Astronomy and Astrophysics – Astrophysics
Scientific paper
1992-12-07
Astron.Astrophys.270:102-106,1993
Astronomy and Astrophysics
Astrophysics
11 pages (using ordinary Latex, 8 using dinA4.sty, 5 using laa.sty) 1 PostScript Figure appended - the rest will be send on re
Scientific paper
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 10^6 M_sun surrounded by an accretion disk which we estimate to radiate at a luminosity of <7 10^5 L_sun. 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 10^4 - 7 10^5 L_sun and T_eff ~ 2-4 10^4 K can be ascribed to a rapidly rotating Kerr~hole (a>0.9) accreting 10^-8.5 - 10^-7 M_sun/yr at a black~hole mass of M=2 10^6 M_sunseen almost edge on. A low mass black hole of M<10^3 M_sun 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.
Biermann Peter L.
Duschl Wolfgang J.
Falcke Heino
Mezger Peter G.
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