Dark Matter Mystery Solved?

[Gord_in_Toronto]

Dark Matter mystery solved? And the answer is . . . Ta Da . . . Black Holes!

We may finally be able to test one of Stephen Hawking's most far-out ideas

https://www.livescience.com/testable-primordial-black-holes-theory

In the 1970s, Hawking proposed that dark matter, the invisible substance that makes up most matter in the cosmos, may be made of black holes formed in the earliest moments of the Big Bang.

Now, three astronomers have developed a theory that explains not only the existence of dark matter, but also the appearance of the largest black holes in the universe.

OK. So maybe soon then.

 

[Puppycow]

Very cool. I mean, the idea that black holes might explain dark matter has occurred to me too, but in the past it never seemed to be one of the leading candidates for dark matter among physicists.

A simple solution
In the latest research, Natarajan, Nico Cappelluti at the University of Miami and Günther Hasinger at the European Space Agency took a deep dive into the theory of primordial black holes, exploring how they might explain the dark matter and possibly resolve other cosmological challenges.

To pass current observational tests, primordial black holes have to be within a certain mass range. In the new work, the researchers assumed that the primordial black holes had a mass of around 1.4 times the mass of the sun. They constructed a model of the universe that replaced all the dark matter with these fairly light black holes, and then they looked for observational clues that could validate (or rule out) the model.

The team found that primordial black holes could play a major role in the universe by seeding the first stars, the first galaxies and the first supermassive black holes (SMBHs). Observations indicate that stars, galaxies and SMBHs appear very quickly in cosmological history, perhaps too quickly to be accounted for by the processes of formation and growth that we observe in the present-day universe.

"Primordial black holes, if they do exist, could well be the seeds from which all supermassive black holes form, including the one at the center of the Milky Way," Natarajan said.

And the theory is simple and doesn't require a zoo of new particles to explain dark matter.

"Our study shows that without introducing new particles or new physics, we can solve mysteries of modern cosmology from the nature of dark matter itself to the origin of supermassive black holes," Cappelluti said in the statement.

So far this idea is only a model, but it's one that could be tested relatively soon. The James Webb Space Telescope, which launched Christmas Day after years of delays, is specifically designed to answer questions about the origins of stars and galaxies. And the next generation of gravitational wave detectors, especially the Laser Interferometer Space Antenna (LISA), is poised to reveal much more about black holes, including primordial ones if they exist.

So, Occam's Razor likes a solution that doesn't require new physics or new particles to explain the observations.

My dad thinks that neutrinos are dark matter, fwiw.

 

[hecd2]

I find this a very exciting idea because it seems to kill several birds with one stone and does so in a very parsimonious manner. Moreover, it will be subject to observational testing in the relatively near future - the coincidence of the paper with JWST is remarkable. Very exciting.

The preprint is available here: https://arxiv.org/pdf/2109.08701.pdf

I am puzzled about one thing. The popular article linked above talks about the PBHs being all of a single size near the Chandresekar limit. That popular article links to another popular article on the Yale website which says the same thing. However, the paper itself states clearly that a monochromatic mass function for the PBHs is ruled out by observation, and their model uses a wide distribution of PBH mass, from planetary mass to a million solar masses. In their model the PBHs form at four separate events when particles freeze out of the quark-gluon plasma (W and Z bosons; baryons; pions; and electron/positron annihilation with increasing PBH mass at each event).

So it seems that Paul Sutter, who is a professor of asrophysics, didn't read the paper when writing his piece, but relied on the erroneous information on the Yale website. Or I am misunderstanding something.

 

[RecoveringYuppy]

And the theory is simple and doesn't require a zoo of new particles to explain dark matter.

So these PBHs are expected to be the complete explanation for dark matter? That implies the Milky Way is 85-95% black holes that we haven't noticed. At the 1.4 Solar Mass size that has been ciited (not clear to me that applies now) that would mean they outnumbers stars about 5 to 1.

 

[hecd2]

So these PBHs are expected to be the complete explanation for dark matter? .

Yes.

 

[Thermal]

Shouldn't we have been able to detect this superabundance of localized matter if this theory was the case? Like light bending at outrageous distances from these theorized holes, many times beyond our current models?

Eta: I'm certainly no even dilettante physicist, but my understanding is that the only reason we even theorize these massive amounts of undetectable matter and energy is because the math stopped working if we didn't assume it? I always thought if your math was producing nonsense results, that was a tip that you were on entirely the wrong track. Kind of like Ptolemy's epicycles.

 

[Thermal]

So, Occam's Razor likes a solution that doesn't require new physics or new particles to explain the observations.

Does it like the assumption that the universe is comprised of like 95% matter and energy that is unobserved and undetectable? Sounds a little like new physics and/or new particles.

 

[hecd2]

Shouldn't we have been able to detect this superabundance of localized matter if this theory was the case? Like light bending at outrageous distances from these theorized holes, many times beyond our current models?

No, these would be relatively modest masses, mostly not more than a few solar masses.

Eta: I'm certainly no even dilettante physicist, but my understanding is that the only reason we even theorize these massive amounts of undetectable matter and energy is because the math stopped working if we didn't assume it?

I don’t think so. We infer the existence of dark matter and dark energy because observations indicate them. Sure, you can hypothesise alternative theories of gravity for example, but none suggested so far successfully fit all the data which is best fitted by GR plus dark energy and dark matter.

 

[hecd2]

Does it like the assumption that the universe is comprised of like 95% matter and energy that is unobserved and undetectable? Sounds a little like new physics and/or new particles.

If the suggestion in the paper under discussion proves correct then it explains the existence of DM without any new particles beyond the standard model.

 

[Darat]

Shouldn't we have been able to detect this superabundance of localized matter if this theory was the case? Like light bending at outrageous distances from these theorized holes, many times beyond our current models?

