Dark Matter Mystery Solved?

[hecd2]

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.

Well that BH was found because it's in a binary with a star. I don't expect many of these PBHs are orbiting stars, so even if your estimate for how many there are in our neighbourhood is correct, we wouldn't be able to detect many or any of them. The detection of BHs via production of X-rays from infalling matter is mostly (exclusively?) super-massive BHs. I don't suppose a solar mass or smaller BH minding its business somewhere in the ISM or in the DM halo would be detectable. And in fact the pre-print paper specifically states that X-ray production would have ceased a long time ago.

 

[hecd2]

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.

Alternative theories of gravity include but are not limited to MOND. But few or none of them explain observations across a wide range of situations and scales as well as GR+DM.

 

[RecoveringYuppy]

Well that BH was found because it's in a binary with a star. I don't expect many of these PBHs are orbiting stars, so even if your estimate for how many there are in our neighbourhood is correct, we wouldn't be able to detect many or any of them.

Why would they not be orbiting stars?

The detection of BHs via production of X-rays from infalling matter is mostly (exclusively?) super-massive BHs.

Well, that could also be an indication there aren't many black holes to detect. Note that the object I cited has been viewed in x-rays, it just wasn't detected as a black hole that way.

I don't suppose a solar mass or smaller BH minding its business somewhere in the ISM or in the DM halo would be detectable.

I would think that black holes in the ISM would be occasional x-ray novas but I don't know at what rate they'd be expected to go nova. The one I cited, near a star, has been noticed in x-rays at least twice in the past century(ish).

And in fact the pre-print paper specifically states that X-ray production would have ceased a long time ago.

Didn't see that, haven't read the paper in any meaningful way but did scan for references to x-rays. All the references I saw were speaking of ancient x-ray backgrounds. Why wouldn't black holes in the galaxy be occasional x-ray novas?

, so even if your estimate for how many there are in our neighbourhood is correct, we wouldn't be able to detect many or any of them.

My current estimate has gone up and I've found some supporting information. The density of dark matter in our local region is estimated to be .0088 solar masses per cubic parsec. That translates to 1 solar mass per 113 cubic parsecs. That's a cube with 5 parsec sides. If we're talking 1.44 solar mass black holes or smaller than we should be near a fair number of them. Over a hundred within 50 light years. For comparison, 50 LY is where ~1,000 of the visible stars are.

https://arxiv.org/abs/1408.1787

 

[hecd2]

Why would they not be orbiting stars?

Why would they be? They would have been formed long before the first Pop III stars. I have no way of estimating how many would be in binaries with the current population of stars.

Well, that could also be an indication there aren't many black holes to detect.

Not necessarily - it could mean that we can't detect X-rays from mass gap BHs not in binaries. And indeed why should we?

Note that the object I cited has been viewed in x-rays, it just wasn't detected as a black hole that way.

Do you have a reference for that? I'd be interested to read the paper.

I would think that black holes in the ISM would be occasional x-ray novas but I don't know at what rate they'd be expected to go nova.

Depends on whether they are in binaries.

Didn't see that, haven't read the paper in any meaningful way but did scan for references to x-rays. All the references I saw were speaking of ancient x-ray backgrounds. Why wouldn't black holes in the galaxy be occasional x-ray novas?

Well some might, but only those that are in binaries. So that is an open question for us.

My current estimate has gone up and I've found some supporting information. The density of dark matter in our local region is estimated to be .0088 solar masses per cubic parsec. That translates to 1 solar mass per 113 cubic parsecs. That's a cube with 5 parsec sides. If we're talking 1.44 solar mass black holes or smaller than we should be near a fair number of them. Over a hundred within 50 light years. For comparison, 50 LY is where ~1,000 of the visible stars are.

https://arxiv.org/abs/1408.1787

Well the paper states that the PBHs would be a range of masses from planetary masses to a million solar masses. The latter, I presume, in smaller quantities than the former.

 

[RecoveringYuppy]

Why would they be? They would have been formed long before the first Pop III stars. I have no way of estimating how many would be in binaries with the current population of stars.

They are postulated to have seeded the formation of stars and galaxies. How do they do that without gravitationally interacting? And how do they avoid being captured in to orbits over periods of billions of years with a rate that the numbers seem to show would be over 99%?

Not necessarily - it could mean that we can't detect X-rays from mass gap BHs not in binaries. And indeed why should we?

Because we can detect x-rays? BTW I think these things would lead to events that would produce plenty of visible light also.

