A rotating black hole in the Galactic Center
Abstract
Recent observations of Sgr A* give strong constraints for possible models of the physical nature of Sgr A* and suggest the presence of a massive black~hole with M<2 106 Msun surrounded by an accretion disk which we estimate to radiate at a luminosity of <7 105 Lsun. We therefore calculate the appearance of a standard accretion disk around a Kerr hole in Sgr A* following from general relativity and a few fundamental assumptions. Effective temperature and luminosity of the disk spectra do not depend on the unknown viscosity mechanism but instead are quite sensitive to variations of intrinsic parameters: the mass, the accretion rate, the angular momentum of the accreting hole and the inclination angle. A radiation field of L~7 104 - 7 105 Lsun and Teff ~ 2-4 104 K can be ascribed to a rapidly rotating Kerr~hole (a>0.9) accreting 10-8.5 - 10-7 Msun/yr at a black~hole mass of M=2 106 Msunseen almost edge on. A low mass black hole of M<103 Msun seems to be very unlikely. We provide a ``Hertzsprung-Russell diagram for black holes'' together with simple scaling laws to provide an easy-to-handle test for the black hole model.
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