Comments of the Week #70: From the ultimate darkness to variable stars

“It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn’t feel like a giant. I felt very, very small.” -Neil Armstrong

This past week saw a whole lot of interesting things happen, including tonight's second full moon of the month: a rare blue moon. In my life, I saw the International Space Station for the first time, but here at Starts With A Bang, there was so much to learn about and share, including:

There was also a fun piece about our Solar System's two-toned moon over at Forbes:

In addition, we reached our second milestone goal on our Patreon, so if you want to vote on which book chapter everyone gets for free in advance of my first book's release, join and donate today. Other than that, it's on to our Comments of the Week!

Image credit: White Dwarf, Earth, and Black Dwarf, via BBC / GCSE (L) and SunflowerCosmos (R). Image credit: White Dwarf, Earth, and Black Dwarf, via BBC / GCSE (L) and SunflowerCosmos (R).

From Omega Centauri on neutron stars going dark: "Sounds like the low temperature neutrino emissions rate is not well known. How else could there be such a large variation in estimated cooling time?
Can neutrinos really pass through neutron stars, even with a tinyl cross-section the column density of a NS is phenomenally high."

There are two question here, both worthy of an answer and both contrary to what Omega Centauri expects. You see, when you first form a neutron star, you're taking the core of a massive star that's so big that the core itself -- the part that becomes the neutron star -- is more massive than our entire Sun. It collapses down and fuses into a ball of neutrons just a few kilometers wide, heating up to tremendous temperatures of about 10^12 K at the core and 10^6 K at the surface.

Image credit: ESO/L. Calçada, via Image credit: ESO/L. Calçada, via

It's actually not the low-temperature cooling that's a problem; we understand how neutrons behave at low temperatures. It's not even the high-temperature cooling, although that's less well understood. (We spend a lot less time with neutrons at 10^12 K than we do at lower temperatures.) It's the high-density decay time and its gradient, since even though the binding energy is great enough that neutrons shouldn't decay, they will on long enough timescales thanks to quantum tunneling. Without a perfect model of neutron star interiors, we recognize that the uncertainties in computation leave an uncertainty there. Additionally, your neutrons are more likely to decay close to the neutron-star crust, where the binding energies are lower. Even though the uncertainty is small overall, the decay times are so long that this leads to a few order of magnitude uncertainty in the cooling time of a neutron star.

But don't worry about your neutrinos interacting. Sure, neutron stars are incredibly dense: about 10 times denser than a Uranium nucleus on average. But they're also small, at just a few kilometers in radius. So the overall "chances-to-interact-with-a-particle" are only a few times as great your chances for an interaction if you emit a neutrino from the center of the Sun, and most of them are close to the surface anyway. If you randomly pass that neutrino through the core, you've got a few percent chance of an interaction (which is high!), but that's a relatively unlikely path. Most neutrinos escape just fine.

Image credit: © 2015 Brian Kane, via Image credit: © 2015 Brian Kane, via

From PJ on advertising vs. art: "Then the thought of safety struck home. All these distractions along the highways & byways. Imagine, not knowing the signage was there, in the evening (night) there is an apparition of a phase of the moon before the driver – the moment of panic – WTF – simply because it should not be there.
Once the driver gets used to the sight, however, the brain tends to block such things; unless there is a constant change – a slide show, or something of that nature.
Don’t get me wrong, progress has its place; I would rather see a tree, though, than a picture of one."

I don't know, honestly, how well it works, but I always feel like the biggest weirdo when I'm driving down a dark road at night. If the Moon is out, or the stars, or bright planets, I'll try and sneak a peak every chance I get at the sights of the natural beauty out beyond our Earthly skies.

Yes, I know it's dangerous, driving at some 70 mph (110-120 kph) or so, looking at anything other than what's directly in front of (and around) you. But that's the whole point of advertising: to distract you from what you're doing and occupy that mental space with the craving to get you thinking about the product, service or cause in question. For me, if my options are between:

  • actual nature,
  • simulated nature,
  • nothing at all, or
  • an advertisement,

those are my choices, in my order of preference. Only actually restoring the natural setting would be a superior choice, to me, from what this art project accomplished.

