I Dark matter and black hole interaction

[mfb]

Primordial black holes lighter than a solar mass have been ruled out as large contribution by microlensing searches, black holes significantly more massive have been ruled out by searches for binary systems and other measurements. In the range where the LIGO mergers are, we have an indirect excusion from CMB observations - a bit model-dependent, but a lot of primordial black holes sound unlikely. They could have formed later, however.
Here is a good summary.

 

[DarkMattrHole]

Thanks all for these informed insights on the subject... still remains uneasy on the subject how these DM particles interact along the EH of the DH's and will need much further reading perhaps some new ground going forward.

From the sounds of it, DM particles simply, and silently, follow the laws of gravity, curving through space-time but without the 'friction' of either radiating any energy or by being encumbered by other normal matter particles swept into the outer disk. As i recall, please correct if wrong, DM particles don't interact with other DM particles either, and if so, then being pinned to a BH singularity may be the first and only experience in a DM particles' long life.

 

[Chronos]

PBH's as a significant fraction of the matter budget in the early universe has been virtually ruled out by CMB data. Planck pretty much put the nail in the coffin. This constraint could be avoided if black holes largely originated at later epochs, but, observational evidence suggests this is an increasingly unlikely scenario as new data becomes available.

 

[mfb]

As i recall, please correct if wrong, DM particles don't interact with other DM particles either

They cannot interact too often, but all we can do is set upper bounds. They could interact with each other via the weak interaction. Annihilation is also a possible process.

 

[Buzz Bloom]

My impression was that black holes are almost certainly some of the dark matter.

Hi stephen:

There is a constraint on how much of the matter comprising a BH is DM. To explain this constraint, it is probably useful to designate the fraction of BHs created prior to the primordial nuclear synthesis (PNS) of helium and deuterium occurred as Primoridial BHs (PBHs), and use "BH" for later formed BHs. Note that PNS started within the first few seconds following the big-bang.

The constraint is that the density of deuterium observed to exist in the universe depends on the density of baryonic matter (BM) during PNS, which in turn constrains the ratio of BM to DM that exists today. As explained in this thread, most (almost all?) of the content of a BH is BM. Therefore it is not reasonable to consider BHs to comprise any significant amount of DM. On the other hand, it is not known how much of the pre-PNS matter consisted of PBHs, and it is not known how much of PBHs consisted of DM, since the mechanism for forming PBHs is not known. This means it is possible that much of the matter in PBHs may have been and still may be DM, but this is entirely speculative.

Regards,
Buzz

 

[maria_phys]

Assuming that our central black hole is sucking dark matter, can we explain the reason why it's mass is 10^9 solar masses? Dark matter interacts with the ordinary matter (or with any stellar object) via gravity, thus the mass of a black hole is increasing without having any paradox (at first sight).

 

[mfb]

Black holes do not "suck". They attract things based on their mass like everything else does. The amount of dark matter falling into the central black hole (or any other black hole) is tiny.

 

[maria_phys]

Black holes do not "suck". They attract things based on their mass like everything else does. The amount of dark matter falling into the central black hole (or any other black hole) is tiny.

Why? I imagine exactly the opposite. Dark matter interacts with the ordinary matter only via gravity. Assuming an object with very strong gravity, the dark matter would fall immediately into the black hole because of this strong interaction. So, all the dark matter of the universe would fall into the primordial black holes. Hmm, that seems not correct..

Something I'm missing...

Thank you for your answer, anyway :)

 

[phinds]

Why? I imagine exactly the opposite. Dark matter interacts with the ordinary matter only via gravity. Assuming an object with very strong gravity, the dark matter would fall immediately into the black hole because of this strong interaction. So, all the dark matter of the universe would fall into the primordial black holes. Hmm, that seems not correct..

Something I'm missing...

Thank you for your answer, anyway :)

See post #2 --- it explains what you are "missing"

 

[Drakkith]

Why? I imagine exactly the opposite. Dark matter interacts with the ordinary matter only via gravity. Assuming an object with very strong gravity, the dark matter would fall immediately into the black hole because of this strong interaction. So, all the dark matter of the universe would fall into the primordial black holes. Hmm, that seems not correct..

In order to fall into a black hole your path would need to take you directly into the event horizon. But black holes are usually very tine. A black hole of perhaps a few solar masses is only about a dozen miles in diameter or something. The chances of any dark matter crossing that tiny section of space is minuscule.

Note that gravity isn't like a vacuum cleaner. Objects don't spiral into a black hole unless they have some way to slow down so that they "fall" towards the black hole. For regular matter, collisions in the accretion disk slow the dust and gas and, over time, lead to a slow in-spiral until it passes the event horizon. Since dark matter doesn't interact with itself or with normal matter though anything but gravity, it cannot collide with anything and thus cannot lose speed and fall into the event horizon.

 

[phinds]

In order to fall into a black hole your path would need to take you directly into the event horizon. But black holes are usually very tine. A black hole of perhaps a few solar masses is only about a dozen miles in diameter or something. The chances of any dark matter crossing that tiny section of space is minuscule.

Note that gravity isn't like a vacuum cleaner. Objects don't spiral into a black hole unless they have some way to slow down so that they "fall" towards the black hole. For regular matter, collisions in the accretion disk slow the dust and gas and, over time, lead to a slow in-spiral until it passes the event horizon. Since dark matter doesn't interact with itself or with normal matter though anything but gravity, it cannot collide with anything and thus cannot lose speed and fall into the event horizon.

As I said; see post #2