Publication date: Sep 2008
Abstract:
Humpy LNRF-velocity profiles were found for both Keplerian thin discs and marginally stable thick discs orbiting almost extreme Kerr black holes, being located just above the innermost stable circular orbit. In thick marginally stable discs, the global character of this phenomenon is given by topology changes of equivelocity (von Zeipel) surfaces, as the standard cylindrical von Zeipel surfaces are transformed into toroidal surfaces existing around the circle corresponding to the local minimum of the equatorial humpy LNRF-velocity profile. These phenomena could indicate an instability in the disc triggering so-called „humpy“ oscillations, the frequency of which is estimated by the maximum positive gradient of the humpy velocity profile in terms of the proper radial distance. The humpy oscillations could force epicyclic oscillations, if appropriate resonance conditions are satisfied.
Authors:
Stuchlík, Zdenĕk; Slaný, Petr; Török, Gabriel;