Viscosity in Accretion Disks

Abstract

The nature of the viscosity within accretion disks remains one of the greatest uncertainties afflicting models for inflows onto compact objects. Given the presence of even a modicum of angular momentum in the accreting fluid, the strength of the viscosity will have a substantial influence upon the structure of the accretion disk. Unfortunately, under nearly all astrophysically relevant circumstances, all of the well understood microscopic transverse momentum transport mechanisms such as ionic, molecular, and radiative viscosity, are extremely small. Observations with direct relevance to the nature and strength of macroscopic viscosity mechanisms are very difficult to make and their interpretations are model dependent. In the case where a black hole is the compact accretor, such observations have not yet been possible.