Do you have a reference for that? I'd be interested to read the paper.

I came across it in sources cited by Wikipedia:

https://en.wikipedia.org/wiki/A0620-00
https://en.wikipedia.org/wiki/List_of_black_holes

Depends on whether they are in binaries.

Well some might, but only those that are in binaries. So that is an open question for us.

You keep saying "binaries". The kind of x-ray flares that are caused by black holes in binaries are visible across galaxies. We're talking about so many black holes that they would be amongst the nearest stars, possibly even in the outer solar system. You don't need to be consuming a star to be visible across such astronomically short distances.

Well the paper states that the PBHs would be a range of masses from planetary masses to a million solar masses. The latter, I presume, in smaller quantities than the former.

This is getting in to territory that claims there are black holes orbiting the sun (or constantly passing through) that we haven't noticed. Is that plausible? For example, is it possible that whatever is disturbing the Kuiper belt is a black hole that never disturbs something we would that would make that obvious?

 

[rjh01]

<snip>


This is getting in to territory that claims there are black holes orbiting the sun (or constantly passing through) that we haven't noticed. Is that plausible? For example, is it possible that whatever is disturbing the Kuiper belt is a black hole that never disturbs something we would that would make that obvious?

This all depends on the size and location of the black holes. A lot of them may have migrated close to the centre of the galaxy where, if they were drifting on their own they would be hard to detect. There could still be heaps roaming freely around the galaxy and the only way to detect them would be if they came between us and a star. Even if they are orbiting another star they may be hard to detect.

 

[Samson]

This all depends on the size and location of the black holes. A lot of them may have migrated close to the centre of the galaxy where, if they were drifting on their own they would be hard to detect. There could still be heaps roaming freely around the galaxy and the only way to detect them would be if they came between us and a star. Even if they are orbiting another star they may be hard to detect.

They must exist at the perimeter to explain the dark matter "halo".

 

[hecd2]

They are postulated to have seeded the formation of stars and galaxies. How do they do that without gravitationally interacting?

Gravitational interaction at the scale of galaxies and galaxy clusters at z>15 does not equate with the capture of the putative BHs by stars in the current universe.

And how do they avoid being captured in to orbits over periods of billions of years with a rate that the numbers seem to show would be over 99%?

Where does 99% come from? What is the likelhood of capture? I don't know how to compute that.

Because we can detect x-rays? BTW I think these things would lead to events that would produce plenty of visible light also.

By what mechanism other than accretion?

You keep saying "binaries". The kind of x-ray flares that are caused by black holes in binaries are visible across galaxies. We're talking about so many black holes that they would be amongst the nearest stars, possibly even in the outer solar system. You don't need to be consuming a star to be visible across such astronomically short distances.

By what mechanism would a solar mass BH in the ISM not in a binary be visible in the Xray and visible?

This is getting in to territory that claims there are black holes orbiting the sun (or constantly passing through) that we haven't noticed.

I don't see that. The ISM is huge compared to the vicinity of the solar system. Are there stars constantly passing through?

Anyway, I think you make good points in general. The pre-print says nothing about constraints on observation of these PBHs in the local environment, and it's certainly a valid question. I am not as convinced of the answer as you appear to be.

 

[Delvo]

Primordial black holes, of whatever size, would initially be moving in any random direction, at a speed determined randomly within whatever their allowed speed range might be. Gravitational interactions between two objects moving with random velocities rarely result in orbital capture. Usually they just bend each other's paths once and then depart in some new random direction. (Think of ʻOumuamua and our probes' deliberate slingshot maneuvers.) Orbital capture requires a combination of velocities that are aligned & balanced just right, which is unusual in any set of objects whose velocities are random. If that makes you wonder why so many things are in orbit anyway, it's because they usually weren't captured; each set of orbiting things and the thing(s) they orbit usually came from a single original cloud which collapsed into more than one object. The direction of the separate objects' orbits and rotations is the direction of the net asymmetry of particle momentums in the original cloud.

YouTube's best physics channel on primordial black holes overall, and on the possibility that some or all dark matter might be them (both predating this thread's first post's article about the Webb looking for them):

 

[RecoveringYuppy]

This all depends on the size and location of the black holes. A lot of them may have migrated close to the centre of the galaxy where, if they were drifting on their own they would be hard to detect. There could still be heaps roaming freely around the galaxy and the only way to detect them would be if they came between us and a star. Even if they are orbiting another star they may be hard to detect.

