Super-Eddington Accretion Disks around Supermassive Black Holes

Abstract

Abstract We use global three-dimensional radiation magnetohydrodynamical simulations to study accretion disks onto a black hole with accretion rates varying from to . We initialize the disks with a weakly magnetized torus centered at either 50 or 80 gravitational radii, leading to self-consistent turbulence generated by the magnetorotational instability (MRI). The inner regions of all disks have radiation pressure ∼104–106 times the gas pressure. Nonaxisymmetric density waves that steepen into spiral shocks form as gas flows toward the black hole. Maxwell stress from MRI turbulence can be larger than the Reynolds stress only when the net vertical magnetic flux is sufficiently large. Outflows are formed with a speed of ∼0.1–0.4c. When the accretion rate is smaller than , outflows are launched from ∼10 gravitational radii, and the radiative efficiency is ∼5%–7%. For an accretion rate reaching , most of the funnel region near the rotation axis becomes optically thick, and the outflow is launched from beyond 50 gravitational radii. The radiative efficiency is reduced to 1%. We always find that the kinetic energy luminosity associated with the outflow is at most ∼15%–30% of the radiative luminosity. The mass flux in the outflow is ∼15%–50% of the net mass accretion rates. We discuss the implications of our simulation results on the observational properties of these disks.