Abstract
The phenomena observed in AGNs, especially the more extreme manifestations, are widely attributed to processes around black holes. It would therefore be gratifying if the case for black holes became less circumstantial than it now is. The most straightforward dynamical evidence comes from stellar motions in nearby galaxies with quiescent nuclei, which indicate dark central mass concentrations. This subject has been described by Kormendy at this meeting. If black holes are indeed present in these nearby nuclei, their quiescence implies that accretion of gas is proceeding very slowly, and/or is very inefficient radiatively. However, there is one process which would inevitably, now and again, release gas very close to the hole: tidal disruption of stars on nearly radial orbits. The rate of such events depends on the parameters of the central star cluster, which determine the rate at which dynamical processes cause stars to ‘diffuse’ onto nearly radial orbits. A rough estimate, based on models for the stellar cusp, suggests that in M31 a main-sequence star would pass close enough to the putative hole to be tidally disrupted about once every 104 years.
Published Version
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