Note that I cite a paper that calculates the local density of dark matter. I also did some rough calculations of the density on my own. And, what Samson said, if they are all in the core then that won't match the rotation data we observe.

 

[Gord_in_Toronto]

Here's a view of a bunch of Black Holes. Presumably not the ones making up invisible Dark Matter though.

The Tiny Dots in This Image Aren't Stars or Galaxies. They're Black Holes.

https://www.sciencealert.com/the-ti...-aren-t-stars-or-galaxies-they-re-black-holes

When they're just hanging out not doing much, black holes don't give off any detectable radiation, making them much harder to find. When a black hole is actively accreting material – spooling it in from a disc of dust and gas that circles it much as water circles a drain – the intense forces involved generate radiation across multiple wavelengths that we can detect across the vastness of space.

 

[RecoveringYuppy]

Where does 99% come from? What is the likelhood of capture? I don't know how to compute that.

99% is my rough estimate of how many black holes must be rogue since our planet hunting efforts aren't discovering a bunch of overlooked star mass objects and we don't see many x-ray novas. It's making the assumption that the missing mass is distributed as primarily stellar sized objects.

Basically, I'm thinking that if the mass is primarily stellar mass BHs then they must all be rogue and they must not be producing events that can be seen for a few dozen LY for centuries at a time.

By what mechanism other than accretion?
By what mechanism would a solar mass BH in the ISM not in a binary be visible in the Xray and visible?

Accretion. There is still stuff in the ISM and the outer solar system. And I'm not accepting the idea that a star is the only source of material to interact with.

These numbers imply that black holes must be incredibly close. We don't need an event that is visible for megaparsecs for them to be noticeable. Do black holes have just two modes, nearly perfectly quiet versus events that can be seen across galaxies?

BTW based on a later comment you seem to think I'm convinced of something. I'm not and this point is definitely one of them. Maybe the distribution of matter is such that rogue black holes stay perfectly quiet for centuries. I really just have my own incredulity to go on at the moment. I haven't figured out a way to estimate this well for myself yet and haven't gotten through much of the current paper yet.

I don't see that. The ISM is huge compared to the vicinity of the solar system. Are there stars constantly passing through?

Well, yeah, but it hinges on what you mean by constantly and how close you want. Stars pass within an LY maybe about once every 50K years.

But note your comment mentioned that planetary mass BHs are in the mix.

I think we can rule out that these are dominated by BHs on the large thousand or million mass side, we'd have seen them and the DM we are trying to explain seems to be somewhat uniform. If you run numbers that any significant portion of DM is in the form of planetary masses than the numbers of these things gets very large. For a simple example if you assume it's all in the form of Earth sized black holes then there would be over 100 within a light year. That's where the Solar System comets are. It would be a long time in between pass throughs of the inner solar system though.

So is it possible that we have so many black holes so close and they never do anything we notice? (That's a real question, it's not rhetorical, I don't know the answer).

 

[RecoveringYuppy]

Primordial black holes, of whatever size, would initially be moving in any random direction, at a speed determined randomly within whatever their allowed speed range might be.

Yes, but how much variation?

If that makes you wonder why so many things are in orbit anyway, it's because they usually weren't captured; each set of orbiting things and the thing(s) they orbit usually came from a single original cloud which collapsed into more than one object.

Would the primordial plasma the PBHs collapsed from qualify? That might mean they aren't in orbit about objects that collapsed later but would some of these PBHs be in binary and higher systems with each other? I think that would make them even harder to hide and might even present problems for their life time (gravitational waves).

 

[hecd2]

99% is my rough estimate of how many black holes must be rogue since our planet hunting efforts aren't discovering a bunch of overlooked star mass objects and we don't see many x-ray novas. It's making the assumption that the missing mass is distributed as primarily stellar sized objects.

I don't suppose every stellar mass PBH that was in orbit would be a recurrent Xray source. A-00620-00 is in a very tight orbit with a ~7 hour orbital period. That's close. Close enough to pull the main sequence star into an observably non spherical shape by tidal force. I don't think this orbital condition would be common.

Basically, I'm thinking that if the mass is primarily stellar mass BHs then they must all be rogue and they must not be producing events that can be seen for a few dozen LY for centuries at a time.

Yes.

Accretion. There is still stuff in the ISM and the outer solar system. And I'm not accepting the idea that a star is the only source of material to interact with.

It is far from clear to me that the accretion of matter in the extremely sparse ISM by a stellar mass BH would produce an observable EM signal.

Well, yeah, but it hinges on what you mean by constantly and how close you want. Stars pass within an LY maybe about once every 50K years.

