On the Bardeen–Petterson effect in black hole accretion discs

Abstract

We investigate the effect of black hole spin on warped or misaligned accretion discs -in particular i) whether or not the inner disc edge aligns with the black hole spin and ii) whether the disc can maintain a smooth transition between an aligned inner disc and a misaligned outer disc, known as the Bardeen-Petterson effect. We employ high resolution 3D smoothed particle hydrodynamics simulations of α-discs subject to Lense-Thirring precession, focussing on the bending wave regime where the disc viscosity is smaller than the aspect ratio α H/R. We first address the controversy in the literature regarding possible steady-state oscillations of the tilt close to the black hole. We successfully recover such oscillations in 3D at both small and moderate inclinations ( 15 • ), provided both Lense-Thirring and Einstein precession are present, sufficient resolution is employed, and provided the disc is not so thick so as to simply accrete misaligned. Second, we find that discs inclined by more than a few degrees in general steepen and break rather than maintain a smooth transition, again in contrast to previous findings, but only once the disc scale height is adequately resolved. Finally, we find that when the disc plane is misaligned to the black hole spin by a large angle, the disc 'tears' into discrete rings which precess effectively independently and cause rapid accretion, consistent with previous findings in the diffusive regime (α H/R). Thus misalignment between the disc and the spin axis of the black hole provides a robust mechanism for growing black holes quickly, regardless of whether the disc is thick or thin.

Spacetime, spin and Gravity Probe B

“…Frame-dragging causes the disk to precess around the black hole, and this precession combines with the disk's viscosity to drive the inner region of the disk into the black hole's equatorial plane, so that the jets gradually become aligned with the spin axis of the black hole. This phenomenon, known as the Bardeen-Petterson effect [54,55], has been verified by detailed three-dimensional numerical simulations [56,57].…”

Space Telescope and Optical Reverberation Mapping PROJECT.VI. Reverberating Disk Models for NGC 5548

“…This will also give rise to the large time lags we see in Figure 7 relative to the driving light curve, since photons require multiple light-travel paths before intercepting the accretion disk. Another interpretation is that the inner disk is tilted relative to the outer disk, aligning itself with the spin of the black hole inward of some radius (Nealon et al 2015). The implication of this interpretation is that the driving light curve is actually just the emission from the inner tilted disk.…”

Circumbinary, not transitional: on the spiral arms, cavity, shadows, fast radial flows, streamers, and horseshoe in the HD 142527 disc

“…This is consistent with the estimated inclination of the inner binary with respect to the disc (L16). Perhaps the greatest surprise were the complexities found in detailed kinematic studies using CO(6-5) molecular line data by Casassus et al (2015a), with evidence for a warped disc and near free-fall motions within the central cavity, suggested to be related to theoretical models of 'disc tearing' in warped accretion discs (Nixon et al 2013;Nealon et al 2015).…”