[HN Gopher] Supermassive Dark Star candidates seen by JWST
___________________________________________________________________
Supermassive Dark Star candidates seen by JWST
Author : misja111
Score : 194 points
Date : 2023-07-14 13:04 UTC (9 hours ago)
(HTM) web link (www.pnas.org)
(TXT) w3m dump (www.pnas.org)
| andsoitis wrote:
| > 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 wrote:
| > 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 wrote:
| 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.
| orra wrote:
| > If the DM particles are their own antiparticles, then
| their annihilation provides a heat source
|
| How much if this is speculation? Also, do other particles
| behave like this?
|
| I didn't realise particles could be their own
| antiparticles, but it transpires that e.g. photons are,
| because all photons are neutral, not charged somehow.
|
| However, even though a proton is its own antiparticles, two
| photons do not annihilate, right?
| ben_w wrote:
| > Also, do other particles behave like this?
|
| Yes, as you note, photons are their own antiparticles.
|
| The maths doesn't have a preferred time direction, so two
| photons can annihilate into an electron-positron pair.
|
| I'm not sure if this has actually been observed given how
| hard it is. That said, my favourite type of supernova is
| caused by pair creation, though I don't know the
| proportion of that which comes from 2-photon
| interactions: https://en.wikipedia.org/wiki/Pair-
| instability_supernova
|
| There's also Majorna particles, but as I understand it
| the only known particles that are definitely Majornas are
| also quasiparticles:
|
| https://en.wikipedia.org/wiki/Majorana_fermion
| kamilner wrote:
| Notably it does bound the energy of gamma rays over long
| distances (as the higher the energy the more likely it
| will annihilate with other photons along the way.)
|
| The wikipedia article on the Breit-Wheeler process has
| some history of the work on experimental observations,
| although I don't know how accurate or up to date it is
| https://en.wikipedia.org/wiki/Breit-Wheeler_process
| AnimalMuppet wrote:
| > The maths doesn't have a preferred time direction, so
| two photons can annihilate into an electron-positron
| pair.
|
| But only if their energy is high enough. So by that
| reckoning, photons below 511 keV don't have
| antiparticles, and those above it do. That's pretty
| weird. So maybe it's better to say that photons aren't
| really their own antiparticle, but they might
| theoretically destroy each other in some rare
| circumstances.
| [deleted]
| gus_massa wrote:
| > _Also, do other particles behave like this?_
|
| Nobody is sure, but some people think that neutrinos are
| they own antiparticle
| https://en.wikipedia.org/wiki/Neutrino#Majorana_mass I
| never liked that theory, but some people that know more
| than me about particle physics liked it.
|
| There were some experiment using atoms that decay
| ejecting two neutrinos, and hopping that in some case the
| two neutrinos will annihilate each other. https://en.wiki
| pedia.org/wiki/Neutrinoless_double_beta_decay . IIRC,
| none of the experiments found the strange annihilation,
| so perhaps neutrinos are not their own antiparticle :) .
| jessriedel wrote:
| 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.
| floxy wrote:
| >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
| Quinner wrote:
| 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-scratch wrote:
| 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.
| CyanBird wrote:
| Baryonic matter is not symmetrical with its antiparticles.
| I forget the percentage given that it is not my subfield,
| but it was very high, meaning the existing amount of matter
| is just a sliver of what was initially "created"/coagulated
|
| https://en.m.wikipedia.org/wiki/Baryon_asymmetry
| nonameiguess wrote:
| As far as models model, most of the regular matter did
| annihilate. If I'm remembering correctly, the fact that
| anything we can see and feel still exists is an asymmetry
| between matter and antimatter somewhere in the arena of
| 30,001 particles for every 30,000 antiparticles. Obviously,
| very nearly all of this annihilated, and all of the matter
| that still exists is the residue of this early asymmetry. I
| don't exactly keep up to date on this stuff, but this
| either was or still is one of the bigger open questions
| regarding the Big Bang. What caused this asymmetry? It was
| one of the classic examples of apparent fine tuning.