Image credit: Multiwavelength images of M31, via the Planck mission team; ESA / NASA. Image credit: Multiwavelength images of M31, via the Planck mission team; ESA / NASA.

From Jan on the topic of where I publish: "But have you considered publishing on anything else but medium? It really is not good. Those images are 90 degrees rotated. Logical top and bottom of the “composite” image are one bellow another. They are split into many pieces, one can’t even save them and view them properly. RSS does not work there and more."

At the very least, I know that RSS does work on Medium: my blog's feed is here.

Writing about the Universe -- actually, teaching about it and sharing its wonders and joys in general -- is what I'm passionate about. Where and how I do it isn't of the most paramount importance, but enjoying it, giving my audience a good experience and making (as close to) a living as I can doing it are what I value. That latter reason is something I can't do on my own (but I'm trying with the Patreon), but right now, Medium is the best of all those worlds for me.

Perhaps down the road, though, it won't be. Have any input on what might be next?

Image credit: Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF. Image credit: Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF.

From G, on the "big" question about "small" things like us: "In 1/2 billion years, the Sun will boil Earth’s oceans, so by that time our distant descendants will need to have spread into an interstellar civilization, or Earth-originated life will be another tragic footnote in a distant civilization’s galactic history logs. As we spread across the galaxy, we will discover numerous forms of life in other star systems, and reached some viable conclusions about the types of life that are possible in our galaxy.
But that will not answer the question of whether biology is convergent across galaxies. The only way to get that answer is to go to another galaxy."

And then there's the next logical question, if you want to go down that rabbit hole: even though, as far as we can tell, the physical processes of our own galaxy are at play in all galaxies, does that mean the way "life" is realized is the same in our galaxy or local group is the same everywhere? Do giant ellipticals in the heart of Virgo have the same life processes, or are there others unique to its environment?

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

Do isolated, field galaxies have different types of life that arise? How about more processed material, like that found at the heart of the Perseus cluster (above)?

What we've already learned about the Universe is amazing; what we continue to learn is amazing as well. But there will always be more to learn and check out there, and right now, the only thing limiting our knowledge is the resources we're willing to invest.

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

From Scott on dark matter halos: "I thought the rationale behind dark matter halo theory was that the inner and outer portions of a rotating galaxy have the same red shift, or velocity relative to the observer."

That's only one piece of evidence for dark matter halos. If you add a non-collisional component of matter to the Universe, you get large, fluffy, diffuse halos around all massive structures, which actually act as seeds for the massive structures in the first place.

But observationally, there was a piece of evidence that came first (like, 40 years before the rotation curves of galaxies were measured): galaxy clusters and the speeds of the individual galaxies in them. In fact, when we reconstruct what the mass profile of a galaxy cluster looks like, we find that sure, individual galaxies have large masses, but there's an even greater amount of mass distributed in a diffuse, cluster-scale halo!

Image credit: Greg Kochanski, Ian Dell'Antonio, and Tony Tyson (Bell Labs), of the reconstructed mass in a large galaxy cluster. Image credit: Greg Kochanski, Ian Dell'Antonio, and Tony Tyson (Bell Labs), of the reconstructed mass in a large galaxy cluster.

This is to say there's a lot more evidence for dark matter halo theory than just the rotation curves of galaxies. They play a part, but that's actually the least strong evidence out there.

Image credit: NASA/ESA/Richard Massey (California Institute of Technology). Image credit: NASA/ESA/Richard Massey (California Institute of Technology).

From Boris Borcic on a possibility for dark matter: "Long shot, but on dark matter not possibly being formed of neutrinos, I’d like to be shown that a Fermi gas of (slightly massive) neutrinos can’t achieve dark matter density."

