Jonathan C. McKinney, Alexander Tchekhovskoy, Roger D. Blandford
Black hole (BH) accretion flows and jets are qualitatively affected by the
presence of ordered magnetic fields. We describe fully three-dimensional global
general relativistic magnetohydrodynamic (MHD) simulations of radially extended
and thick (height $H$ to cylindrical radius $R$ ratio of $|H/R|\sim 0.2--1$)
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. For initially
toroidally-dominated magnetic field models, patches of spontaneously generated
coherent large-scale dipolar magnetic flux do reach the BH but only lead to
transient mildly relativistic winds and weak relativistic jets. For initially
poloidally-dominated magnetic field models, poloidal magnetic flux readily
accretes through the disk from large radii and builds-up to a natural
saturation point near the BH. For sufficiently high $|a/M|$ or low $|H/R|$ the
polar magnetic field compresses the thick flow into a geometrically thin highly
non-axisymmetric magnetically choked accretion flow (MCAF) within which the
magneto-rotational instability is suppressed. The condition of a
highly-magnetized state over most of the horizon is optimal for the
Blandford-Znajek mechanism that generates persistent relativistic jets with
$\gtrsim 100$% efficiency for $|a/M|\gtrsim 0.9$. The compressed disk inflow
interacts with the jet magnetosphere driving a new jet-disk oscillation (JDO)
type of quasi-periodic oscillation (QPO) mechanism leading to high-frequency
QPOs with spherical harmonic $|m|=1$ mode period of $\tau\sim 70GM/c^3$ for
$a/M\sim 0.9$ with quality factor $Q\sim 100$ in the jet, $Q\sim 10$ at one
disk scale-height, and $Q\sim 3$ in the disk plane [abridged].
View original:
http://arxiv.org/abs/1201.4163
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