario that last an infinite amount of time without expelling the gas. (And violent relaxation won't do it.)

I'll keep thinking about it, but if you know something definitive on the issue I'd love to be pointed in that direction.

"But until then, stop arguing against A NUMBEr if you don’t have another one to compare with."

You don't have to have a number of angels that can dance on the head of a pin to decide that someone saying "Six" is wrong to say so.

Your extrapolation of your data is merely that: extrapolation.

No physics behind why it should be so, and a lot to say that is bunkum: the mass of dust in the Milky way (or andromeda, or Black-Eye Galaxy, et al).

You can project that figure all you like, but if all you have is a curve and you're fitting it, then you're not any more scientific than Roger Pielke who keeps fitting polynomials to the global temperature and says "it will be cooling down soon!".

You're not as deliberately wrong as he is, since he knows why he's doing this.

David
Thank for your answer.

Ethan and David
Regarding your discussion. You seem to be in agreement; but there still is something missing in your understanding.

Let me offer my speculative hypothesis. Warning: I am an amateur and my speculation is completely bogus unless Ethan or David say it has some merit.

I defer to David Sobral and Ethan Siegel's opinion on MY SPECULATION. They are professional astronomers. I am an amateur. IF THEY SAY NOTHING ASSUME MY HYPOTHESIS IS COMPLETELY BOGUS

My speculation follows:
The problem is so much hydrogen is trapped forever in stars and galaxies and can never get out and form new stars.
So I searched and found that the problem might be EVEN BIGGER!!

Have the missing cosmic baryons been found? ,E. Behar, S. Dado, A. Dar, A. Laor, 2011 http://arxiv.org/pdf/1102.0201v1.pdf
"90% of the cosmic baryons remain missing in the local universe (redshift z ∼ 0)... , it suggests that the IGM of the local universe contains most of the currently missing cosmic baryons implied by big bang nucleosynthesis, the observed angular power spectrum of the cosmic microwave background (CMB) radiation and the Thomson opacity inferred from its polarization, but only ∼ 10% are present in the galaxies, galaxy clusters and UVO absorbers in the local universe."
YIKES, I did not know!!!

If IGM hypothesis is correct; then most of the universe's hydrogen is not forever locked in dead stars in galaxies; it is free floating in the IGM (intergalactic medium). and we didn't even know it was there.

So now the paradox of Sobral et al's research is even bigger. Why is "the “typical” rate at which galaxies form stars – that continuously declines over the last 11 billion years?"

If Ethan is correct and if even more missing cosmic baryons (i.e. hydrogen) has been found; then there may be some serious error in Sobral et al's research. But what kind of error?

I hypothesize that Sobral et al have made a very simple serious systematic error. Their data is biased in the following way. (David or Ethan can very easily confirm that my idea is completely bogus or a possibility).

The Sobral et al's data shows that "for star-forming galaxies, disky/spiral galaxies are the majority and this changes relatively little across time. They tend to be galaxies like our own milky-way, forming stars at the “typical” rate at the time they are being seen... (But) the “typical” rate at which galaxies form stars – that continuously declines over the last 11 billion years."
Why? Of course the data is correct; but is it somehow systematically biased? ditto the mathematical analysis.

I conclude yes, Sobral et al's data is systematically biased in the following way.
At a given period of time (now or 11 billion years ago) there is a range of galaxy luminosity; but faint spiral galaxies at 11 billion years are either not seen in Sobral et al's data or do not contain enough information to be part of his galaxy survey. And galaxies that are very active forming new stars are brighter than galaxies that are less active in forming stars. Therefore, the greater galactic distance, the greater is Sobral's data biased galaxies that are actively forming new stars.

Now I search and find this paper:
Constraining the Bright-end of the UV Luminosity Function for z ≈ 7 − 9 Galaxies: results from CANDELS/GOODS-South, Silvio Lorenzoni, Andrew J. Bunker, Stephen M. Wilkins, Joseph Caruana, Elizabeth R. Stanway, Matt J. Jarvis, 2012 http://arxiv.org/pdf/1210.8417v1.pdf
"The bright high redshift galaxy candidates we found
serve to better constrain the bright end of the luminosity
function at those redshift, and may also be more amenable to
spectroscopic conﬁrmation than the fainter ones presented
in various previous work on the smaller ﬁelds (HUDF and
ERS)." OK.

So I think that Sobral et al are systematically missing faint high redshift galaxy or systematically eliminating them because they do not have enough useful spectroscopic data. And furthermore, I think that there is plenty of new hydrogen in the IGM (intergalactic medium) to feed new galaxies formation of new stars. And I suspect that the actual star formation in galaxies in our visible universe may be flat or even increasing when the systematic biases are removed.

Thus despite Sobral et al's excellent research, the star formation rate of the universe is constant due to the continuous influsion of IGM hydrogen into galaxies. Thus Ethan's statement to me is possibly correct in that it restates the hypothesis that the actual star formation in galaxies in our visible universe may be flat or even increasing when the systematic biases are removed.

Obviously, better data (e.g. James Webb Space Telescope) will help determine if there is systematic bias. But I think that Ethan or David have enough data and insight to form an opinion on my hypothesis of systematic bias.

I defer to David Sobral and Ethan Siegel' opinion on this matter. They are professional astronomers. I am an amateur. IF THEY SAY NOTHING ASSUME MY IDEA IS COMPLETELY BOGUS.

OKThen:

One of the big points of the data we took over 5 years and using over 50-70 nights of some of the best telescopes in the World (and the point of using 3 different telescopes) is so that we would be equally sensitive down to something like Milky-way star formation rates (1-3 solar masses per year) all the way back to 11 billion years ago. That is why we have used the VLT (8-m) and observed very deep pointings at the highest redshift, but we also did very deep observations at all the other redshifts.

Compared to previous studies and other heterogeneous compilations this is actually one of the big differences in what we did: we really are comparing like with like, both because of the technique and selection we apply, but even down to the same physical star-formation rate limit of things we can see.

