Supermassive Dark Star candidates seen by JWST

https://www.pnas.org/doi/10.1073/pnas.2305762120

by misja111 • 3 years ago

218 82 3 years ago

andsoitis2• 3 years ago

The first phase of stellar evolution in the history of the universe may be Dark Stars (DS), powered by dark matter (DM) heating rather than by nuclear fusion.

Is "heating" the right way to think about the power from dark matter? Isn't "heating" a function of regular energy and matter?

misja111• 3 years ago

Dark Stars, which are made almost entirely of hydrogen and helium with less than 0.1% of the mass in the form of DM.

So most of the dark star is still ordinary matter, DM just adds a bit of extra gravity.

holmium• 3 years ago

But, it's the DM that would provide the heat/glow for the star:

If the DM particles are their own antiparticles, then their annihilation provides a heat source that stops the collapse of the clouds and in fact produces a different type of star, a Dark Star, in thermal and hydrostatic equilibrium.
Three key ingredients are required for the formation of DSs:
1) sufficient DM density
2) DM annihilation products become trapped inside the star
3) the DM heating rate beats the cooling rate of the collapsing cloud.

jessriedel3• 3 years ago

Heat is an abstract thermodynamic concept that does not depend on the particle species. For instance, the leading class of theory of dark matter is called "cold dark matter", and this literally refers to the temperature of the dark matter.

floxy3• 3 years ago

The different theories on dark matter (cold, warm, hot) refer not to the temperatures of the matter itself, but the size of the particles themselves with respect to the size of a protogalaxy

https://phys.org/news/2016-08-dark-matterhot.html

bowsamic3• 3 years ago

Isn't "heating" a function of regular energy and matter?

I'm a bit confused at what made you think this. If there is any way to transfer energy from it to something else (which there must be, else it would be impossible to ever interact with it), then it can heat in exactly the same way as anything else.

andsoitis2• 3 years ago

Thanks. That makes sense.

I think the confusing thing for me is that dark matter doesn’t interact with the electromagnetic field so it doesn’t reflect, absorb, or emit electromagnetic radiation.

But your explanation makes sense to me.

wyager• 3 years ago

Conceivably there could be interactions which are sufficiently constrained to prevent the equipartition theorem from coming into play in practice. For example, an interaction with a massive carrier may not be able to support thermal transfer except at very high energies.

Gravitational heat transfer would, I assume, work for everything, but it would also be very very slow.

We're a little bit spoiled by EM - it makes thermal interactions happen quickly and at all energy scales.

Beldin• 3 years ago

Not OP, but:

If there is any way to transfer energy, then it can heat in exactly the same way as anything else.

If it could heat up, Dark Matter wouldn't be dark. So yeah, dark matter that heats isn't quite what one would expect.

Quinner• 3 years ago

The authors are supposing that dark matter at this stage of the universe has its own particles and antiparticles and they are annihilating each other, the energy released by that annihilation is generating the heat.

denton-scratch3• 3 years ago

Thanks, I wondered where this notion of "DM heating" came from, and why the DM "ran out".

But if the DM runs out, then you'd expect the same to happen for non-DM matter, which it doesn't.

Pxtl3• 3 years ago

I'm surprised to read an article with so much assumed knowledge about dark matter - about how it heats, etc. Is there a good place to read about the current best-guesses of the properties of dark matter?

dylan6042• 3 years ago

Isn't the concept of dark matter just an assumption in itself? Seems to follow that any knowledge about it would be an assumption. In fact, that seems like good science, on instead of the word assumption, one might use theory. Once the theory is built up to test, it might actually one day become fact (or proven wrong).

phkahler3• 3 years ago

The word they should be using is hypothesis, not theory. A theory stands up to scrutiny.

roywiggins2• 3 years ago

This paper predicts that dark stars would have a distinct spectrum that would distinguish them from ordinary galaxies.

nwallin• 3 years ago

Isn't the concept of dark matter just an assumption in itself?

Dark matter is not an assumption. Dark matter is not a hypothesis. Dark matter is not a theory.

