Apsidal precession, disc breaking and viscosity in warped discs

Rebecca Nealon,Andrew King,Chris Nixon,Daniel J Price

doi:10.1093/mnrasl/slv149

Abstract

Abstract We demonstrate the importance of general relativistic apsidal precession in warped black hole accretion discs by comparing three-dimensional smoothed particle hydrodynamic simulations in which this effect is first neglected, and then included. If apsidal precession is neglected, we confirm the results of an earlier magnetohydrodynamic simulation which made this assumption, showing that at least in this case the α viscosity model produces very similar results to those of simulations where angular momentum transport is due to the magnetorotational instability. Including apsidal precession significantly changes the predicted disc evolution. For moderately inclined discs thick enough that tilt is transported by bending waves, we find a disc tilt which is non-zero at the inner disc edge and oscillates with radius, consistent with published analytic results. For larger inclinations, we find disc breaking.

Highlights

Bardeen & Petterson (1975) first studied accretion discs misaligned with the spin of a central black hole
The start of the simulation is marked by a sharp disturbance in the tilt and surface density profiles as the black hole torque is applied, but this wave damps within 4.5 orbits and the rest of the disc evolution is gradual
Our disc evolves in the same manner described by KH15; the inner edge aligns with the spin of the black hole, and there is a smooth transition to the outer region which remains misaligned

Summary

Introduction

Bardeen & Petterson (1975) first studied accretion discs misaligned with the spin of a central black hole. The Lense–Thirring effect causes the disc to warp, so that the inclination between the local disc plane and the black hole spin varies as a function of radius. Papaloizou & Pringle (1983) identified two regimes that govern the propagation of warps, determined by comparing the dimensionless viscosity parameter α (Shakura & Sunyaev 1973) to the aspect ratio H/R, where H is the disc scaleheight and R the radius. When α H/R, warps propagate as bending waves that travel at half the sound speed (Papaloizou & Lin 1995). Papaloizou & Terquem (1995) showed that the disc can warp significantly when the sound crossing time is longer than the induced precession time. See Nixon & King (2015) for a recent review of warped disc dynamics

Results

Discussion

Conclusion