Mini-dark halos with intermediate mass black holes

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  • 28 January 2005
Abstract
Simulations suggest that there are 10^3-10^4 minihalos of 10^6-10^7Msun mass in the Milky Way. We argue that many of these may form central intermediate mass black holes (IMBHs) of mass about 10^3-10^4Msun, which might be naked or enshrouded by gravitationally bound dark matter depending on the kick/recoil velocity at the formation of the IMBH. The IMBH forms by gas accretion on a time-scale longer than the local dynamical time in a minihalo, and hence compresses the surrounding dark matter into a mini-spike of r^-1.5 density even if the hole is formed off-centre in a minihalo with a finite density core. The black hole with mini-spike becomes the centre of the minihalo after dynamical friction. Most of these minihalos survive intact without significant tidal stripping by the Milky Way, and are largely invisible except through point-like annihilation signals (with bolometric luminosities of 10^{3-5}Lsun within 0.01-0.1 pc of their centres) if dark matter is made of neutralinos. Strong limits can therefore be set on unidentified EGRET sources as possible annihilating clumps. The innermost minihalo and its central hole may also orbitally decay into the Milky Way centre, and hence enhance the density of dark matter at the very centre, which could then nurture the growth of the seed IMBH into a supermassive BH.

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