|
| As for why dark antimatter/matter pairs would persist
| longer rather than run out (I guess that's the opposite of
| what you're saying, but it's important to remember what
| we're seeing even looking back this far is way after the
| normal matter/antimatter annihilated immediately after
| inflation), it's effectively the same reason dark matter
| doesn't clump and retains it's roughly spherical form at
| larger than entire visible galaxy sizes. Regular matter
| interacts via the electromagnetic force, which has an
| infinite interaction radius. Charged particles repel and
| attract each other from large distances. Thus, fundamental
| particles don't need to get that close to each other to
| form atoms and molecules. Dark matter only interacts via
| the weak force, which has a tiny interaction radius. The
| fundamental particles need to more or less make a direct
| beeline to the same point in spacetime to ever touch each
| other, which has an extremely low probability of ever
| happening. It's the same reason Earth can be bombarded
| nonstop with unimaginably large numbers of neutrinos every
| second from the sun, yet virtually all of them go straight
| through everything. All of space is mostly empty space,
| even things that look solid to us because the wavelengths
| we can discriminate are much larger than the spaces between
| atoms and molecules. It wouldn't look that way to dark
| matter. It would look actually empty.
| denton-scratch wrote:
| > Dark matter only interacts via the weak force, which
| has a tiny interaction radius.
|
| And gravity, or so I'm told.
|
| But both gravity and the weak force are fields, and so
| just like EM, they pervade space. Isn't that right? The
| weak force weakend dramatically with distance, but it
| doesn't disappear - I thought one property of a field is
| that it pervades spacetime.
|
| Not that that makes any difference to your argument.
| mtlmtlmtlmtl wrote:
| They are both fields, but gravity is different in that
| spacetime itself _is_ the field.
|
| As for the weak force, I think that's not necessarily a
| known property of DM, but rather a property of
| hypothetical candidates for being the dark matter known
| as WIMPs(weakly interacting massive particles).
| jeremyjh wrote:
| Anti-matter is very rare with normal matter, so we don't
| see it running out. But if dark matter and dark anti-matter
| are both just as common then you could see it play out as
| they suggest.
| denton-scratch wrote:
| But then there wouldn't be any dark matter, and we
| wouldn't be arguing about halos.
| pfdietz wrote:
| Some models of dark matter have the particles being their
| own antiparticles.
| pantulis wrote:
| If that was the case, given the abundance of DM, wouldn't
| we be detecting lots of energy due to their own
| annihilation?
| JumpCrisscross wrote:
| Is it just charge that causes particles to have an
| antiparticle?
| pfdietz wrote:
| No. Neutrons and antineutrons are different particles,
| for example.
| lanna wrote:
| Neutrons don't have charge, but their quarks do.
| Antineutrons have quarks with reversed charge.
|
| Just like a neutral atom can have a neutral antiatom.
| addaon wrote:
| If you prefer, then, neutrinos are neutral but have an
| anti-particle (although it's still possible that
| neutrinos are Majorana particles, in which case they're
| their own anti-particle).
| bowsamic wrote:
| > 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.
| idiotsecant wrote:
| [flagged]
| bowsamic wrote:
| I'm not sure why what I said warranted such an aggressive
| response. Can you explain more?
| MattPalmer1086 wrote:
| I did not read the parent post as aggressive at all. Maybe
| you could chill out a bit?
| sebzim4500 wrote:
| For what it's worth your comment reads about ten times more
| obnoxious than the guy you are replying to.
| wyager wrote:
| 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.
| some_furry wrote:
| There's also the Unruh effect, where being in a gravity
| well causes radiation
| https://en.wikipedia.org/wiki/Unruh_effect
|
| (I don't know if this is relevant at all! Just an
| interesting tangent)
| andsoitis wrote:
| 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.
| Sharlin wrote:
| As the article says, the proposed mechanism is self-
| annihilation, which would presumably produce energy in the
| form of perfectly ordinary photons.
| AnimalMuppet wrote:
| That seems wrong. "Dark matter" usually means matter that
| doesn't interact with photons, not just "matter that is
| dark because no light is shining on it". But if it emits
| photons, even in a matter-antimatter reaction, then it
| couples with photons, and so it can't be dark matter in
| that sense.
| simonh wrote:
| Sure, it's only called dark matter because we find it
| hard to observe it.
| Sharlin wrote:
| Apparently (eg. [1]) there would be a couple of different
| pathways available for WIMP annihilation, to a W+W- boson
| pair, or to m+m- muon pair, or a e+e- electron-positron
| pair, so the immediate annihilation products would be
| charged non-dark matter particles which would either
| quickly decay or annihilate into photons or simply shed
| their energy via normal EM interactions.
