Mini-dark halos with intermediate mass black holes

Abstract

We argue that the Milky Way (MW) contains thousands intermediate mass black holes (IMBHs) and minihalos with a fraction of IMBHs still being enshrouded in extremely dense mini-spikes of dark matter (DM) particles. Each containing $10^6\msun$ of dark particles and no baryons in a sphere of 50 pc radius, the minihalos are dense enough to survive the Milky Way tide with the nearest minihalo within 2 kpc from the Sun. The IMBH is formed off-centre in a minihalo by gas accretion, and its growth adiabatically compresses a finite density of surrounding dark matter into a $r^{-1.5}$ mini-spike. Some IMBHs recentre on their minihalos after dynamical friction, and some IMBHs are ejected by birth kicks. Detectable by GLAST, the mini-spikes and minihalos should stand out the background and dominate the neutralino annihilation in the smooth MW and satellite galaxies. If they are the unidentified EGRET sources, upper limits can be set on the branching ratio of neutralino annihilation. The supermassive BH of the MW, if orginates from an IMBH, is also likely enshrouded with a mini-spike.