Structures of AGN Accretion Disks based on Global Radiation MHD Simulations

Abstract: In the standard thin disk model, inner region of the accretion disk is strongly radiation pressure dominated and electron scattering is usually thought to be the dominant opacity. This disk model is known to be thermally unstable and is inconsistent with many observed properties of AGN disks. By performing a series of 3D global radiation MHD simulations, I will show that the very inner region of the disk can end up being primarily supported by magnetic pressure. The formation of coronae in the photosphere of accretion disks is a natural outcome of the accretion process with turbulence generated by magneto-rotational instability. Magnetic fields amplified in the main body of the disks rise up buoyantly and dissipate in the optically thin region, which generates the coronae. Coronae properties and the amount of dissipation that can happen there depend on the detailed structures of the accretion disks. For the radial range 30 to 80 gravitational radii from the black hole, the disk is radiation pressure dominated. However, additional opacity bumps, which can be much larger than the electron scattering opacity, can exist in the disk and change the thermal properties of the disk in this region. It can also cause large amplitude variabilities of the disk luminosity. I will discuss implications of these simulations for understanding various puzzles of AGN observations.

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