Comments of the Week #50: From hot and dense to co-orbiting rocks

"True happiness comes from the joy of deeds well done, the zest of creating things new." -Antoine de Saint-Exupery

Every week holds an amazing look at the Universe in a unique way here at Starts With A Bang, and this week saw not only a series of new posts from me, but two contributed ones, including the debut of the fabulous Jillian Scudder of Astroquizzical. If you missed anything, here's a look back at what we've covered:

There's been so much that I've had to say, and I'm so thankful for the great things that Jillian and Brian had to say here, too. You've come through as well, with a spectacular slew of statements, questions and answers for all of us. With all that said, let's dive in to your Comments of the Week!

Image credit: RHIC collaboration, Brookhaven, via Image credit: RHIC collaboration, Brookhaven, via

From Wayne King (our original question-asker) on the timeline of the very early Universe: "The list of all the different decays, their sequencing, the re-ionizations, and the timing across adjacent sectors that are cooling at slightly different rates…. just amazing stuff. I’m an accountant/economist by training, and a retired business manager by profession. Cosmology was barely even a word when I went to college back in the 70’s. But its still the topic that I spend hours reading about every day."

The idea that the Universe could be described by our physical laws, the fundamental particles, and simply knowing the initial conditions and extrapolating forwards in time is at the heart of what cosmology is. From ancient times until perhaps the 1960s, cosmology was more of a hypothesis than a full-blown physical theory, as there were too many uncertainties that were simply too large. But with the discovery of the cosmic microwave background, all of that changed.

Image credit: NASA / WMAP science team. Image credit: NASA / WMAP science team.

For the first time, we knew not only the physical laws governing the Universe (General Relativity was well-established, and the Standard Model was very close to complete), but we learned what the initial state-and-conditions of the Universe were to a reasonably high precision. The idea of a "precision cosmology," once a pipe dream, has become a reality thanks to the influx of continually superior data. For the first time, we understand the history of the Universe and almost everything in it with errors and uncertainties on almost everything that are no more than a few percent.

There are still very likely surprises out there, but they are increasingly smaller, subtler and more nuanced surprises. The story I told you here is likely to receive only the most minor of changes -- perhaps including dark matter, perhaps receiving slight QCD alterations -- until the day we die.

From PJ on ice bubbles: "Have to remember that on the next trip to Whistler..."

If you're interested in doing this practically, don't forget the three steps I outlined:

  1. Add glycerine or corn syrup to thicken the bubble walls.
  2. Make sure it's cold enough and that you're in an area that's sufficiently wind-shielded.
  3. Use the technique of soap-bubble-solutioning the desired area before placing the bubble down.

These things are delicate, and take time to form.

But if you do it right, and the conditions are right, your reward is an astoundingly beautiful bauble that's unmatched by anything humans can create. They have a unique -- and transient -- beauty that appears at every stage of the freezing process, from the onset to the very end.

Winter ornament makers, eat your hearts out.

Image credit: NASA / Apollo 12. Image credit: NASA / Apollo 12.

From Ted Lawry on the Moon's crater chains: "If the crater chains are from a tidally disrupted body, would the disrupter be the Earth?"

When you get a comet coming into the inner Solar System, you can be sure of a few things. First, it's going to be moving pretty quickly by time it gets to Earth's orbit, at a bare minimum of 30 km/s (108,000 kph or 67,000 mph) with respect to the Moon. Second, comets are typically mostly icy, porous bodies, and so they're very low density, even the more massive ones. And third, when you get close to any large mass, the tidal forces get larger and larger. We normally think of "spaghettification" as something that happens when you fall into a black hole, but any mass will do. If the Moon can cause the tides here on Earth -- and tidal forces work as a 1/r^3 force -- imagine what they can do to a tenuous comet that's more than 100 times closer to its center-of-mass!

Image credit: Wikimedia Commons user Krishnavedala. Image credit: Wikimedia Commons user Krishnavedala.

A difference -- if you're moving at 30 km/s -- in only one second in impact time means a difference of 30 km on the Moon's surface. Some of these crater chains may correspond to impact time differences of only hundredths of a second, which makes the results easy to understand, if no less spectacular. But to answer you unequivocally, the Moon itself is almost always going to be the disrupting body, and the crater chains are the result of the tidal disruption that we see.

Image credit: me, using the free software Stellarium from Image credit: me, using the free software Stellarium from

From Eric on the night sky after sunset: "I was just thinking about novas and supernovas last night as I walked home. I saw a ‘star’ in the sky so much brighter than the others that I literally stood there for a few seconds wondering if it was going to go boom. I assume it was really Venus (approx. 9pm US East Coast, if anyone wants to enlighten me)."

And Rick answering him: "Venus probably set in the west before 8 PM local time. At 9 PM, Jupiter would be high in the sky toward the east and at magnitude -2, a bit brighter than Sirius which would have been further south."

Not only is Rick correct, he's more correct than he knows. While Jupiter is a bit brighter than Sirius, about twice as bright at this time of year, it's going to appear up to three or four (or more) times brighter, particularly the farther north you are.

Why's that?

Because Sirius appears lower on the horizon, significantly lower, particularly the higher your latitude. The atmosphere causes both a reddening and a dimming effect, and since Sirius has two-to-three times as much of it to pass through as Jupiter at 9 PM this time of year, Jupiter will be far-and-away the brightest (non-Moon) object in the night sky at that time.

As Rick also alludes to, it's still only about one-eighth the brightness of Venus, which unfortunately sets early in the opposite side of the sky.

