Publication date: Sep 2008
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.
Stuchlík, Zdenĕk; Slaný, Petr; Török, Gabriel;