Dark matter annihilation in the vicinity of a black hole.

We consider dark matter annihilation in the gravitational field of a black hole. 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. We also discuss possible experimental consequences of these effects. [ABSTRACT FROM AUTHOR]