Also, even with completely heterogeneous compilations of studies, you can really completely exclude that the star formation rate of the Universe is constant. I don't think no-one would argue against the decline and its steepness either, regardless os the method that you use.

But, of course, you can argue about whether 11 billion years is anywhere representative to predicting the global system. Maybe it isn't.

But what if we had data on the Earth's weather all the way back to 4-5 billion years ago in multiple slices and with multiple baselines. It doesn't matter how we would fit it or not: wouldn't that be at least as powerful as any theoretical guesses that we may have about how it behaved and how it will behave in the future? Again, of course, if we have only registered patterns over the last 100 years of so and the system is more like 6 billion years old, of course there is little hope in predicting what it will do...

Also, Wow, if your arguments were close to what actually happens, then we would have seen it very clearly when we predict the evolution of the stellar mass density evolution (mass of stars that are in a given volume in the Universe) and compare that with observations from a range of teams and studies and that really do go down to very faint galaxies (in terms of their stellar mass). If we were missing a significant fraction of the total star-formation in cosmic volumes, then our prediction (over the last 11 billion years) of the amount of stellar mass per volume would be a significant under-prediction of what's actually out there.

The reality is that our measurements are able to predict what is actually observed in terms of mass of stars per volume as a function of time. Also, the method to measure "stellar masses" in galaxies is completely different from what we use for measuring star-formation rates in galaxies, so you would need to be quite imaginative to come out with a complicated range of systematics that could make both agree.

If my point was "you're missing stars" then you'd have a point, David.

My problem isn't with your measurements.

It's with extrapolating those measurements. The "IF" you propose is unsupported by any science.

IF Mystic Meg could see the future, she could predict the next winner of the National Lottery.

Though it is fully correct, it hinges on the IF.

Which has no support in any understood process and contra-indicated in many tests.

We only have the one universe, so we can't use other universes not following your IF to discard it.

I'm sure you have heard about empirical models right? Models which are not necessarily based on theory but that do a good job at describing and predicting certain phenomena. So you are saying empirical models are not science. I'm saying you're ignoring the bulk of what science is.

Science is always full of "If"s. Even fundamental things such as "if the laws of physics do not change with time", or "if space-time continues to exist has it does not". Nothing guarantees that's the case. And yet you and everyone else think of such If's as quite good assumptions.

A stupid data-collector robot goes on and measures the trajectory of the Sun for thousands of years at very different locations on Earth. It concludes that there is a period of about 24hours and on top of that a period of 12 months. It then predicts, assuming (IF!) that the system will continue to behave like it did in the last thousands of years, the positions of the sun, seen from each point on Earth, for the next thousands of years.

You say the robot is not scientific. I say he's doing great empirical science, with a testable prediction, which new observations can refine or refute.

And I'm sure you've heard about curve fitting as a non-science method of prediction, right?

You actually need a theory to explain the empirical model.

Go get one, tiger.

You need a theory to UNDERSTAND the empirical model. But you do not need a theory for it TO WORK.

That's the key difference. And of course, there are thousands of people working on UNDERSTANDING the observations, including our group. If someone had a fully successful theory to explain all of it already you would not be discussing this with me, but with that someone who had just won the Nobel Prize.

Baby steps, wow, baby steps. Measuring it first and understanding it later is often much better than the other way around: because it avoids so many human biases and people pushing to detect what they should be detecting.

Plus, if I had both the empirical model and the theory to fully explain it, I would be out of a job.

Except that there is no "WORK" there.

You're predicting the future, David. Until a lot of time has passed, there's nothing to say "This model is WORKING".

Dark Matter has similar problems, but at least people proposing it are considering different ways of finding out what the hell it is (i.e. proposing mechanisms and causations).

You don't need to fully explain it either (hell, we don't have a theory of GRAVITY fully explained), so stop with the strawmen there.

Have a theory that explains it AT ALL.

"Continuing the line to the future" isn't a theory. It's an activity. And one that has no basis to be accepted.

Rejecting the "If..." means your papers conclusion is falsified.

And currently you have NO REASON to accept the "If" presented.

It's that simple (to explain why I said it "works" - http://home.strw.leidenuniv.nl/~sobral/FIG3_G.jpg for the prediction and measurements comparison):

1) If you assume the star formation history we obtained, we can PREDICT the stellar mass density at any given time in the Universe. That means 11, 10, ... 1, billion years ago or at any time from 11 billion years ago. That is one of the things we did.

2) So let's test it. There are independent, high-quality data - so we CAN TEST THE PREDICTIONS. What about 10 billion years ago?
- Spot on.

3) What about 9 billion years ago?
- Spot on

... (and so on): see http://home.strw.leidenuniv.nl/~sobral/FIG3_G.jpg for the prediction and measurements comparison

n) what about now?
- Spot on.

Conclusion: at all times for which there are data to confront the predictions, the predictions pass the test. So it *works* (and this is what I meant by working). It predicts. It is tested. It passes the test.

Ok, so that does have (At least some!) some prediction power, because it makes clear predictions, it is confronted with completely independent observations, and it is able to predict the right values. So sure, maybe it will break down in a long, long time, but since it predicts the evolution of the stellar mass density really accurately over the last 11 billion years (80% of the total "life" of the Universe), and it is based on a continuous decline which is modelled using a really simple (it is not a far-fetched weird, complicated polynomial!) is it really that hard for you to at least consider the possibility that it may well provide a decent guess - based on what we know now?

David
Thank you. I'm sure your paper explained your research diligence in technical terms; but I do appreciate the layman's explanation. As I said, my hypothesis was an AMATEUR SPECULATION, a learning hypothesis. Thank you for taking the time to address my learning hypothesis and teach me.

Just to clarify: the "prediction" for the future is obviously not *AT ALL* a "conclusion" of the paper we are discussing. It is a mere curiosity. Something nice to play with and make an interesting guess.

