Shock-induced partial alignment in geometrically-thick tilted accretion disks around black holes

Abstract

We carry out idealized three-dimensional general-relativistic magnetohydrodynamic (GRMHD) simulations of prograde, weakly magnetized, and geometrically thick accretion flows where the gas distribution is misaligned from the black hole spin axis. We evolve the disk for three black hole spins: $a=0.5,0.75$, and $0.9375$, and we contrast them with a standard aligned disk simulation with $a=0.9375$. The tilted disks achieve a warped and twisted steady-state structure, with the outer disk misaligning further away from the black hole and surpassing the initial $24^{\circ }$ misalignment. However, closer to the black hole, there is evidence of partial alignment, as the inclination angle decreases with radius in this regime. Standing shocks also emerged in proximity to the black hole, roughly at $\sim$ 6 gravitational radii. We show that these shocks act to partially align the inner disk with the black hole spin. The rate of alignment increases with increasing black hole spin magnitude, but in all cases is insufficient to fully align the gas before it accretes. Additionally, we present a toy model of orbit crowding that can predict the location of the shocks in moderate-to-fast rotating black holes, illustrating a potential physical origin for the behavior seen in simulations\textemdash with possible applications in determining the positions of shocks in real misaligned astrophysical systems.

17 pages, 11 figures, 1 Table and accepted for publication in ApJ

References in corpus (12)

• Array Programming with NumPy
• Advection-Dominated Accretion and the Black Hole Event Horizon
• Global General Relativistic MHD Simulation of a Tilted Black-Hole Accretion Disk
• Alignment of Magnetized Accretion Disks and Relativistic Jets with Spinning Black Holes
• On the Bardeen-Petterson Effect in black hole accretion discs
• Black hole-neutron star binary merger: Dependence on black hole spin orientation and equations of state
• Precessing jet nozzle connecting to a spinning black hole in M87
• Epicyclic Motions and Standing Shocks in Numerically Simulated Tilted Black-Hole Accretion Disks
• Radiation GRMHD Simulations of the Hard State of Black Hole X-ray Binaries and the Collapse of a Hot Accretion Flow
• Tilted Disks around Black Holes: A Numerical Parameter Survey for Spin and Inclination Angle
• Conservative GRMHD Simulations of Moderately Thin, Tilted Accretion Disks
• No Evidence for Bardeen-Petterson Alignment in GRMHD Simulations and Semi-Analytic Models of Moderately Thin, Prograde, Tilted Accretion Disks