On the Vertical Structure of Radiation-Supported Accretion Disks

The vertical structure of a black hole accretion disk in which radiation dominates the total pressure is investigated using a three-dimensional radiation-MHD calculation, in the stratified shearing-box approximation. Magneto-rotational instability [Balbus, S. A. and Hawley, J. F., Astrophys. J. 376 (1991), 214] converts differential rotation to turbulent magnetic and kinetic energy. The gas is cooled by diffusion and advection of radiation through the vertical boundaries. Density is greatest near the midplane, while accretion stresses are greatest in optically-thick surface layers. The thermal time, and the ratio of radiation to gas pressure, are an order of magnitude smaller than in the corresponding Shakura-Sunyaev model [Shakura, N. I. and Sunyaev R. A., Astron. Astrophys. 24 (1973), 337] because dissipation occurs at low column density.