Global General Relativistic MHD Simulation of a Tilted Black-Hole Accretion Disk

Details Global General Relativistic MHD Simulation of a Tilted Black-Hole Accretion Disk Global General Relativistic MHD Simulation of a Tilted Black-Hole Accretion Disk

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006head....9.0806f&link_type=abstract

American Astronomical Society, HEAD meeting #9, #8.06; Bulletin of the American Astronomical Society, Vol. 38, p.362

Astronomy and Astrophysics

Astronomy

Scientific paper

There are strong theoretical reasons to believe that on large scales many black-hole accretion disks are tilted with respect to the spin axis of the hole, and there is also some observational evidence for this among X-ray binaries (e.g. GRO-J1655-40 & XTE J1550-564). Such disks are subject to a relativistic gravitomagnetic torque causing them to twist and warp. Here we present results of a numerical simulation which fully incorporates the effects of the black hole spacetime as well as magnetorotational turbulence that is thought to be a primary source of angular momentum transport in the flow. We feel this is the most realistic simulation to date of a tilted black-hole accretion disk. This simulation reveals a rich array of phenomena that simply aren't present in untilted disks. Accretion onto the hole occurs predominantly through two opposing plunging streams that start from high latitudes with respect to both the black-hole and disk midplanes. The plunging orbits start from a slightly larger radius than the nominal innermost stable circular orbit (ISCO) radius for prograde orbits in the black-hole symmetry plane. This leaves a larger evacuated volume around the hole than what one observes in simulations of untilted disks. Outside this evacuated region, a prominent inner torus forms at r≈10; GM/c2, aligned virtually in the same plane as the disk at large. Thus there is little indication of a Bardeen-Petterson effect in this simulation, which is consistent with expectations for hot, thick disks such as the one we are simulating. Finally, we observe global precession of the main disk body with a frequency ˜0.3 M/M&sun; s, although we anticipate that this value is strongly dependent on the outer radius of the disk. Our results most likely apply to the low-hard state of black-hole X-ray binaries.

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