The conclusions are measurements and the description of the evolution in the H-alpha luminosity function (which, by the way, are tremendously important and have high *prediction* power for new space telescopes currently being planned/built such as WFIRST and Euclid), the evolution of the star formation rate density and the fact that it predicts the measured evolution of the stellar mass density.

In many other papers we also interpret and discuss the several effects that are probably driving what we see, including the role of the environment, the role of galaxy mergers, the morphologies and disk dynamics, metallicity gradients, dust extinction properties, clustering and the dark matter haloes that host the star-forming population across time and many other key aspects.

When we do combine everything I'll let you know whether we get a nice and simple picture which supports or refutes the "crazy" extrapolation of the trend.

Wow

Which of Sobral et al's conclusions exactly do you disagree with?

Come on. I thought that you had a Ph.D in astronomy. If so, then engage David as a scientist about a specific problem with his conclusion. And I'm an amateur. For guidance take a look at Ethan's scientist to scientist conversation with David. Excellent, we all learned something if we were listening.

We are learning nothing from your protestations of what? What exactly is your point?

And what's up with your problem with empirical science?

Perhaps your view empirical science (experimental and analytic methods) as lower in the hierarchy of science than analysis based on first principles. e.g. " A calculation is said to be ab initio (or "from first principles") if it relies on basic and established laws of nature without additional assumptions or special models. For example, an ab initio calculation of the properties of liquid water might start with the properties of the constituent hydrogen and oxygen atoms and the laws of electrodynamics. From these basics, the properties of isolated individual water molecules would be derived, followed by computations of the interactions of larger and larger groups of water molecules, until the bulk properties of water had been determined."
Is that your point?

Wow says, "You actually need a theory to explain the empirical model. Go get one, tiger." Your insults express your ignorance not David's. Try to make a scientific point.

But David says, "Wow, please make up your sophisticated theoretical model to give me an actual prediction. Things it need to reproduce for me to believe it:
- Evolution of the star-formation rate density
- Evolution of the stellar mass density
If it complies to both and get a completely different result then you should publish it right away in Nature and you’ll solve all problems to do with galaxy formation and evolution.
But until then, stop arguing against A NUMBER if you don’t have another one to compare with."
So Wow get a number or point to research that takes Sobral et al's data an analyses it the way that you suggest.

But Wow you are a good enough scientist to understand the catch. There is no theory yet to calculate from. And no theoretical astronomer is going to do the extremely difficult calculation that you suggest (with todays theory) unless there is a possibility that there will be a significant prediction in the NOW of our visible universe that can be tested NOW or with the next generation super James Webb space telescope (next 100 years). Because if Sobral et al's curve fitting is as good as it gets prediction wise for the next billion years of observation; a good theoretical astronomer will do research whose predictions can be verified or not in the today (next century or less).

As Ethan said to David "I think your observations are robust and your measurement of the evolution of the SFR is quality, and it’s reasonable to extrapolate it into the future."

So in my mind, if I accept Ethan's problem is correct; then in my mind there has to be some physics that we can understand today that suggest, aha here is how that hydrogen trapped in stars and galaxies gets out. e.g. this is the untrapping principle. But without understanding an untrapping of hydrogen principle; Ethan and Wow's first principle a concern is just a hunch.

As Ethan said, "My hunch is that, as the SFR density drop below a certain threshold, the slope will change, either becoming constant or dropping at a much slower rate, drastically altering (upwards) the total number of stars as we allow t –> infinity. It may take much longer than trillions of years, but it’s hard to envision a self-sustaining star-suppression scenario that last an infinite amount of time without expelling the gas. (And violent relaxation won’t do it.)"

So agreeing with Ethan's hunch and making it a specific quantifiable conjecture and then doing some math is just another form of "curve fitting as a non-science method of prediction"; if by "non-science" you mean we don't understand some first principles (e.g. the untrapping of hydrogen from dead stars principle).

Personally, it is my opinion that "science" never understands in the ultimate detail "first principles."

Sometimes empirical science is better science than our best first principles science.
- science doesn't get to the point of first principle analysis and understanding until after an awful lot of empirical science.
- even after a lot of empirical science, first principle science may be too difficult to do, e.g. Robert B Laughlin, 1998 nobel prize in physics points out, "it is presently too difficult to calculate from scratch which crystalline phase of ice will form at a given temperature and pressure."

So we need the empirical tables of data and extrapolations. And extrapolating Ethan or your hunch to a trillion years is worse than Sobral extrapolating about current observations and star data over the 11 billion years of empirical observation.

And by the way the phases of the universe, galaxies, stars, and planets are a whole lot more complex than the the phases of water.

So Wow are you a Ph.D. astronomer or not. Because you really sound worse than an amateur. So zip it or engage Sobral as a scientist, rise to the challenge; THINK, EDUCATE, DARE TO CLEARLY EXPRESS YOUR BEST IDEA.

This is clearly spin from the liberal media. We will never hit peak star. You are just trying to frighten consumers so they use their star-powered vehicles less and get on trains the run on steam.

You really make it seem so easy with your presentation but I find this matter to be really something which I think I would never understand. It seems too complicated and very broad for me. I am looking forward for your next post, I'll try to get the hang of it!|

Greetings! Very helpful advice in this particular post! It is the little changes which will make the largest changes. Many thanks for sharing!|

If it's true that star production will cease in ONE trillion years from today than the steady star production decline in the universe would have to come to a halt in 100,359,696,906 years after today and only a single star would form between then and 1 trillion years after today. If instead it's true that star production will cease in 100 trillion years from today than the steady star production decline would have to halt in 119,594,696,906 years after today and there would only be a single star formed between then and 100 trillion years after today.

I corrected my previous figures which were wrong. Here are the correct figures based on rate of star formation decline over last 5 billion years for star production in milky way galaxy. which is the best one to use because elliptical decline faster than ours. In reality it's going to decline slightly slower than rate of the last 5 billion years in milky way but assuming it was same rate of decline for Star formation rate in milky way then there are 2 answers. The final star formed cannot be later than 236,457,009,019 years from now because the next one wouldn't be until 100 trillion years after today, OR it is the final star produced is in 217,552,815,151 years from now because any later and the next one wouldn't be until after 1 trillion years from now. In reality of course it would be slightly later than these dates as star formation rate will decline a bit more.