|
| [1] P. Salati, 2014. Dark Matter Annihilation in the
| Universe. https://arxiv.org/abs/1403.4495
| Beldin wrote:
| 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.
| bowsamic wrote:
| > If it could heat up, Dark Matter wouldn't be dark.
|
| I don't think this is correct at all. A system doesn't have
| to interact with EM to be thermodynamic. If you can define
| a temperature for it and there is the possibility for
| energy transfer, then it can heat up
| ninkendo wrote:
| > there is the possibility for energy transfer
|
| I think this is where the debate is. I'm not a physicist
| but my understanding of the current dark matter models is
| that it doesn't interact with itself in a way that could
| be thought of as "energy transfer" (ie. like particles
| that collide), but only gravitationally. This would mean
| there's no real way for a dark matter "particle" to
| transfer momentum to another particle, and thus no real
| way for "heat" to exist as such.
| bowsamic wrote:
| Gravity can transfer energy. For example gravitational
| waves transfer energy. They can be used to boil a kettle
| of strong enough
| gnatman wrote:
| [flagged]
| Pxtl wrote:
| 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?
| Sharlin wrote:
| 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_...
| Pxtl wrote:
| 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?
| gjhan wrote:
| In the context of this paper, the DSs are significantly
| smaller than galaxies, but JWST doesn't have enough
| resolution to distinguish a galaxy from the much smaller
| DS.
|
| In their DS model, what seems to limit the rate at which
| the DM annihilates is that any interaction between DS
| particles has a low probability of happening (a cross
| section). We can imagine this as particles just whizzing
| around each other, gravitationally bound (i.e. confined to
| a nearby volume) but so small that they have a low
| probability of actually interacting.
| Sharlin wrote:
| Not _that_ diffuse; the objects in question are so far away
| that they 're not resolved by JWST. They look like point
| sources, no matter whether galaxy-sized or vastly smaller
| (the hypothetical DS objects would "only" be solar-system
| sized). DM self-annihilation would be rare enough (both due
| to low DM density and tiny reaction cross-section) that it
| wouldn't burn out very quickly. The heat (and thus
| pressure) generated by the annihilation would indeed keep
| the DSs from collapsing into "real" stars.
| djkorchi wrote:
| Is there actually a balance needed between pressure and
| collapse? Radiation pressure presumably doesn't do
| anything to the constituent dm particles. Similarly,
| wouldn't the particles in the star be on various
| elliptical trajectories and not collapse?
| marcosdumay wrote:
| > Similarly, wouldn't the particles in the star be on
| various elliptical trajectories and not collapse?
|
| That's a common misunderstanding. Orbits around many
| bodies do not work that way, and the particles exchanging
| momentum so they collide or escape the cloud is normal.
| Sharlin wrote:
| The DM particles would indeed be on random/chaotic
| orbits, unlike visible matter which can shed kinetic
| energy via EM interaction (collisions). But DM density
| near a mass concentration would still be higher than far
| away from anything massive.
|
| Normal stars are in hydrostatic equilibrium, a density
| where the inward force exerted by gravity and the outward
| force exerted by the pressure of the hot plasma are
| balanced. In a dark star the situation would be similar,
| except the heat would be generated by DM annihilation
| rather than fusion (the heat from annihilation would keep
| the star too "puffy" to reach the core pressure and
| temperature required for fusion.
| CydeWeys wrote:
| You're forgetting about friction. A diffuse cloud is
| eventually going to become tighter and tighter as gravity
| draws it together and the individual orbiting particles
| within that cloud lose momentum from hitting each other.
| Pxtl wrote:
| Well, they say the DS would also have a decent amount of
| baryonic matter in it - some diffuse hydrogen and helium.
| If the pressure from the annihilations pushes the
| hydrogen and helium outwards, that could create some
| outward gravity to pull on the dark matter, right? Wait,
| except the outward gravitational pull inside of a hollow
| shell is zero because it all cancels.
|
| Would there even be friction though? It sounds like the
| only interactions these hypothetical particles have is
| gravity and annihilation.
| Sharlin wrote:
| Yes, no friction for the DM particles. WIMP DM cannot
| collapse by shedding kinetic energy as heat like visible
| matter can. Thus the dark matter halos around galaxies.
