Three‐dimensional Simulations of Spherical Accretion Flows with Small‐Scale Magnetic Fields

Spherical (nonrotating) accretion flows with small-scale magnetic fields havebeen investigated using three-dimensional, time-dependent MHD simulations.These simulations have been designed to model high-resolution (quasi) steadyaccretion flows in a wedge computational domain that represents a smallfraction of the full spherical domain. Subsonic and supersonic(super-fast-magnetosonic) accretion flows have been considered. Two accretionregimes have been studied: conservative, or radiatively inefficient, andnonconservative, in which the heat released in magnetic reconnections iscompletely lost. The flows in both regimes are turbulent. They show theflattened radial density profiles and reduction of the accretion velocities andmass accretion rates in comparison with hydrodynamic Bondi flows. In theconservative regime, the turbulence is more intensive and supported mostly bythermal convection. In the nonconservative regime, the turbulence is lessintensive and supported by magnetic buoyancy and various magnetic interactions.We have concluded that steady, supersonic spherical accretion cannot bedeveloped in the presence of small-scale magnetic fields.Comment: 31 pages, 7 figures attached in jpg-format; to appear in Ap