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The accretion of gas onto black holes powers luminous emission and energetic outflows. Understanding the structure and physics of the gaseous disk is important, so there have been extensive theoretical and numerical studies on accretion disks. Recent studies reveal that in a few important astrophysical systems, the accretion disks have properties very different from standard disks in which the gas carries large angular momentum and the accretion rate is moderate. For example, the infalling gas around Sgr A* likely carries relatively low angular momentum. Also, in tidal disruption events, the debris accretion rate can largely exceed the Eddington accretion rate. Such accretion flows have not been well studied.

I focused on studying these non-standard accretion disks with novel numerical simulations, which can capture the complexity brought by gas hydrodynamics, magnetic fields, radiation and general relativity. In this seminar, I present my two projects. For the first project, I conducted 3D general relativistic magnetohydrodynamic (GRMHD) simulations to study Bondi-like accretion flows with zero or very low specific angular momenta. The simulation results demonstrate that accretion flow needs to initially have a specific angular momentum above a certain threshold to eventually reach and robustly sustain the magnetically arrested disk (MAD) state, which is crucial for launching very powerful jets. For the second project, I conducted 3D radiation GRMHD simulations to study super-Eddington accretion flows. The simulations illustrated how the inflow–outflow structure of super-Eddington accretion flows evolve with accretion rate, and the outputs have been applied to understand the tidal disruption events and AGN feedback.