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General Relativistic Magnetohydrodynamic Simulations of Magnetically Choked Accretion Flows around Black Holes | Jonathan C. McKinney
; Alexander Tchekhovskoy
; Roger D. Blandford
; | Date: |
19 Jan 2012 | Abstract: | 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 $ ausim 70GM/c^3$ for
$a/Msim 0.9$ with quality factor $Qsim 100$ in the jet, $Qsim 10$ at one
disk scale-height, and $Qsim 3$ in the disk plane [abridged]. | Source: | arXiv, 1201.4163 | Services: | Forum | Review | PDF | Favorites |
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