| But gravity would still cause there to be a higher
| average density of DM inside and near the dark star (or
| indeed a modern-day galaxy) than far away from any
| massive objects.
| floxy wrote:
| >Yes, no friction for the DM particles
|
| Chandrasekhar dynamical friction?
|
| https://en.wikipedia.org/wiki/Dynamical_friction
| CydeWeys wrote:
| > If the pressure from the annihilations pushes the
| hydrogen and helium outwards, that could create some
| outward gravity to pull on the dark matter, right?
|
| But it's not on net being pushed outwards. It's in
| equilibrium. The outward push is on average exactly
| canceled out by the baryonic matter falling inwards due
| to friction. If it weren't, then everything would get
| either denser/sparser until equilibrium were regained.
| The point is that the forces are working in such a way as
| to maintain a stable equilibrium, like in normal stars.
| [deleted]
| nonameiguess wrote:
| 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.
| phkahler wrote:
| >> 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...
| mr_mitm wrote:
| > 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?
| phkahler wrote:
| >> As if there was a giant conspiracy by Big Cosmology.
| What makes you think asking questions isn't welcome?
|
| Because they're not? Proposing a specific distribution of
| fairy dust immediately begs two questions. "What is it?" -
| ok I'll let that slide, but "why that distribution?" is
| critical. It is claimed to influence regular mater via
| gravity, so why should it take on a different distribution?
| It "solves" one problem but creates many more. Hey if
| there's a math model to explain one phenomenon, why does it
| differ from the existing stuff under the same influence? If
| peer review doesn't force them to address such questions,
| there is no hope for me to do so.
| sebzim4500 wrote:
| There is no shortage of explantions aimed at a smart
| highschool or undergraduate student which will answer
| most of those questions. Obviously not "what is it?",
| that is one of the biggest open questions in cosmology.
| jeremyjh wrote:
| The answer is you have to understand the math to
| understand the theory. Popular accounts are always an
| approximation, but if the theory were easily refuted by
| lay people, scientists would not be basing entire
| research programs on it.
| cvoss wrote:
| The inevitable process of science involves raising
| questions that, at first, do not have answers.
| Publications are not exam papers where peer reviewers
| have the answer key. The process of science is also a
| communal activity, where one scientist raises a question
| in one forum, and the answer comes from a different
| scientist years later. Peer review should not and does
| not (per your own admission) suppress the raising of
| unanswered questions. And this contradicts your earlier
| claim that asking questions isn't welcome.
| roywiggins wrote:
| 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.
| cvoss wrote:
| 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
| AnimalMuppet wrote:
| 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?
| dylan604 wrote:
| 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).
| roywiggins wrote:
| This paper predicts that dark stars would have a distinct
| spectrum that would distinguish them from ordinary galaxies.
| nwallin wrote:
| > 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.
| [deleted]
| phkahler wrote:
| The word they should be using is hypothesis, not theory. A
| theory stands up to scrutiny.
| mr_mitm wrote:
| That's not how the term "theory" is used in science. Only
| hobbyists care about the distinction, actual scientists
| infer the implied certainty from context. There is Born's
| rule, Noether's theorem, Newton's law (which we know is
| wrong), Einstein's theory of GR, the standard model (which
| is the best thing we have), ... sometimes we use the word
| "a quantum theory" to mean a certain Lagrangian, even one
| which we know does not describe reality at all.
| consilient wrote:
| > Noether's theorem
|
| is not like the other entries on your list. It's a full-
| blown mathematically rigorous theorem (that incidentally
| also happens to be of central importance in physics), not
| a physical model.
| dylan604 wrote:
| there you go, an even better word. good thing i don't call
| myself a scientist
| sesm wrote:
| 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.
| fhars wrote:
| I sort of like the idea of a "dark star" shining "with up to ten
| billion solar luminosities"...
| bongwater_OS wrote:
| They didn't need to use JWST to find a transcendental Dark Star,
| they could have just looked at Fillmore West in 1969.
| ajross wrote:
| 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 wrote:
| There are two possible mechanisms referred to in the article:
| weakly interacting particles (WIMPs) or self-annihilating dark
| matter.
| [deleted]
| jbotz wrote:
| 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.
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