Chris J. Nixon, Andrew R. King, Daniel J. Price, Juhan Frank

full text pdf (200Kb), accepted to ApJL 17th August 2012

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Abstract

We show that in realistic cases of accretion in active galactic nuclei or stellar-mass X-ray binaries, the Lense-Thirring effect breaks the central regions of tilted accretion discs around spinning black holes into a set of distinct planes with only tenuous flows connecting them. If the original misalignment of the outer disc to the spin axis of the hole is, as in of randomly oriented accretion events, the continued precession of these discs sets up partially counter-rotating gas flows. This drives rapid infall as angular momentum is cancelled and gas attempts to circularize at smaller radii. Disc breaking close to the black hole leads to direct dynamical accretion, while breaking further out can drive gas down to scales where it can accrete rapidly. For smaller tilt angles breaking can still occur, and may lead to other observable phenomena such as QPOs. For such effects not to appear, the black hole spin must in practice be negligibly small, or be almost precisely aligned with the disc. Qualitatively similar results hold for any accretion disc subject to a forced differential precession, such as an external disc around a misaligned black hole binary.

Movies Created using SPLASH. See also Chris Nixon's tearing discs page.	Movies and images (c) 2012 Chris Nixon, released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License. [directory listing of all movies here]
	Response of an accretion disc around a black hole in the case where the disc is misaligned with respect to the spin of the black hole by a "large" tilt (60 degrees). In this case the Lense-Thirring precession caused by the black hole spin exerts a greater torque on the disc than the viscous torques trying to bring the disc into alignment, causing the disc to break. The broken rings precess until they are counter-aligned with respect to the original disc, at which point the opposing angular momenta cancel and "direct" accretion of the ring occurs. Download NKPF12-tearing-large.mp4
	As above, but showing column density (integrated line-of-sight density) rather than the surface rendering shown above. Download NKPF12-tearing-large-cd.mp4
	Response of an accretion disc around a black hole in the case where the disc is misaligned with respect to the spin of the black hole by a "small" tilt (10 degrees). In this case the torque due to Lense-Thirring precession caused by the black hole spin is less than than the viscous torques, and the disc is able to make a smooth transition across the warp radius. Download NKPF12-tearing-small.mp4
	As above, but showing column density instead of the 3D rendering. Download NKPF12-tearing-small-cd.mp4
	Another version of the large tilt calculation, from a slightly different perspective. Download NKPF12-tearingdisc.mp4