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

full text pdf, accepted to MNRAS 18th June 2013 (arXiv:1307.0010)

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Abstract

In a recent paper we have shown that the evolution of a misaligned disc around a spinning black hole can result in tearing the disc into many distinct planes. Tearing discs with random orientations produce direct dynamical accretion on to the hole in 70% of all cases. Here we examine the evolution of a misaligned disc around a binary system. We show that these discs are susceptible to tearing for almost all inclinations. We also show that tearing of the disc can result in a significant acceleration of the disc evolution and subsequent accretion on to the binary by factors up to 10⁴ times that of a coplanar prograde disc with otherwise identical parameters. This provides a promising mechanism for driving mergers of supermassive black hole (SMBH) binaries on timescales much shorter than a Hubble time. Disc tearing also suggests new observational signatures of accreting SMBH binaries, and other systems such as protostellar binaries.

Movies Created using SPLASH. See also Chris Nixon's tearing discs page.	Movies and images (c) 2013 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 binary black hole system where the disc is misaligned with respect to the binary by 45 degrees. The precession caused by the binary 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. Direct accretion onto the binary results an eccentric disc of material being "splatted" by the binary. Note the formation of circumprimary and circum-secondary discs around the two black holes. Download binary_med_theta45.mp4
	As above, but with a 60 degree misalignment. Download binary_med_theta60.mp4
	No misalignment - this is what happens when both the accretion disc and the binary black holes orbit in the same plane. Nothing much happens except that the binary excites resonances in the inner disc material (a resonance is where orbital periods that are exact multiples of the binary period get an extra "kick"). Download binary_med_theta0.mp4
	Complete counter-alignment. In this case the disc and the stars rotate in opposing directions. This is very similar to the co-aligned case, the main difference being that there are no resonances in this case, so the inner disc evolution is not excited by the binary. Even less happens. Download binary_med_theta180.mp4
	120 degree misalignment. Note the temporary formation of miniature circum-primary and circum-secondary discs around the two black holes. Download binary_med_theta120.mp4
	135 degree misalignment. Download binary_med_theta135.mp4
	150 degree misalignment. Download binary_med_theta150.mp4
	30 degree misalignment. Download binary_med_theta30.mp4