On the Vertical Structure of Radiationdominated Accretion Disks
Abstract
The vertical structure of black hole accretion disks in which radiation dominates the total pressure is investigated using a threedimensional radiationMHD calculation. The domain is a small patch of disk centered 100 Schwarzschild radii from a black hole of 10^{8} M_{solar}, and the stratified shearingbox approximation is used. Magnetorotational instability converts gravitational energy to turbulent magnetic and kinetic energy. The gas is heated by magnetic dissipation and by radiation damping of the turbulence, and cooled by diffusion and advection of radiation through the vertical boundaries. The resulting structure differs in several fundamental ways from the standard ShakuraSunyaev picture. The disk consists of three layers. At the midplane, the density is large, and the magnetic pressure and total accretion stress are less than the gas pressure. In lower density surface layers that are optically thick, the magnetic pressure and stress are greater than the gas pressure but less than the radiation pressure. Horizontal density variations in the surface layers exceed an order of magnitude. Magnetic fields in the regions of greatest stress are buoyant, and dissipate as they rise, so the heating rate declines more slowly with height than the stress. Much of the dissipation occurs at low column depth, and the interior is cooler and less radiationdominated than in the ShakuraSunyaev model with the same surface mass density and flux. The mean structure is convectively stable.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 2004
 DOI:
 10.1086/386545
 arXiv:
 arXiv:astroph/0402539
 Bibcode:
 2004ApJ...605L..45T
 Keywords:

 Accretion;
 Accretion Disks;
 Instabilities;
 Magnetohydrodynamics: MHD;
 Radiative Transfer;
 Astrophysics
 EPrint:
 3 figures. Accepted by Astrophysical Journal Letters