Cosmological Mestel Disks and the Rossby Vortex Instability: The Origin of Supermassive Black Holes

Abstract

A scenario is put forth for the formation of supermassive black holes at the centers of galaxies. It depends upon the formation of a Mestel disk with a flat rotation curve, where the mass is proportional to r and thickness to 1/r. Such disks should form from the collapse of uniformly rotating, isolated, gaseous clouds, either proto-galactic, galaxy-mass damped Lyman alpha clouds or the gas that survives galaxy mergers. We propose that in any case the disk will be unstable to the Rossby vortex instability (RVI). This instability grows from any large, steep pressure gradient in an optically thick disk. Such pressure gradients either occur adjacent to compact objects or could be triggered by individual supernovae in and around the disk. Upon excitation, the RVI transports angular momentum far more efficiently than the turbulence of a viscosity-based Shakura-Sunyaev disk. The critical column density condition in a L* Mestel disk predicts that the black hole mass is ~ 10^8 Msolar and is also proportional to the 1/4 power of the velocity dispersion, in accordance with observations.