The problem with neutrinos isn't that they couldn't achieve the necessary density of dark matter: if each type of neutrino had a mass of about 4 eV, we'd be golden. (They're constrained, experimentally, to be less than about 2 eV apiece, by the way.) The problem is that if neutrinos made up this dark matter, that dark matter would be hot, which means it would be moving relatively quickly when neutral atoms were formed. It would suppress the formation of structure on large scales, something that vehemently disagrees with observations.

Image credit: Maroto A.L., Ramirez J., astro-ph/0409280. Image credit: Maroto A.L., Ramirez J., astro-ph/0409280.

It's the clustering data that rules this scenario out. Based on the measured mass of neutrinos and the constraints we have, neutrinos appear to be about 0.4% of the dark matter, a number that could increase to a maximum of about 2%, but not more.

It's a good idea, but one that was explored in incredible detail... and ruled out.

Image credit: Aurore Simonnet, Sonoma State University. Image credit: Aurore Simonnet, Sonoma State University.

From Jim Salsman on primordial black holes as dark matter: "[I]f inflation resulted in sufficient intermediate mass black holes (around 100,000 solar masses each) to explain the formation of relatively recently [discovered] quasars at z>6, those would require that all dark matter be comprised of such black holes, and they would not be detectable through gravitational lensing."

This statement is phrased as a "this is true," but in reality it should be asked as, "is this true?" If you allow for the fluctuations inflation produces normally (Gaussian), this is impossible. Producing a fluctuation of more than about 10^-4 solar masses would be ruled out convincingly by power spectrum and CMB data; that can't happen. So you need an exotic scenario -- something involving topological defects -- to produce fluctuations at specifically one scale preferential to all others, and that won't mess up any of our other observations. It is very, very difficult to do this.

Image credit: Sebastian F. Bramberger, Robert H. Brandenberger, Paul Jreidini, and Jerome Quintin, via Image credit: Sebastian F. Bramberger, Robert H. Brandenberger, Paul Jreidini, and Jerome Quintin, via

But the kicker is this: you don't need to! Gaussian fluctuations -- the kind inflation normally predicts -- can give you the supermassive black holes needed all the way up to a redshift of 15-20 or so through the process of hierarchical mergers. At the redshift of z=6 that you referred to, in fact, in the graph from the only one of the three papers that mentions the scenario you put forth, they show how Gaussian fluctuations lead to SMBHs of ~10^9 solar masses with no problem, beginning from that tiny 10^-4 seed. So what you contend is a plausible (but fringe) explanation, but one that's not required to explain what we observe. The standard picture does just fine.

But if we start seeing these objects at, say, a redshift of 30, then we've got a reason to listen.

Image credit: X-ray: NASA/CXC/U.Birmingham/M.Burke et al. Image credit: X-ray: NASA/CXC/U.Birmingham/M.Burke et al.

From Denier on the pieces of evidence for dark matter: "There are implications on all of the above listed phenomena currently attributed to Dark Matter if it is confirmed that antimatter falls up."

If antimatter falls up, we would be tremendously surprised. A lot of things would be wrong. E=mc^2 would be wrong, for one, or gravitational and inertial mass would not be identical. We're doing the experiment because we have to check all our theories and expectations against the evidence, but we have been attempting to measure this for maybe 50+ years now, and haven't been able to create and track neutral antimatter precisely enough to check it out. We will keep trying, and hopefully we'll verify that it falls in a gravitational field just like we expect.

We see antimatter ejecting out of galactic "jets" with the same velocity profiles as we see for normal matter, so we do expect it to behave gravitationally just like matter does. But we don't know for certain until we check. Still, if it turned out that antimatter falls up, I would say it'd be the biggest surprise and discovery of the 21st century. I'll keep watching.

Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-Hubble/Europe Collaboration; Acknowledgment: H. Bond (STScI and Penn State University). Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-Hubble/Europe Collaboration; Acknowledgment: H. Bond (STScI and Penn State University).

And finally, from Wow on the different types of variable stars: "Well, as far as I’m aware, there are three types of variable.

