Resonant friction on discs in galactic nuclei

Abstract

We argue that resonant friction has a dramatic effect on a disc whose rotation direction is misaligned with that of its host nuclear star cluster. The disc's gravity causes gravitational perturbation of the cluster that in turn exerts a strong torque back onto the disc. We argue that this torque may be responsible for the observed disruption of the clockwise disc of young stars in the Galactic Center, and show in numerical experiments that it produces the observed features in the distribution of the stars' angular momenta. More generally, we speculate that the rotation of nuclear star clusters has a stabilizing effect on the orientation of transient massive accretion discs around the supermassive black holes residing in their centers, and thus on the directions and magnitudes of the black-hole spins.