Dark matter is a series of observations of the universe. Galaxies spin are observed to spin differently than our models and estimates of their mass say they should. Velocities of galaxies in galaxy clusters are much faster than the sum total of the gravitational effects of the cluster can account for. The bullet cluster lenses gravity in a distribution that is not in accordance with the matter that we see. The CMB (cosmic microwave background) is lumpy, too lumpy for our models. This is dark matter; dark matter is a series of observations where the stuff we see does not line up with what our models predict. Dark matter is not an assumption. Dark matter is opening our eyes and looking at the sky.

Now, we can have different theories of dark matter. Hypotheses or theories that attempt to explain the observations. Currently the leading theory is WIMPS, but MACHO and MOND were in the running for a while.

By way of analogy, we have known that light was a thing for thousands of years. Light is not an assumption. Light is not a hypothesis. Light is not a theory. Light is the observation that we are able to see. Light is the observation that we see better when the Sun is up than when a full Moon is up, and sometimes barely at all if there's a new moon or if we're in a cave. Light is the observation that the Sun is brighter than the Moon. Light is the observation that we can make a fire, perhaps a campfire, or a candle, or a torch, that can enable us to see in the dark. Light is the observation that if we put the fire out, we can't see anymore. There were several theories that tried to explain what light is; the Greek theory about our eyes sending out feelers, or waves in the luminiferous aether, or a stream of billiard ball-like particles, or waves in the electromagnetic field. We can have a meaningful discussion about which of these theories is the best one, but we can't have a meaningful discussion about whether the phenomena known as "light" is an assumption: We can see. Therefore light, whatever it happens to be, does exist.

Dark matter is no different.

phkahler3• 3 years ago

> I'm surprised to read an article with so much assumed knowledge about dark matter - about how it heats, etc.

Exactly! I'm astounded at the amount of - quite literally - made up unsubstantiated assumptions about DM. My favorite is to "explain" a galaxy rotation curve by assuming a spherical distribution of DM around the galaxy, but never explaining why or how it would take on such a distribution. Just don't ask questions...

roywiggins2• 3 years ago

The paper is trying to explain some unexpected observations by the JWST. It starts with the idea that maybe these observations are dark stars, works backwards to show that there are a couple of models of dark matter where this would work, and then predicts that, if these really are dark stars, they'll have a measurably different spectrum than regular stars. Measuring the spectrum would then substantiate (or not) a model of dark matter. This sort of thing is how they might nail down a more likely model of dark matter.

This is not unlike trying to explain those observations with ordinary matter, working backwards to try and work out what distribution of ordinary matter could produce the observations and what sort of physics would create such a distribution.

mr_mitm2• 3 years ago

Just don't ask questions...

The insinuation packed in this statement is beyond ridiculous. As if there was a giant conspiracy by Big Cosmology. What makes you think asking questions isn't welcome? Go visit your local college, they probably have a weekly seminar open for everybody. Observe how they interact. Scientists and students ask each other questions (and I mean hard questions) all the time. Pointing out failures in each other theories is the scientists' favorite past time. It's literally how science works.

The structure formation of dark matter is extensively studied and simulations are in good agreement with observations (not perfect though, look up the dwarf galaxy problem).

I'm astounded at the amount of - quite literally - made up unsubstantiated assumptions about DM.

This is done all the time in cosmology: let's assume X is true just for the heck of it, what does that mean for Y? Could we observe it? Would it perhaps explain several observations at once?

Even toy worlds or toy models are explored all the time, by which I mean worlds or models that we know do not describe our world. Valuable insights can still be gained.

And why wouldn't they make some assumptions? Would you prefer it if certain ideas are forbidden to be explored?

cvoss2• 3 years ago

You're are implicitly assuming something that cosmologists do not assume: that DM even exists. It is not assumed to exist. It is proposed to exist as an explanation for observations we have made. As such, the proposing scientists are free to set the terms of their own proposal.

The whole reason DM was proposed is because, if true, it explains gravitational phenomena of galaxies that we can observe but can't otherwise explain under the current best theory of gravity. (Some alternative proposals include very different theories of gravity, rather than DM. [0])

The weakly-interacting property of the proposed DM (again, this property is not an assumption; it's part of the proposal) is what leads to the spherical distribution. It is a (very well explained) mathematical consequence of the lack of interaction that the DM retains a spherical distribution while the ordinary matter collapses to a plane.