Eta: I'm certainly no even dilettante physicist, but my understanding is that the only reason we even theorize these massive amounts of undetectable matter and energy is because the math stopped working if we didn't assume it? I always thought if your math was producing nonsense results, that was a tip that you were on entirely the wrong track. Kind of like Ptolemy's epicycles.

Yes and no.

Often the maths proceeds the evidence if you like - best current example is gravity waves first proposed by Poincaré at the start of the 20th century, predicted by Einstein a few years later but only directly observed almost a hundred years later in 2015.

We know there are gaps in our understanding, some big gaps that seem to need to be stuffed with a "here be dragons" sorry dark energy. As far as I've understood it this idea is telling us what that "here be dragons" is rather than undermining the best models we have.

 

[Thermal]

No, these would be relatively modest masses, mostly not more than a few solar masses.

Isn't this supposed to account for that missing 75% of matter in the universe?

I don’t think so. We infer the existence of dark matter and dark energy because observations indicate them. Sure, you can hypothesise alternative theories of gravity for example, but none suggested so far successfully fit all the data which is best fitted by GR plus dark energy and dark matter.

Again, my somewhat hung-over lay person understanding is that they are not indicated, per se. They are just gratuitously shoved in because nothing works if you don't just say it's all there.

 

[Thermal]

If the suggestion in the paper under discussion proves correct then it explains the existence of DM without any new particles beyond the standard model.

But it would seem to indicate new physics, at the least. Also a monstrous volume of undetectable matter that doesn't reflect or absorb light kind of sounds a little different than the properties of particles we know about.

 

[Thermal]

Yes and no.

Often the maths proceeds the evidence if you like - best current example is gravity waves first proposed by Poincaré at the start of the 20th century, predicted by Einstein a few years later but only directly observed almost a hundred years later in 2015.

We know there are gaps in our understanding, some big gaps that seem to need to be stuffed with a "here be dragons" sorry dark energy. As far as I've understood it this idea is telling us what that "here be dragons" is rather than undermining the best models we have.

Yeah, I get that you can't trash all of your models because they start to fail, if you have no valid competing model. Maybe it's just semantic. Rather than looking for Dark Matter, it should be framed as looking for the phenomenon that gives the illusion of needing Dark Matter to make things work out.

 

[hecd2]

Isn't this supposed to account for that missing 75% of matter in the universe?

Yes, there would be a lot of them.

Again, my somewhat hung-over lay person understanding is that they are not indicated, per se. They are just gratuitously shoved in because nothing works if you don't just say it's all there.

Trolling?

 

[theprestige]

No, these would be relatively modest masses, mostly not more than a few solar masses.

In which case there would have to be A LOT of them. If Thermal's estimate of 5:1 PBH to stars in the Milky Way, shouldn't we be seeing them eclipse visible stars literally all the time?

 

[hecd2]

But it would seem to indicate new physics, at the least.

Well new physics is needed anyway as we cannot explain observations without either dark matter (of whatever constitution) or a different theory of gravity.

Also a monstrous volume of undetectable matter that doesn't reflect or absorb light kind of sounds a little different than the properties of particles we know about.

Not if the matter is in black holes.



What is your objective here?

 

[RecoveringYuppy]

In which case there would have to be A LOT of them. If Thermal's estimate of 5:1 PBH to stars in the Milky Way, shouldn't we be seeing them eclipse visible stars literally all the time?

That was my estimate and I suspect, after further reading, that most of them would be in what is called the "dark matter halo" of the galaxy which turns out to be much larger than I had recalled. I haven't had a chance to figure out the expected density in our immediate region of space.

 

[hecd2]

In which case there would have to be A LOT of them. If Thermal's estimate of 5:1 PBH to stars in the Milky Way, shouldn't we be seeing them eclipse visible stars literally all the time?

Yes, there would be a lot of them. But they are small - the Schwarzschild radius of a stellar mass BH is about a kilometer - a planetary mass BH is of the order of meters. And they'd be mostly much much further from stars than planets are. We only routinely see planets eclipse stars because they are very close to the star in interstellar terms.

 

[RecoveringYuppy]

For reference, here is a link to a small black hole relatively close to Earth. It can't be seen visually (or at least it wasn't detected that way) but was detected by it's gravitational affects. It's 1,500 LY from Earth.

https://news.osu.edu/black-hole-is-closest-to-earth-among-the-smallest-ever-discovered/

Not sure how many stars we've had a chance to examine for these kinds of gravitational affects. Also not sure how many places there are for a black hole to be invisible and not producing x-rays due to infalling matter.

My really rough estimates so far are suggesting there would have to be about 50 closer black holes that we haven't found yet for this to be plausible.

 

[Delvo]

Shouldn't we have been able to detect this superabundance of localized matter if this theory was the case?

No, the dark-matter-is-black-holes hypothesis involves much smaller black holes. You can make a black hole the size of a grape, if it's only got as much mass as the earth.

my understanding is that the only reason we even theorize these massive amounts of undetectable matter and energy is because the math stopped working if we didn't assume it? I always thought if your math was producing nonsense results, that was a tip that you were on entirely the wrong track. Kind of like Ptolemy's epicycles.

It doesn't stop working or produce nonsense. It works perfectly within our solar system and within binary star systems. The problems only came up at galactic scales. (Stars at the outside area of a galaxy seem to be orbiting as if the galaxy were more massive than the stars in it.) That's not the math not working or producing nonsense; it's the math needing some adjustment with scale at worst. And, along with dark matter, such adjustments have also been proposed. They're called "MOND" theories (modification of Newtonian dynamics). But MOND has its own problems, the biggest being formations like the Bullet Cluster where the center of gravity isn't even in the same place as the center of visible mass.