Accretion disks around kicked black holes: Post-kick Dynamics

TL;DR

This study uses simulations to explore how black holes receiving a sudden velocity boost affect their surrounding accretion disks, revealing the impact of kick angle on disk structure and luminosity.

Contribution

It provides the first detailed analysis of post-kick accretion disk dynamics considering different kick angles using smoothed particle hydrodynamics simulations.

Findings

Vertical kicks preserve an inner disk gap.

Oblique kicks cause rapid matter accretion.

Higher luminosity potential for more oblique kicks.

Abstract

Numerical calculations of merging black hole binaries indicate that asymmetric emission of gravitational radiation can kick the merged black hole at up to thousands of km/s, and a number of systems have been observed recently whose properties are consistent with an active galactic nucleus containing a supermassive black hole moving with substantial velocity with respect to its broader accretion disk. We study here the effect of an impulsive kick delivered to a black hole on the dynamical evolution of its accretion disk using a smoothed particle hydrodynamics code, focusing attention on the role played by the kick angle with respect to the orbital angular momentum vector of the pre-kicked disk. We find that for more vertical kicks, for which the angle between the kick and the normal vector to the disk $\theta\lesssim 30^\circ$, a gap remains present in the inner disk, in accordance with the prediction from an analytic collisionless Keplerian disk model, while for more oblique kicks with $\theta\gtrsim 45^\circ$, matter rapidly accretes toward the black hole. There is a systematic trend for higher potential luminosities for more oblique kick angles for a given black hole mass, disk mass and kick velocity, and we find large amplitude oscillations in time in the case of a kick oriented $60^\circ$ from the vertical.