It seems to me that decrease in star formation in the universe may be more about galaxy collisions and interactions dispersing the stars in galaxies creating elliptical galaxies with little or no star formation than using up all of the hydrogen.

Messier Monday: The Pleiades, M45

esiegel — Mon, 29 Oct 2012 16:32:08 +0000

Messier Monday: The Pleiades, M45

"Something there is more immortal even than the stars,
(Many the burials, many the days and nights, passing away,)
Something that shall endure longer even than lustrous Jupiter,
Longer than sun or any revolving satellite,
Or the radiant sisters the Pleiades." -Walt Whitman

Last week, we kicked off our very first Messier Monday by spotlighting M1: the Crab Nebula. But with 110 different objects to choose from, the Messier catalogue represents some of the brightest and most universally accessible wonders of the night sky.

Image(s) credit: SEDS -- http://messier.seds.org/.

Many of these objects are more easily visible at different times of the year; as we begin to approach the December Solstice, the ancient constellations Orion and Taurus become more and more prominent in the night sky.

Image credit and copyright: David Blevins.

The constellation of Orion and the nearby bright orange star, Aldebaran, are perhaps the easiest objects to identify (other than the Big Dipper) in the skies at this time of year, and are able to guide you to the Crab Nebula in the constellation of Taurus. But, believe it or not, that constellation contains only two Messier objects! The other one is the famous -- and oft-visible to the naked eye -- collection of stars sometimes known as the Seven Sisters: the Pleiades.

Image credit: The Amazing Sky by Alan Dyer; annotations by me.

The Pleiades -- or Messier 45 -- are most easily found by drawing an imaginary line from Orion's belt, past Aldebaran, and on to a fuzzy, cloudy collection of blue stars clumped very closely together.

To someone with very good vision and even reasonably good suburban seeing conditions, seven individual stars are clearly identifiable. Through even binoculars, it's clear that there's something impressive that goes beyond what our eyes can see.

Image credit: The University of Manchester / Derekscope, with the Moon from a 2009 conjunction.

The stars are clearly very blue, and there are clearly more than seven of them. But just how many more are there? To someone with a powerhouse piece of equipment, it becomes clear immediately that there's a treasure trove of beautiful, bright blue stars shrouded in dust just beyond the reach of our vision.

Image credit: Marco Lorenzi of Astrosurf.

There are over 1,000 confirmed stars in this young cluster of stars; under ideal conditions up to 14 of them can be seen with the naked eye. The hottest, brightest stars in there are B-class stars, which tell us that this cluster, although young, has actually been around for quite some time: at least 80 million years. The highest mass stars burn through their fuel the most quickly, and die in catastrophic supernovae explosions, leaving behind black holes and/or neutron stars.

There are plenty of O-class stars (the brightest type) in the night sky, and star clusters like the Pleiades -- open star clusters -- are the places where they're most commonly found. But we don't find them in the Pleiades! The lack of ultra-high-mass O-stars, and even a lack of the very brightest B-class stars, tells us that star formation ceased no later than 80 million years ago. (The brightest B-stars are type B0; the dimmest are B9. The only B-stars left in the Pleiades are B6 and dimmer.)

Image credit: the 10 brightest stars (including one binary) in the Pleiades, via Wikipedia.

But what we find, instead of O-and-bright-B-stars, is something quite remarkable, once we're willing to look with X-ray eyes!

Image credit: Thomas Preibisch, Würzburg (Germany), and the ROSAT X-ray satellite.

A huge number of X-ray point sources -- which typically identify black holes and/or neutron stars -- are a smoking gun of stars that have gone supernovae since the formation of the cluster, and have left behind degenerate stellar cores! The green boxes indicate the seven brightest optical stars, and as you can see, they don't have very much in common with the X-ray sources. (The ones that do may, in fact, be in binary systems!)

But you'll also notice -- far more prominently -- a slew of big, bright X-ray sources, many of which are hot (false-colored blue), and indicative of intense X-ray-emitting sources.

Know what powers an X-ray-emitting source?

Image credit: Robert Gendler of http://www.robgendlerastropics.com/.

Dust! Specifically, dust, gas, and other matter that gets accelerated by a degenerate objects like a black hole or neutron star. Magnetic fields in these locations are some 10¹⁵ times stronger than the magnetic field at the surface of the Earth, and when they get fed, they accelerate that matter and spit it out. But charged particles moving in a magnetic field emit radiation; in these cases, the radiation is so energetic that we see it as X-rays!

And while the dust itself is quite prominent in the visible part of the spectrum, the way to really get a window on it is to look in the infrared, where neutral, warm gas and dust dominates.

Image credit: NASA/JPL-Caltech/J. Stauffer (SSC/Caltech).

The Spitzer Space Telescope shows us, quite clearly, that there's no shortage at all of this gas and dust in the neighborhood of the Pleiades.

Over time, the remaining B-type stars will burn out, and since they're not quite massive enough to create supernovae, they'll form planetary nebulae and white dwarfs when they do. The dust will continue to evaporate and will eventually be either ionized or blown into interstellar space, as this evaporating dust cloud near Merope -- courtesy of the Hubble Space Telescope -- is doing.

Image credit: NASA and The Hubble Heritage Team (STScI/AURA).

Eventually, this great cluster of stars will -- over hundreds of millions of years -- be torn apart into individual stars and much smaller groups by gravity.

But for right now, we've got an amazing collection of over 1,000 stars just 500 light years away from us, helping light our night sky with a spectacular display.

Image credit: Geert Vandenbulcke of http://www.astronomie.be/.

