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Heino Falcke

Publications and source records attributed to Heino Falcke.

218 records · Page 13Linked to original sources

The Galactic Center radio jet

Recent observations of the radio and NIR source Sgr A* reinforce the interpretation of the Galactic Center as a scaled down version of an AGN. The discovery of an elongated structure at 43 GHz and increasing evidence for the presence of an accretion disk surrounding a Black Hole lead us to assume that both, an accretion disk and a jet, are present in the Galactic Center and are physically linked. We model the radio emission of Sgr A* successfully with a Blandford & K"onigl type jet and analyze the energetics of the coupled jet-disk system in Sgr A* where jet and disk are parametrized in terms of the accretion power. With this method we are able to confirm independently the lower limit of the Sgr A* accretion rate \dot M >> 10^-8.5 M_sun found previously. Moreover, using the limits imposed by observational data, we show that within such a jet-disk model, the total jet power Q_jet is of comparable order as the radiated disk luminosity L_disk. A jet model together with the assumption of an 10^6 M_sun Black Hole also qualitatively explains the submm excess and the lack of non-thermal IR radiation. The small size of the visible part of the jet (< 1 mas) is due to the low accretion rate of Sgr A*. << >>

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A rotating black hole in the Galactic Center

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.

astro-ph↗