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29 March 2024
 
  » arxiv » 1201.4163

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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
AbstractBlack 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
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