That's one of the nearest open clusters to us and one of the most famous non-comets in the night sky: the Pleiades!

esiegel Mon, 10/29/2012 - 12:32

Tags

The Pleiades are also known as the name of a Japanese car manufacturer. Yes indeed, Subaru. The significance of the name relates the the seven or so companies that form Subaru.

Great article again Ethan. Thanks. But the image of Pleiades and Moon is from Stellarium or something similar. No way is that an actual photo, one clearly sees pixelation on the moon, it's a bitmap sprite, the exposure of the background is wrong also. If I were to bet my money, I would say Stellarium.

SL, digital cameras make an image composed of pixels.

I believe you mean "the image edge of the moon is made up of coarser pixels than the image itself", though this could be a result of composite picture, which would HAVE to be done to get the moon and the dust cloud the Pleiades are going through illuminated visibly together.

The biggest idea for it being a simulation is the lack of stars in the field whilst exposing enough to show the aforementioned dust.

@Tony P:
Actually it was six companies that formed Fuji Heavy Industries (former name of Subaru):

http://www.subaru-global.com/origin_name.html

Note the Subaru logo has six stars.

It seems to me in any case that there are six most easily visible stars in M45, and if you can see seven, you can probably see more than seven.

Nick

Siniza & Wow,

I was suspicious of the image, too. Here is the site where I retrieved it from: http://www.derekscope.co.uk/2010/02/the-moon-and-pleiades-seven-sisters/

Although it asserts that this is an actual image, I know of no filter that would successfully reduce the brightness of the Moon that much while exposing the Pleiades that well. At the very least, it's a composite, and at the most, it's entirely simulated.

Another treasure, Ethan. Thanx.

Did some checking on net.. :) It's a fake, and even a wrong fake at that :))))

Here is the original

http://www.jodrellbank.manchester.ac.uk/astronomy/nightsky/nskyoct09.ht…

the image is from Stellarium, and it's for 7th of October 2009! :))

Guess Derekscope doesn't know the difference between astrophoto and stellarium :) It was made by manchester guys, but only with "printscreen" :)))

Thanks, Sinisa.

Looks like I'll be thinking twice before I take images (and captions) from Derekscope again. Also, well-done on the intuition that it was generated with Stellarium!

It's a risk when using google search for images.

Good sleuthing, Sinisa. I got only as far as confirming that there actually was a lunar-Pleiades conjunction on Oct. 7, 2009, just as Derekscope saide. The difference in pixillation of moon and stars was pretty solid evidence of a mashup, but I couldn't find definitive proof. Well played, sir.

Thanx guys :) Pleasure to be able to contribute at least a little. I learned so many new things here, if I can give anything back, that's great :)

See, I looked at that image and just assumed the moon was placed in the image for scale.

Hi everyone,

I have a question that is completely unrelated to this post. I was reading an article today about the oldest supernova ever detected, almost 12 billion light years away. Here's my question...I am having trouble understanding how the light from a supernova that occurred only 1.5 billion years after the Big Bang is just reaching us now. If this supernova happened only 1.5 billion years after the Big Bang, when both our sun and the earth hadn't been formed yet, how is it that we are still able to detect it? It seems to me that this light should have dissipated long ago. Along the same lines, I don't understand how we are able to see the first galaxies ever created. Again, shouldn't this light have passed us by billions of years ago? I would much appreciate someone enlightening me in my ignorance.

If it took someone to send the message of your birth to another person 30 years, and that person hadn't been born yet, the message can still get to them 30 years later when they are.

Nice article again, Ethan, thank you so much.
Has anyone pondered on the effect (if any) all the supernovae explosions you mention after showing us the X-ray image, occurring that close to us (500 ly), may have had on the life on Earth?

This was one of the first astronomical objects I viewed through my dob, it was also the first moment that I experienced such a profound sense of scale in regards to space. I'll never forget that moment; it changed my life.

When we see light from stars (including our Sun), we are seeing these stars as they looked like in the past; that is to say, light from a supernova 12 billion ly distant, took 12 billion years to reach us! Incidently, most cosmologists believe that, shortly after the big bang, space expanded very rapidly - much faster than the speed of light during a period called "inflation", which makes most of the Universe unobserveable, given the finite speed of light.

Get Your Galaxy in Gear!

esiegel — Fri, 17 Aug 2012 16:26:50 +0000

Get Your Galaxy in Gear!

"We don’t understand how a single star forms, yet we want to understand how 10 billion stars form." -Carlos Frenk

The Universe has been around for a long time: nearly 14 billion years, to the best of our knowledge. When it was very young, there were absolutely zero stars in it, while today, there are hundreds of billions of galaxies, each of which contains anywhere from a few billion to many trillions of stars.

Image credit: NASA, ESA, and the Hubble Heritage (STScI / AURA) - ESA / Hubble Collaboration

The galaxy shown above, NGC 2841, is very similar to our own Milky Way. Approximately the same size and shape, this massive spiral is full of dust lanes, flocculent arms (with multiple branches), a central bulge, and perhaps the only major apparent difference is there's no central bar like the Milky Way has. But one other important thing this galaxy has in common with our own is a very low rate of star formation.

How can you tell how quickly a galaxy is forming stars? Compare the spiral above with the Whirlpool Galaxy, below.

Image credit: NASA, ESA, S. Beckwith (STScI), and The Hubble Heritage Team (STScI/AURA).

The beautiful grand-design spiral (with two big, sweeping, wrapping arms) also has lots in common with the Milky Way, but its star formation rate isn't one of them. You don't need to be an expert in star formation, either, to know this: all you need to do is look at the colors in this galaxy.

See all that pink in those spiral arms?

Image credit: NASA, ESA, S. Beckwith (STScI), and The Hubble Heritage Team (STScI/AURA).

That's your evidence for star formation! No, really, it is, even though it might seem a little counterintuitive.

To understand this, let's take a close look at the largest star forming region in our local group of galaxies: the Tarantula Nebula in the Large Magellanic Cloud.

Image credit: Volker Wendel and Bernd Flach-Wilken.

