Dark matter dynamics in Galactic center

Abstract

The evolution of dark matter in central areas of galaxies is considered (the Milky Way is taken as an example). It is driven by scattering off of dark matter particles by bulge stars, their absorption by the supermassive black hole and self-annihilation. This process is described by diffusion equation in the phase space of energy and angular momentum. The equation was integrated for several different models of initial dark matter distribution and using various assumptions about the dynamical factors. It turns out that because the Milky Way center is rather dynamically old (~5 relaxation times t_r), the difference in initial conditions almost vanishes. The density attains a nearly universal profile, and the gamma-ray flux from dark matter annihilation lies in rather narrow range, which enables more robust determination of the dark matter parameters. By present time the mass of dark matter inside the black hole sphere of influence (r<2 pc) has been reduced approximately twice, mostly because of heating by stars. It is shown that the dynamics of dark matter for t>t_r is determined mainly by stars outside the sphere of influence.