Inherently variable. Stars that change their luminosity.

Multistar variables. Objects that change their luminosity because they appear to be a singe object when they are not.

Occulted variables. Stars that have their brightness changed by having something dark move in front of them."

This is one way to categorize them, but I was only referring to the inherently variable ones. Even within the inherent variable category, there are a whole slew of different types:

Image credit: NASA, ESA, H.E. Bond (STScI) and The Hubble Heritage Team (STScI/AURA). Image credit: NASA, ESA, H.E. Bond (STScI) and The Hubble Heritage Team (STScI/AURA).
  • Pulsating variable stars, including Cepheids, RR Lyrae, long-period variables, Mira variables, slow irregular variables and more. This was the major type that I wrote about, but there are others.
  • Eruptive variable stars, which shed large amount of mass over long timescales. These include Proto-stars, Herbig Ae/Be (pre-main-sequence) stars, giants, supergiants and hypergiants, luminous blue variables, Wolf-Rayet stars and others.
  • And explosive/cataclysmic variable stars, including novae, recurrent novae, dwarf novae and supernovae, among others.

The most important thing I wanted people to take away is that the stars are not fixed, even inherently, but evolve both inside and at the surface, and that every star will have a period in its life where it inherently varies in its brightness, often in the extreme.

Thanks for a great week, and I'll see you back next week for even more!


More like this

Ethan, I would have put those three all in the inherently variable type.

Yes, they're all three different methods of varying, but they have different reasons for being, one being "it's the star", and there are multiple reasons for that, as you said. Another being "Only because we're not able to separate the stars out". The last being "there's dark stuff obscuring it"

I suppose a fourth would be "It's an optical illusion" such as microlensing and the like.

I put them in three mostly because what science you learn from each is dependent on different areas of science to work out what event is producing the variation. The first one stellar evolution the second optics and the third geometry.

Intrinsic variation is the case with all stars, however. Heck, it HAS to, merely because all of them require the balance of energy production and gravity when they operate at different time scales, hence *necessarily* must go out of balance and then have the balance returned (to overshoot again and then recover from that...cyclically).

But there are many different ways for intrinsic variation to occur, whereas the other two are much simpler (if you can afford to ignore or have already removed the effects of other variations). You can just decompose the others.

I don't know I'd put catastrophic variables in there, though, except for accretion binaries and (darn, can't remember the name now, something like "aggressive" or "rough" or "violent" could it be "burster"?) other types of catastrophe that still leaves the situation capable of repeating it many many times.

I mean, there's variation in the stages of red giant from He burning to Fe burning cores, but they don't really repeat. Or not for long anyway.

That's really just personal preference, though.

As to Jim's post, I discarded the post not because the paper was rubbish but that it didn't really support the claims about it "solving" the problem of DM.

Added to that the asinine claim "It's the ONLY answer to the high-z AGN!!!!" that's really showing someone who is too in love with a theory to be a safe graduate scientist.

AN answer? Fine. An elegant and solid answer? Well, OK. "THE ONLY ANSWER!" HELLS NO.

Professors get well into their pet theories. Often their theories are solid, often otherwise.

But their students can often be so "star struck" that they really go "full retard" with overselling the theory merely because their prof preferred it.

And that's what I believe Jim was doing wrong.

Mind you, I've never thought the theory much cop. Hell, AGNs may be the result of coalescing black holes, which is very likely the method you get such honking big ones in galactic centres. Certainly the virulent ones we see today in enough detail appear to be a long aftermath of supermassive black holes merging in the past.

Hell, the higher energy density always seemed potentially enough to explain larger than "normal" (in today's cold universe) black hole production. Though I never knew whether I'd stopped my working out at the point I got the answer I wanted or whether it really stopped there. Certainly there's reason enough to believe the higher energy density would create smaller or even repress black hole production.

It just felt more satisfactory if a hot universe produced bigger stars that made larger black holes. Don't know why.