First off, you'll notice it is that same red/pink color I showed you along the Whirlpool Galaxy's arms, but you might wonder why that's so.

After all, it's not like the hot, blue, newly-formed stars powering it give it that blue color, right? Let's take a look at the core of the Tarantula Nebula, where two star clusters, each containing hundreds of these hot, blue stars, are in the process of merging together.

Image credit: NASA, ESA, & F. Paresce (INAF-IASF), R. O'Connell (U. Virginia), & the HST WFC3 Science Oversight Committee.

These stars themselves, although relatively short-lived, are far bluer than our Sun is. Yet, believe it or not, that's exactly where the secret lies!

The hotter a star is, the bluer it appears to us, because it emits relatively more blue light than red light. But the spectrum of light emitted by a star goes oh-so-much farther -- in both directions -- than what our eyes can perceive. And for these hotter, bluer stars, the vast preponderance of that energy gets emitted in ultraviolet wavelengths.

Image credit: Pearson Education / Addison Wesley.

With all that ultraviolet light, the atoms in the surrounding gas -- which are mostly hydrogen, remember -- become ionized, as the ultraviolet light is powerful enough to kick the electrons in these atoms off of their nuclei.

But there are well over -- are you ready -- 10⁶⁰ hydrogen atoms in every known star-forming region, meaning that each electron is incredibly likely to run into a hydrogen nucleus in short order, forming neutral hydrogen once again.

Image credit: Hyperphysics at Georgia State University, http://hyperphysics.phy-astr.gsu.edu/hbase/hyde.html.

And when that happens, the electron drops through the hydrogen atom's discrete energy levels, emitting a very characteristic red line (at 656.28 nanometers) and that's what turns the regions of space where new stars form red! (Or pink, when combined with the underlying white/blue-white starlight.)

Here's maybe another familiar star-forming region -- the Eagle Nebula -- but presented in the same colors that the human eye would perceive it.

Image credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona.

Despite the Eagle Nebula, above, being located within our own galaxy, it still forms less than one star-per-year, on average. In fact, the entire Milky Way, when all the star-forming regions are summed up, forms only about one new solar mass' worth of stars each year. (See here for some gory details.)

But this hasn't always been the case, either for our galaxy or many of the other quiet ones, which we know just from counting.

Image credit: Gigagalaxy Zoom project, ESO / S. Brunier.

There are about 200-400 billion stars in the Milky Way, while the Universe itself is less than 14 billion years old. If we only formed about one star-per-year over the history of the Universe, our galaxy would only have about 5% of the stars that it actually does!

So something must've been different long ago to form all the stars we currently have. And we can figure that out by looking at galaxies with much larger star formation rates today! What do those galaxies look like?

Image credit: Immo Gerber and Dietmar Hager, Tao Observatory.

There are galaxies, like NGC 660, above, where practically the entire galaxy is a star-forming region, which makes it known as a starburst galaxy. This normally happens when a galaxy interacts with another one gravitationally, either swallowing a smaller companion, passing nearby a large gravitational source, or, in the most extreme case, going through a major merger.

Prior to this week, the most spectacular starburst galaxy we knew of was this giant monstrosity at the center of the Perseus Cluster.

Image credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration. Acknowledgment: A. Fabian (Institute of Astronomy, University of Cambridge, UK).

A smaller, fast moving galaxy is in the foreground, just maybe 200,000 light years (twice the diameter of the Milky Way) away from the central giant galaxy, and you can see the great pink regions indicative of star formation in here. But although the star-formation rate in this galaxy is huge -- maybe 40 times the rate of our own galaxy -- the central, active black hole causes the gas to get too hot to form stars too rapidly. Otherwise, the star formation rate could have gotten up to hundreds or even maybe a thousand times what our galaxy gets, but galaxies at the centers of clusters, with their supermassive black holes and hot, active cores, seem to forbid this.

We've thought that this was a limitation of large galaxies in general for a long time, and this was a spectacular example from a galaxy more than 200 million light years away. But there's a new record-breaker in town, and for once, this observation solves some previous problems!

Image credit: X-ray: NASA / CXC / MIT / M.McDonald; UV: NASA / JPL-Caltech / M.McDonald; Optical: AURA / NOAO / CTIO / MIT / M.McDonald.

The newly discovered Phoenix Cluster, located over 5 billion light-years away, has many of the same properties: it's a huge galaxy with a large central, supermassive black hole. (For comparison, it's maybe 5,000 times as massive as our galaxy's supermassive black hole!) It emits intense X-rays, and it definitely counts as an active galaxy.

But unlike all other known galaxies at the center of clusters, the core of the Phoenix Cluster has a star formation rate that rivals the fastest known star forming regions in the Universe, forming over 700 stars per year in the central region!

Illustration credit: Chandra X-ray Observatory.

Before this discovery, it was a little bit mysterious how the central cores of giant galaxy clusters got as large and massive as they are, given how these active, supermassive black holes seemed to forbid star formation. But this new discovery shows us that it is not forbidden!

So if you want to kick your galaxy's star formation rate into high gear, just feed it a gravitational source, and not only do you get a spike in newly formed stars, but even the biggest behemoths in the Universe aren't always immune from it. And this is a huge discovery as far as explaining how giant galaxies at the cores of clusters get to be so big, massive, and full of stars.

And obviously, there are more stories and angles here than I'm capable of covering in just the few articles a week I manage to put out. While I'm always happy to give you the science behind the biggest stories happening in the Universe, sometimes it simply comes out faster than I can write about it. But the Universe is such a wonderful place, I don't want you to miss a thing, so I've set up something I think you'll truly love: a way for you to stay on top of all the latest stories about Outer Space from around the entire world!

Image credit: http://trap.it/.