[0] https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics

AnimalMuppet3• 3 years ago

But if the dark matter gravitationally affects the visible matter in the galaxy, then the visible matter in the galaxy should gravitationally affect the dark matter. So even if there was reason for the dark matter to initially assume that shape, what's keeping it in that shape against the pull of the visible matter?

Sharlin6• 3 years ago

So-called cold dark matter [1] is the currently favored hypothesis. The Dark Star hypothesis additionally assumes that the CDM particles interact with each other even though they do not interact with baryonic ("normal") matter (other than via gravity). If they do, they'd be their own antiparticles and would annihilate on collisions. This process would produce the energy, in the form of ordinary photons, that powers the Dark Stars.

Like all proper scientific hypotheses, the DS hypothesis makes testable predictions, and now it appears that some relevant JWST observations support, or at least do not conflict with, the DS hypothesis. At the same time, the more mainstream model of protogalaxies and Population III stars [2] has some difficulties explaining the same observations. Of course, this is only very slight evidence in favor of the DS model, but that's science for you. Small steps.

[1] https://en.wikipedia.org/wiki/Cold_dark_matter

[2] https://en.wikipedia.org/wiki/Stellar_population#Population_...

Pxtl3• 3 years ago

So wait, the hypothesis is that the reason Dark Stars are so diffuse that they look like galaxies is that maybe dark matter self-annihilates, so it can't coalesce into true stars? But what keeps it from just all annihilating quickly? Can't ever reach the critical mass of gravity needed for rapid annihilation because it's destroyed as fast as it accumulates? The annihilation provides repulsive force keeping them from collapsing too fast? Or is there no repulsive force?

nonameiguess2• 3 years ago

This is the Proceedings of the National Academies of Science. It's getting shared here, but the target audience is other physicists, who would have this background knowledge.

sesm• 3 years ago

Basically, there are 2 hypothesis: WIMPs and MACHOs.

WIMPs stands for Weakly Interacting Massive Particles, and proposes that DM consist of yet unknown massive particles that don’t interact much with regular matter. The problem with that hypothesis is that no such particles are predicted by Standard Model and decades of searching for any traces of those particles didn’t yield anything.

MACHOs stands for Massive Compact Halo Objects and assumes that DM in galactic halos consists of some known dark objects, most likely Black Holes. The question is: where those black holes come from. There is a model of cyclical universe by Gorkavyi, Mathers et al, where those are primordial black holes left from the previous cycles of the universe. It also explains galaxy formation in early universe (observed by JWST) and predicted gravitational wave background recently discovered by NANOGrav.

ajross• 3 years ago

Seems like a reasonably professional paper by real authors, but the abstract seems suspiciously handwavy while the content is a bit thick for me. Can we get a BS check from the physicists here? Is this a good area for inquiry or just mining a giant data set for confirmation of a wonky idea?

Also: what's the "heating" mechanism proposed? Dark matter infall would pick up energy I guess, but if it's expected to interact only with gravity that doesn't seem likely to do anything meaningful vs. the same cloud contracting on its own? What's being heated?

samus• 3 years ago

There are two possible mechanisms referred to in the article: weakly interacting particles (WIMPs) or self-annihilating dark matter.

fhars• 3 years ago

I sort of like the idea of a "dark star" shining "with up to ten billion solar luminosities"...

bongwater_OS• 3 years ago

They didn't need to use JWST to find a transcendental Dark Star, they could have just looked at Fillmore West in 1969.

jbotz• 3 years ago

So, IIUC, this is an alternative to the paper that was discussed a couple of days ago saying the Universe might be twice as old as previously thought. The "problem observations" both of them try to address are what appear to be huge galaxies at an early time (according to redshift) when there shouldn't have been such large galaxies yet. The aforementioned paper says maybe the Universe is actually much older. This paper says maybe those huge early galaxies aren't actually galaxies but "Dark Stars" instead.

neuralengine• 3 years ago

Not attempting to claim malfeasance or anything but PNAS has a weird "contributed article" track (this article is one of them) in which the authors _can pick their own reviewers_ [1].

"Only 18% of direct submissions were published in 2013, whereas more than 98% of contributed papers were published, according to figures on the journal's website" [2].

[1] https://www.pnas.org/author-center/member-contributed-submis...

[2] https://www.nature.com/articles/510330a

Supermassive Dark Star candidates seen by JWST

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