I like the comment about anti-matter and the Einstein theorem being wrong. I think that the ideology of Issac Newton is long over due for challenge. For some unknown reason Newtonian ideas are considered untouchable or basic science inherently true. Why i have no idea, when Newton was formulating his clockwork ideology clocks were the cutting edge of technology and at the time other ideologies were put forward - much more complex than the simplistic Newtonian so discarded. It must be realized that the myth of objectivity and logic in science must be discarded, No one is objective and few logical unless you take Sherlock Holmes as logical when the fictional character states that men are more intelligent than women because (logically) men's brains are heavier and bigger. No one is objective? Well a totally objective human is one who has total control over their mind - have a perfect mind with perfect thoughts- have total control over their emotions-never become angry or depressed, passionate or need sex or fall in love.

By Vic Newman (not verified) on 03 Aug 2015 #permalink

"For some unknown reason Newtonian ideas are considered untouchable or basic science inherently true"

I can tell you the reason: it's a shibboleth of your own mind. It isn't real. Your claims are false. Not true. Bollocks. Made up. Fiction.

General Relativity changed Newtonian Gravity. Kills your "thesis" dead.

Quantum Mechanics threw out your clockwork areas of Newton's laws. Kills your "thesis" dead.

"It must be realized that the myth of objectivity and logic in science must be discarded,"


"No one is objective and few logical "

The scientific method guards against objective and your claim here is illogical.

"have a perfect mind with perfect thoughts- have total control over their emotions-never become angry or depressed, passionate or need sex or fall in love."


For a start a claim based on fuck all.

Second, most people don't need sex.

And love, like all other emotions are an inherent part of the brain and cannot be removed from it.


I won't go into your idea that Newtonian ideas are irrationally defended; Wow did a good job of refuting that idea. However, you do seem to have a bit of difficulty with confusing individual scientists with the scientific endeavor taken as a whole. No doubt, individual scientists can be illogical, irrational and biased. However, a scientific idea that results from a lack of logical reasoning or from a lack of objectivity must still stand up to the scrutiny of the rest of the scientific community.

Scientists are (or should be) professional skeptics. Faced with a new idea (even their own) the first thing a scientists should do is try to prove it wrong. If it is their own idea, then the scientist should put forth his/her best effort to prove it wrong, and failing to do so, publish that idea so the rest of the scientific community can have at it. If the rest of the community cannot find anything wrong with the idea, it starts to gain acceptance as a valid finding.

Obviously, scientists are human, so this process does not always work perfectly. However, there seems to be no better way to reliably gain knowledge about the universe than this process. The illogical and non-objective thinking that humans are prone to tends, over time, to be overcome by this process, and evidence tends to be the deciding factor. That's the reason why it seemed that Newton's ideas were entrenched; the evidence supports them. In fact, the evidence, at least in the realm of "everyday" scales still supports Newtonian physics. (Everyday taken to mean bodies larger than molecules moving at speeds that are not an appreciable fraction of the speed of light). Only when scientists began pushing the boundaries of Newtonian physics down to very small particles or to bodies moving near the speed of light did the evidence show that Newton's ideas are not the full story.

The moral of this all is if you find fault with current scientific understanding, you don't have to just sit there and argue with all the hard-headed scientists who won't listen to you. Do something about it. Formulate your ideas precisely. Figure out all the reasons that these ideas might not be right. Figure out ways to test your idea. If it passes all the tests you can think of, publish your results showing your tests and explaining your idea clearly so others can consider it and perform their own tests of it. Of course, that's pretty tough; it's much easier to just complain that scientists think they know it all and won't listen to anyone else's ideas.

Nice to meet you
My name is "Satou Hiroshi". It is a Japanese novelist living in Japan.
As I want to use the photograph of the following URL with my novel, please admit it.

Image credit: Greg Kochanski, Ian Dell' Antonio, and Tony Tyson (Bell Labs), of the reconstructed mass in a large galaxy cluster.…

I pray.

By Satou Hiroshi (not verified) on 28 Feb 2017 #permalink