Two‐dimensional Hydrodynamic Simulations of Convection in Radiation‐dominated Accretion Disks

The standard equilibrium for radiation-dominated accretion disks has longbeen known to be viscously, thermally, and convectively unstable, but thenonlinear development of these instabilities---hence the actual state of suchdisks---has not yet been identified. By performing local two-dimensionalhydrodynamic simulations of disks, we demonstrate that convective motions canrelease heat sufficiently rapidly as to substantially alter the verticalstructure of the disk. If the dissipation rate within a vertical column isproportional to its mass, the disk settles into a new configuration thinner bya factor of two than the standard radiation-supported equilibrium. If, on theother hand, the vertically-integrated dissipation rate is proportional to thevertically-integrated total pressure, the disk is subject to the well-knownthermal instability. Convection, however, biases the development of thisinstability toward collapse. The end result of such a collapse is a gaspressure-dominated equilibrium at the original column density.Comment: 10 pages, 7 figures, accepted for publication in ApJ. Please send comments to agol@tapir.caltech.ed