Mini-dark halos with intermediate mass black holes
Abstract
We argue that the Milky Way (MW) contains 10^3-10^4 intermediate mass black holes (IMBHs) of mass 10^{2-3}msun. Some IMBHs are naked, and some are enshrouded by dense dark mini-spikes (with peak neutralino number density 10^8 cm^-3) and by minihalos of 10^6-10^7msun (with mass density above 5 GeV cm^-3). Detectable by GLAST, the mini-spikes and minihalos could dominate the neutralino annihilation in the MW. The IMBH is formed off-centre by gas accretion in a minihalo with a finite density core and compresses the surrounding dark matter (DM) into a mini-spike of r^-1.5 density profile. The mini-spike and IMBH become the centre of the minihalo after dynamical friction. These dense minihalos (the nearest at about 2 kpc) survive mostly without tidal stripping by the MW, and are largely invisible except that their point-like neutralino annihilation signals (with bolometric luminosities of 10^{3-5} Lsun for 50 GeV neutralinos within 0.01-0.1 pc of their centres) stand out well above the MW background and are more luminous than outer dwarf satellite galaxies. Strong limits can therefore be set on unidentified EGRET sources as possible annihilating clumps. If the supermassive BH of the MW orginates from an IMBH, it is also likely enshrouded with a mini-spike.Keywords
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