Image credit: ESO/L. Calçada, artist’s impression, via Image credit: ESO/L. Calçada, artist’s impression, via

From the ever-informative Michael Richmond on Betelgeuse's coming supernova: "Some of the questions about harmful radiation from a nearby supernova can be found at
Short version: Betelgeuse very likely wouldn’t hurt a fly."

That is, to say, not an Earth-based fly. But here's the most relevant part I pulled from his well-written text:

Conclusion: I suspect that a type II explosion must be within a few parsecs of the Earth, certainly less than 10 pc (33 light years), to pose a danger to life on Earth. I suspect that a type Ia explosion, due to the larger amount of high-energy radiation, could be several times farther away. My guess is that the X-ray and gamma-ray radiation are the most important at large distances.

Image credit: NASA, ESA, H. Bond (STScI), and M. Barstow (University of Leicester). Image credit: NASA, ESA, H. Bond (STScI), and M. Barstow (University of Leicester).

Now, there are plenty of white dwarfs that may someday result in a Type Ia supernova explosion that are that close: Sirius B, for example, is a potential "someday" candidate when Sirius A's future white dwarf merges with it, and that will be a Type Ia explosion. However, it will begin receding from us after "only" another 60,000 years, and after a few hundred thousand, won't even be the brightest star in the sky anymore.

But Betelgeuse? It's presently some 500-800 light years away, and will "only" be a type II supernova. So as Michael said, "likely" wouldn't hurt a fly is exactly right.

Image credit: Wikipedia. Image credit: Wikipedia.

From JollyJoker on quantum interpretations: "The Wikipedia table of QM interpretations is interesting. I remember a survey giving Copenhagen as the most popular interpretation among particle physicists but I’d be surprised if so many believed that consciousness causes collapse and reality is non-local."

You must keep in mind two things:

  1. Interpretations are only "preferences" insofar as what people -- even though they may be physicists -- "feel" is right to them. There is no discernible physical difference between any of them.
  2. That "survey" to which you refer was given at a conference to about 33 people.

Copenhagen, by the way, doesn't mean that consciousness causes collapse, but rather that the act of observing collapses a wavefunction/destroys quantum interference's wave-like properties. You don't need to be a conscious observer to be an observer. If a tree falls in the woods and no one's there to see it, the tree knows, the woods knows, and the Universe knows. That seems to be enough.

Image credit: ESO/L. Calçada, of an impression of red dwarf GJ 1214, via Image credit: ESO/L. Calçada, of an impression of red dwarf GJ 1214, via

From Pavel on the death of red dwarfs: "What is supposed to be the temperature of the white dwarf remnants of a red dwarf? As the mass of the red dwarf is slowly mixing and the reaction runs only in core, I suppose it would be only a few thousands degrees – so not too white. Am I right?"

The thing you've got to remember when it comes to stars -- and everything in the Universe -- is that while energy is conserved, temperature is not! Think about the Hertzsprung-Russell diagram, and how a single star evolves.

Image credit: Sloan Digital Sky Survey / SkyServer, via Image credit: Sloan Digital Sky Survey / SkyServer, via

When the Sun becomes a red giant, it becomes redder (cooler) because it not only expands, it expands adiabatically, meaning that its entropy remains constant, and while its volume expands, its pressure changes and its temperature drops. (This happens to the expanding Universe as well.) But when it's totally out of fuel, it adiabatically contracts, and its temperature correspondingly rises, which is why it gets hotter again, and becomes a white (or even a blue) dwarf, rather than a redder color.

Even though M-dwarfs will be red their whole lives, when they die, they will contract adiabatically as well, and hence should increase in temperature. They will -- to the best of my understanding -- become white dwarfs yet!

Image credit: Paul Chodas & Don Yeomans. Image credit: Paul Chodas & Don Yeomans.

And finally from Omega Centauri on our one-and-only trojan asteroid: "Seeing how close the TK7 orbit comes to the orbit of Venus on the map, is it really stable? Or is an interaction with Venus likely to send it flying?"

Don't be fooled by two-dimensional plots of three-dimensional space! While it might look like Venus/2010 TK7 might come very close to one another, is that really true? For one, 2010 TK7 is inclined to the Sun-Earth orbital plane by 19 degrees, so it's almost always way off from Earth (or Venus) interactions.

But for another, 2010 TK7 only ever gets as close to the Sun as 0.81 A.U., while Venus' maximum distance from the Sun is only 0.73 A.U., which means there's a minimum separation of about 0.08 A.U., which is still around 12,000,000 km.

Image credit: Wikimedia Commons user Lookang, with many thanks to author of original simulation = Todd K. Timberlake. Image credit: Wikimedia Commons user Lookang, with many thanks to author of original simulation = Todd K. Timberlake.

So no, it should never get quite close enough to either Venus or Earth to get kicked out of the Solar System, and yet, there it is. The most exciting possibility is that there are still other asteroids/comets captured at L4 and L5, and we simply haven't found them yet.

That's what we know at the moment, and thanks for a great week of comments! See you back here (and at the main Starts With A Bang) for more wonders of the Universe in March!

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I think you misunderstood, when I discussed the potential instability of the TK7 orbit. I was considering whether it could be injected from the Lagrange point, not whether it could be ejected from the solar system. If the distance of the object from Venus is even comparable to its distance from earth, then the forces on the body are at least for a short while not dominated by the sun/earth system, but the forces from Venus is also important. Then there is the possibility that repeated tugs on the object over many encounters might add up.

By Omega Centauri (not verified) on 01 Mar 2015 #permalink