Leipzig 2002 – scientific programme

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SYSL: Schwarze Löcher

SYSL II: HV II

SYSL II.1: Invited Talk

Tuesday, March 19, 2002, 14:45–15:30, HS 20

Black holes are slippery — •Marek A. Abramowicz — Chalmers University, Göteborg, Sweden

I discuss some fundamental properties of circular orbits of test particles around black holes that have not been recognized previously. In particular, I discuss the direct astrophysical importance of anharmonic and parametric resonances between radial and polar epicyclic frequencies in circular motion. I also discuss the behaviour of shear and vorticity in matter on circular orbits very close to the horizon and show that exact analytic results imply that the viscous torque between matter and black hole must vanish, contrary to some recent claims based on an extrapolation of approximate numerical models. Thus, in the sense of vanishing viscous torque, black holes are perfectly slippery.