A Dark Matter Accretion Disk for Black Hole (Neutron Star)

  • Thread starter PSR1257II
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Hello!

Dark Matter (if exists)(if it is in form of particles - collisionless) could also be attracted by Black Holes (or Neutron Stars) and form accretion disk. I would like to discuss possible properties of such hypothetical object.

DM particles could be trapped and settled in around innermost stable orbit*. But as they are frictionless - they cannot loose energy and traverse down to BH - therefore they should stay on such quasi-infinite orbit(s). On long time span BH can accumulate significant amount of DM, for example with mass ~0.1-1 of mass of BH itself.

For external observer such object would? (question) look like BH with mass of ~1.1-2 of mass of original BH and such characteristics as orbital period of "normal" matter (e,p...) on outer orbits (say, r>=r innermost, 4 rg - gravitational radius) would? (question) be the same as in case of BH with increased mass.

There is other questions like what about drag (if BH is spinning), would it be composition of drag from BH itself and drag caused by DM? What would be value of BH spin J inferred from observation of accretion disk and (independent) measure of mass of such object?

Thank in advance for possible answers.

* The feasibility of settling is probably not high as they are slow ("cold"), for instance escape velocity from Milky Way is ~500 km/sec that makes heavy (say, 1 GeV) particle to be just consumed by BH instead of settling on stable orbit.
 
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Dark Matter ... could also be attracted by Black Holes (or Neutron Stars) and form accretion disk.
No, as I understand it, it could not. DM particles can't be captured into a accretion disk because as you point out, they are friction-less. DM particles either pass close enough to be captured or just keep going by.
 

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