A New Equilibrium for Accretion Disks around Black Holes

Accretion disks around black holes in which the shear stress is proportionalto the total pressure, the accretion rate is more than a small fraction ofEddington, and the matter is distributed smoothly are both thermally andviscously unstable in their inner portions. The nonlinear endstate of theseinstabilities is uncertain. Here a new inhomogeneous equilibrium is proposedwhich is both thermally and viscously stable. In this equilibrium the majorityof the mass is in dense clumps, while a minority reaches temperatures $\sim10^9$ K. The requirements of dynamical and thermal equilibrium completelydetermine the parameters of this system, and these are found to be in goodagreement with the parameters derived from observations of accreting blackholes, both in active galactic nuclei and in stellar binary systems.Comment: AAS LaTeX, accepted to Ap. J. Letter