Meet the Outer Space trap, a real-time collection of news content -- updated continuously -- that ranges from news within our own Solar System to the furthest reaches of the Universe. And it gets my seal of approval, because I made it myself. There's far too much for me to cover it all, but that doesn't mean you should miss any of it, so I've done my best to bring you the best in content from every reasonable, reliable source of information out there. Follow @TheSpaceTrap on twitter or join the facebook community, because I want to give you every opportunity to learn about all the wonderful things we're learning about the Universe. And whatever you do, don't ever stop learning or abandon your sense of curiosity about what's out there and how it all works; I'll keep doing my best to bring it all to you!

esiegel Fri, 08/17/2012 - 12:26

Tags

Very nice and exciting.

But what am I missing?
- the Milky Way has 300 Billion stars, the Phoenix Cluster has 3,000,000 Billion stars, i.e. 10,000 times more stars than the Milky Way
- the Phoenix Cluster's supermassive black hole is 5,000 times more massive than the Milky Way galaxy's supermassive black hole!
-The Milky Way forms 1 star per year; the Phoenix Cluster forms 740 stars per year

So I would expect that if the Phoenix Cluster was forming stars at the rate of the Milky Way galaxy that it would form 5,000 to 10,000 stars per year not 740 stars per year.

I need a comparison between the "central region of the Phoenix Cluster" compared to the Milky Way galaxy;
OR between the "whole Perseus Cluster" to the whole Milky way galaxy;
OR something else (e.g. a best guess big picture story)

Otherwise I've just got a hot spot in the whole Phoenix Cluster that on average may be forming stars faster or slower than the Milky Way.

I'm not arguing with these great observations of a star formation hotspot; I just need the big picture story a little clearer to put these observations in proper perspective.

I'm not sure what you mean by: "explaining how giant galaxies at the cores of clusters get to be so big, massive, and full of stars." Presumably they're big Even before the stars form - just that the mass isn't in the stars yet.

You need dust to form a star. They don't meet up in psirs and have little baby starlets

@ Angel Gabriel:

Why would you expect there to be a linear relationship between SMBH mass and star formation rate?

@ William:

Yes but all those things need to be explained. How does they get so big, and how do they form all of those stars (while stars require a large mass of dust, a large mass of dust does not imply rapid star formation).

@ Gabriel

Oh, I think I see. The thing is star formation rates aren't constant, and both Milky Way and Phoenix must have had much higher star production rates in the past to reach their current counts in the time the universe has been around.

star production in globular clusters is very low.

Why?

Because they don't have a lot of dust left over.

Same with elliptical galaxies.

Same reason why all the new star formations are in the ARMS of the spiral galaxies (that's where the dust is).

Another Trip Around the Sun

esiegel — Fri, 03 Aug 2012 10:24:22 +0000

Another Trip Around the Sun

"How old would you be if you didn't know how old you are?" -Satchel Paige

Today marks another year and another trip around the Sun for me. For you, and me, and everything on Earth that makes it through another year on this world, there's a whole lot we get to experience.

Image credit: NASA / ISS Expedition 13.

Some things are tiny: the Earth's rotation slows by about two millionths of a second each year, while some are large: we hurtle over 900 million kilometers in outer space as we orbit around the Sun. Our Earth spins just over 366 times on its axis, while our one revolution around the Sun leaves us with 365 (and an occasional 366) days in a year.

But looking beyond the Earth, practically everything you can imagine in the Universe has undergone a lot in the last year you've been on Earth.

Image credit: NASA, of Tracy Caldwell Dyson, via Wayne Hale.

Every satellite we've put up, including the vaunted International Space Station, races around the Earth as we go about our daily lives. The low-Earth-orbit ones (like the ISS) race around the Earth at speeds around 17,000 miles-per-hour (27,000 km/hr), meaning that over the course of a year, they orbit the Earth around 6,000 times.

But while our Solar System is full of interesting facts and motions, everything I've mentioned and much, much more hurtles around the galaxy -- imperceptibly -- as the years unfold.

Image credit: Josch Hambsch's CCD Imaging, additional processing by me.

The entire Solar System speeds through the galaxy, traveling 7 billion kilometers each year in our Sun's journey through the galaxy's disk. But life goes on in the galaxy over that time, as gas clouds contract, forming new stars all the time.

Image credit: T. A. Rector & B. A. Wolpa, NOAO, AURA.

Each year, ~~around a million new stars~~ about a Solar Mass's worth of stars (reference here) form in the galaxy, mostly in star forming regions like the Eagle Nebula, above. At the same time, stars in our galaxy burn out and die, but not quite at the same rate.

Image credit: http://astrojan.ini.hu/, retrieved from Margaret Hanson, U. of Cincinnati.

Stars die spectacularly throughout the galaxy, but the vast majority of stars we form have a lifetime that's far greater than the present age of the Universe. As a result -- even optimistically -- only dozens of stars die each millenium in our Milky Way, meaning that each year that passes marks an extra new star or so in every galaxy in the Universe.

And those galaxies, themselves, are different on this day than they were even a year ago.

Image credit: Rogelio Bernal Andreo of Deep Sky Colors.

The nearest large cluster of galaxies -- the Virgo Cluster, above -- has around 1,600 large, Milky Way-sized (or larger) galaxies in it, and lives just 53 million light years away. It's also speeding away from us at over 1,200 kilometers per second, meaning that each year that goes by sees that entire cluster wind up another 40 billion kilometers farther away from us.

In fact, if you lived to be 229, you would find this cluster an extra light year distant from us than when you were born. But that's for the closest cluster of galaxies to us; what about the farthest galaxy we've ever discovered?

Image credit: NASA, ESA, G. Illingworth and the HUDF09 Team.

The light from this galaxy -- found in the Hubble Ultra Deep Field -- took 13.1 billion years, or 96% of the age of the Universe, to reach us. But the Universe is expanding so quickly that each year that passes sees this galaxy more than two extra light years distant from us! Even if we launched a spaceship today at 99.999999999%+ the speed of light at this galaxy, it would never reach it. As each year passes, maybe 20 or so galaxies newly suffer this fate: that they become unreachable, even in theory, from our place in the Universe.

