Dark matter annihilation in the gravitational field of a black hole

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In this paper we consider dark matter particle annihilation in the gravitational field of black holes.

• We obtain exact distribution function of the infalling dark matter particles, and compute the resulting flux and spectra of gamma rays coming from the objects.
• It is shown that the dark matter density significantly increases near a black hole.
• Particle collision energy becomes very high affecting relative cross-sections of various annihilation channels.