Viscous drag on an accretion disk due to an embedded stellar system

Abstract

A torque that removes angular momentum from gaseous disks (such as accretion disks) may result from their embedding in a more massive stellar system as a result of interactions between the stars and the gas, with a drag time at any radius that is of the order of the relaxation time in the stellar system irrespective of disk properties. Calculations are presented for the isotropic distribution that is believed to form about a black hole, and for the isothermal Maxwellian distribution. A speculative scenario is presented in which a dense stellar system might simulate many of the properties of an active galactic nucleus without invoking a central black hole. Generally, the present results are of consequence for active galactic nuclei involving the accretion of gas onto central black holes.