General Relativistic Magnetohydrodynamic Simulations of Magnetically Choked Accretion Flows Around Black Holes.

摘要

Black hole (BH) accretion flows and jets are qualitatively affected by the presence of ordered magnetic fields. We study fully three-dimensional global general relativistic magnetohydrodynamic (MHD) simulations of radially extended and thick (height H to cylindrical radius R ratio of (vertical bar) H/R(vertical bar) (approx) 0.2-1) accretion flows around BHs with various dimensionless spins (a/M, with BH mass M) and with initially toroidally-dominated ((phi)-directed) and poloidally-dominated (R-z directed) magnetic fields. Firstly, for toroidal field models and BHs with high enough (vertical bar)a/M(vertical bar), coherent large-scale (i.e. >> H) dipolar poloidal magnetic flux patches emerge, thread the BH, and generate transient relativistic jets. Secondly, for poloidal field models, poloidal magnetic flux readily accretes through the disk from large radii and builds-up to a natural saturation point near the BH. While models with (vertical bar)H/R(vertical bar) (approx) 1 and (vertical bar)a/M(vertical bar) (le) 0.5 do not launch jets due to quenching by mass infall, for sufficiently high (vertical bar)a/M(vertical bar) or low (vertical bar)H/R(vertical bar) the polar magnetic field compresses the inflow into a geometrically thin highly non-axisymmetric 'magnetically choked accretion flow' (MCAF) within which the standard linear magneto-rotational instability is suppressed.