The calculation I saw was 300K years when I googled it, but anyway, I don't see what the relevance is since we have only been looking for a few years. If you want to say that there is a high probability that one of these PBHs is within, say 10ly, fine, but otherwise I'm not sure what the point is. The key question is how much EM radiation does a stellar mass BH in the ISM emit from accretion.

But note your comment mentioned that planetary mass BHs are in the mix.

Yes.

I think we can rule out that these are dominated by BHs on the large thousand or million mass side, we'd have seen them and the DM we are trying to explain seems to be somewhat uniform. If you run numbers that any significant portion of DM is in the form of planetary masses than the numbers of these things gets very large. For a simple example if you assume it's all in the form of Earth sized black holes then there would be over 100 within a light year. That's where the Solar System comets are. It would be a long time in between pass throughs of the inner solar system though.

The authors assume typically ~1 solar mass with a distribution.

So is it possible that we have so many black holes so close and they never do anything we notice? (That's a real question, it's not rhetorical, I don't know the answer).

Neither do I, and it's, as I said before, a valid question, but I don't see any consideration that would make the answer necessarily "no".

 

[hecd2]

OK - so I found this: Gaggero et al, "Searching for Primordial Black Holes in the radio and Xray Sky", 2016: https://arxiv.org/pdf/1612.00457.pdf

They exclude with high confidence that a population of PBHs with masses 10 - 100 solar masses (typically 30 solar masses) can account for the whole DM content of the Milky Way. Their assumed mass distribution is different from the more recent paper though.

 

[HansMustermann]

The idea isn't new. And it's a tempting one.

The main... interest in seeing things explained that I have with this is nebulas. Sure, a black hole passing through empty space won't do much noticeable stuff, but some nebulas can be pretty damn big (and I mean nearly 600 light years big), and dense enough (by cosmic standards) that clumps can collapse into new stars. I mean, our own sun is a third generation star, which means a gigantic first generation exploded into a galaxy-sized nebula, then the second generation stars formed out of that, some exploded into more nebulas, and stars like our sun formed out of that material. So, anyway, I'm thinking, wouldn't such a nebula be a 600 ly sized... well, the equivalent for black holes of what a fog chamber is for particles? We should see SOME X-rays when one passes through a nebula. Plus, wouldn't it cause some distortions to it?

And I'm not just talking stuff at the other end of the galaxy, where we couldn't really tell. There's a 460 ly sized nebula practically in our back yard. I kinda suspect we'd notice if a source of x-rays suddenly started moving through it.

Now mind you, I'm not saying it's flat out wrong. I don't have the qualifications to say so. Plus, I like to keep an open mind in any case. I'd just like to see it explained properly by the people who are qualified.

 

[Delvo]

There's a 460 ly sized nebula practically in our back yard. I kinda suspect we'd notice if a source of x-rays suddenly started moving through it.

Maybe not. Most of our observation gizmos aren't built for X-ray range, and the ones that are might not have been pointed in that direction. But even if they have been, the nebula might not be dense enough to produce X-rays this way, and/or the black holes we're talking about might not be big enough. Remember, even the ones that are big enough to eat a bunch of stars per year go through "active" and "inactive" phases. When there's enough mass around, it glows on the way in, and gets more intense the more there is, with X-ray range being just about the most extreme case. When there isn't, they turn invisible. The one at the middle of our galaxy looks like an empty spot in space at first and was only located by the way it flings stars around. It's in a pretty "inactive" phase, which is about not what it does but about how much mass there is in its area for it to pull in.

 

[RecoveringYuppy]

The one at the middle of our galaxy looks like an empty spot in space at first and was only located by the way it flings stars around. It's in a pretty "inactive" phase, which is about not what it does but about how much mass there is in its area for it to pull in.

I think there is an important distinction that it wasn't located that way. It was located a long time ago by radio emissions. And even in it's inactive phase it's very detectable.

But we're talking worse than apples and oranges here. Grapefruit sized planetary mass PBHs that are very nearby wouldn't have to be x-ray flare stars producing the output of multiple stars to get noticed. To meet the expected density there would be many of them a distances of less than a light year (presuming they are in the planetary mass range). Very roughly, even if it is 1 billionth as bright as a star it would be easily noticeable.

Having said that though, I think the grapefruit size argues in favor of them not encountering much mass. Earth encounters ~100 tons a day of mostly dust. But that is more due to it's size than it's mass. The region that would stress matter enough to heat it up to visible temperatures is very small.