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N. Turner, J. Stone (Astronomy Dept., Univ. of Maryland), C. Gammie (Astronomy & Physics Depts., UIUC)
In the central regions of accretion disks around compact objects, radiation pressure may greatly exceed gas pressure. We investigate the Balbus-Hawley or magneto-rotational instability as a possible angular momentum transport mechanism under these conditions. Axisymmetry and shearing-sheet geometry are assumed. Linear analysis indicates that on magnetic fields with a toroidal component, the fastest growth rate is little-changed by diffusion of photons when total magnetic pressure is less than gas pressure. Growth is somewhat slowed when magnetic pressure is between gas and radiation pressures, and much reduced when magnetic pressure is greater than radiation pressure. Slower growth is associated with more compressive perturbed motions, in which kinetic energy is converted into photon energy. In numerical simulations in the flux-limited diffusion approximation, with initially vertical fields of zero net flux, decaying turbulence seen resembles that in gas pressure dominated calculations. The density fluctuations are enhanced when radiation is permitted to diffuse across a wavelength in less than an orbit. These results indicate that magneto-rotational instability may contribute to angular momentum transport and release of energy in the central engines of active galactic nuclei.