I understand that accretion of normal matter into a super-massive black hole leads to x-ray emissions. Is the same effect expected to occur for dark matter accretion into a supermassive black hole? Are there any good articles (e.g. on arXiv) I could read to learn more about this?
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1$\begingroup$ Normal matter interacts strongly with EM waves (like X-rays) but dark matter does not (assuming dark matter is the usual WIMP). In principle dark matter could emit X-rays, but you'd have to get it a lot hotter than normal matter. $\endgroup$– John RennieJan 19, 2014 at 11:46
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1$\begingroup$ In addition to the John's comments, the dark matter is not going to participate in the mechanics of accretion disk formation in the way that ordinary matter does, and the origin of the x-rays lies in the interaction of the disk with itself and with the magnetic field of the whole. $\endgroup$– dmckee --- ex-moderator kittenJan 19, 2014 at 15:31
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$\begingroup$ @dmckee Why does "the dark matter [...] not [...] participate in the mechanics of accretion disk formation in the way that ordinary matter does"? Won't dark matter be "compressed" when it gets closer to the black hole, and then show similar effects than ordinary matter? $\endgroup$– jochenJan 19, 2014 at 17:01
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$\begingroup$ The accretion disk forms because the infalling dust and gas interacts with itself while still conserving angular momentum about the black hole. Look up Virial heating. The dark matter nearly does not interact, so instead of forming an accretion disk the bits of dark matter just keep orbiting in an unstructured ball. Note that dark matter is not completely non-interacting, so this statement is not absolute. $\endgroup$– dmckee --- ex-moderator kittenJan 19, 2014 at 17:31
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$\begingroup$ Thanks all. If you write your answers as a formal "answer", I can formally "accept" it. $\endgroup$– jochenJan 21, 2014 at 23:17
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Assuming dark matter is a WIMP, NASA made a computer simulation on dark matter particle annihilation to see what would happen when dark matter fell into a black hole. According to the article, it may produce gamma ray as the collisions of dark matter particles increase closer to the black hole.
Here is the preprint for the NASA simulation: http://arxiv.org/abs/1506.06728
And another one: http://arxiv.org/abs/0909.0169
There is, however, some controversy about the validity of these studies. See e.g. this article and this comment and references therein.