So happy birthday to me and everyone who shares another year on the planet with me, and may the Universe continue to amaze and educate us all.

esiegel Fri, 08/03/2012 - 06:24

Tags

Happy birthday! If only more stars like YOU were born on our Earth... at least one a decade please?

Happy Birthday!

Happy B-day Ethan and all the best. Keep up the good work and live long and prosper! ;)

What can I say - You made many things much more understandable. And much more interesting for a layman. Thank You and keep up a good work.

Best regards.

PS Strange thing: 4 comments and another one from Poland :-) .

"...each year that passes sees this galaxy more than two extra light years distant from us!"

Does this mean that this galaxy is receding from us at twice the speed of light? If so, then how can we see it?

Did I miss something here?

Happy birthday! I hope it is a wonderful occasion.
:)

Happy birthday. And I'm as mystified as Jockaira (and an RAH fan)

I agree Jockaira,
I must have missed something too.
That implies that both our galaxy and this distant galaxy are relatively, each moving away from each other at faster than the speed of light.
Could someone please enlighten me?
Nice reflective blog though!

"Just remember that you're standing on a planet that's evolving; revolving at 900 miles an hour." - M. Python
Here's to one more time around for all of us!

Many more happy returns of the day.

Happy birthday, and best wishes for your next trip with the Earth around the sun!

(Aren't our galaxy and this distant galaxy apparently receding from each other at above the speed of light because the movement in part results from the distance between them increasing with the universal expansion of space? I know objects can't exceed the speed of light, but I believe the universe as a whole is exempt.)

Happy birthday, Ethan, and thank you for giving us this wonderful blog!

Happy birthday from this side of the planet.

“…each year that passes sees this galaxy more than two extra light years distant from us!”

Does this mean that this galaxy is receding from us at twice the speed of light? If so, then how can we see it?

I guess there was a time that those galaxies weren't moving so fast away, and the light that was emitted in our direction during that pre-faster-than-c-time is what we are observing now.

btw theoretically we could visit those Deep Field clusters in 25 human years, when we are onboard of a spaceship that constantly accelerates with 1G, due to time dilation. But sadly there seems to be that too weird expansion.

"If so, then how can we see it?"

An interesting phenomenon would be, if what I suggested in my previous comment is correct, that there will come a time that clusters start to disappear before our own eyes, zap, zap, zap, …

Happy Birthday Ethan! Hope you blew out all the candles on the cake and wished many more years of writing this wonderfully inspiring blog!

"each year that passes marks an extra million-or-so stars in every galaxy in the Universe."

But the Milky Way galaxy is 13.2 billion years old and only has 300 billion stars (i.e. 3 x 10^11 stars) 1.3 x 10^10 years x 10^6 stars /year = 1.3 x 10^16 stars. I assume there is a reason for this discrepancy.

This is a pretty impressive claim.
So the higher the z (i.e. redshift of a galaxy) the lower the number of stars in the galaxy.
Please point me to a reference.
Or... what am I misunderstanding?

"Even if we launched a spaceship today at 99.999999999%+ the speed of light at this galaxy, it would never reach it. (the farthest galaxy we’ve ever discovered)."

But the highest energy cosmic rays do not travel across the universe at a constant velocity. . they accelerate continuously (somehow) in their journey across the universe. Otherwise, they wouldn't exceed the GZK limit.

Likewise, a spacecraft with low initial velocity that is continuously accelerated by several g's can reach a more distant galaxy than one with an initial (and constant) velocity equal to "99.999999999%+ the speed of light ". As well an initial velocity equal to "99.999999999%+ the speed of light " implies an almost infinite instantaneous acceleration that would kill a human.

Well anyway this is how my spaceship is designed. Still, perhaps I misunderstand something? Let me know.

At any rate, you're still young Ethan. With proper accelleration you still can reach that most distant galaxy before your last birthday. Time dilation due to continuous gravitational accelleration of several g's is the ticket.

So happy birthday, live long as you enjoy and travel the universe.

Happy birthday Ethan. :)

From the pov of a photon, no time passes between the emissionand absorption. Therefore the universe was a set size. From our pov, the universe got bigger and therefore the ohoton got stretched to fit the same number of 'beats' in this longer path.

Thaks to Chelle for explaining Ethan's apparently impossible statement. This shows the value of determining exactly which space-time frame is being considered.

What I missed was that the light by which we see "this galaxy" has been in transit for billions of years and the actual motions of "this galaxy" are not in the same space-time frame as the light or our non-existant perceptions of "this galaxy".

Belatedly, I wish Ethan and everyone else here a Happy Birthday in whatever space-time frame it occurs.

Happy Birthday, Ethan!!!

I know, I missed the date, but, is it yet OK, isn't? ;-)

Jockaira,

Thanks for giving me some credit, but I don't know if my suggestion is correct, because there would be also an other odd thing, and that is the fact that the speed of gravitational waves is the same as the speed of light, so at a certain point Stars would start to be disconnected, because they do not only shines, they also pull .... how is this keeping it all together, are them waves being stretched, like how Wow says that "the photon got stretched"? Perhaps this is something that Ethan could explain in more detail in an extra topic.

You are giving us an excellent thing to read. Keep on with it, I enjoy reading it a lot.... Happy birthday.

Happy Birthday!!! I always enjoy seeing the photos that catch your learned eye.

Happy B'day Ethan.

OKThen, my mistake on the earlier statement on the galaxy's star formation rate. I mis-read a paper a while ago when they talked about a star formation rate as being about an Msun per year as being about a million suns, rather than being about one solar mass per year.

This has been fixed, and check back later today for a new post elaborating on it (with links).

تصاویر بسیار عالی است.واقعا شگفت انگیز و لذت بخشه.
The photoes are very wondeful.thank you

Great post. I came across this while searching for images of the sun from the space station. Surprisingly there are very few, and in the ones I can find the sun appears smaller than I imaged, seeing as its huge. Any thoughts?

Thanks for the post.