Jonathan C. Tan (Chalmers Univ. & Univ. of Virginia, Gothenburg  & Onsala, SE)

 Formation of Supermassive Black Holes from Population III.1 Seeds

ABSTRACT:   The origin of supermassive black holes (SMBHs) is one of the major unsolved problems of astrophysics. I review different formation theories and then discuss a scenario of formation from supermassive (~10^5 Msun) Population III.1 stars. These are primordial composition first collapse objects unaffected by any external influence from other astrophysical sources, i.e., their formation is only influenced by cosmological initial conditions and the microphysics of baryonic heating and cooling processes. The key process that can allow growth of the stars to ~10^5 Msun mass scales is dark matter annihilation heating, which replaces nuclear fusion as the means of protostellar support. For this mechanism to be effective places constraints on the dark matter particle and also requires colocation of the protostar with the dark matter density peak - a situation which only occurs in Pop III.1 minihalos. Key features of this model are: (1) it naturally explains the minimum mass scale of SMBHs and the dichotomy of these scales from those of normal stellar populations; (2) it is simple, involving just one main parameter, d_iso, i.e., the isolation distance needed from other astrophysical sources for a minihalo to form a Pop III.1 source; (3) and is therefore predictive, i.e., to form all SMBHs by this mechanism requires d_iso of about 100 kpc proper distance, and thus a peak of SMBH seed formation at z~30 and concomitant clustering properties of the sources. Such a value of d_iso is consistent with a simple model of ionization feedback from supermassive star progenitors of SMBHs.