Three‐dimensional Magnetohydrodynamic Simulations of Radiatively Inefficient Accretion Flows

We present three-dimensional MHD simulations of rotating radiativelyinefficient accretion flows onto black holes. In the simulations, wecontinuously inject magnetized matter into the computational domain near theouter boundary, and we run the calculations long enough for the resultingaccretion flow to reach a quasi-steady state. We have studied two limitingcases for the geometry of the injected magnetic field: pure toroidal field andpure poloidal field. In the case of toroidal field injection, the accretingmatter forms a nearly axisymmetric, geometrically-thick, turbulent accretiondisk. The disk resembles in many respects the convection-dominated accretionflows found in previous numerical and analytical investigations of viscoushydrodynamic flows. Models with poloidal field injection evolve through twodistinct phases. In an initial transient phase, the flow forms a relativelyflattened, quasi-Keplerian disk with a hot corona and a bipolar outflow.However, when the flow later achieves steady state, it changes in charactercompletely. The magnetized accreting gas becomes two-phase, with most of thevolume being dominated by a strong dipolar magnetic field from which a thermallow-density wind flows out. Accretion occurs mainly via narrow slowly-rotatingradial streams which `diffuse' through the magnetic field with the help ofmagnetic reconnection events.Comment: 35 pages including 3 built-in plots and 14 separate jpg-plots; version accepted by Ap