Black-Hole Spin Dependence in the Light Curves of Tidal Disruption Events

TL;DR

This paper explores how the spin of a supermassive black hole influences the light curves of tidal disruption events, revealing relativistic effects that alter accretion rates and peak luminosities.

Contribution

It demonstrates that black-hole spin and relativistic effects significantly modify the accretion rate and light curve shape during tidal disruption events.

Findings

Relativistic effects can double the peak accretion rate.

Black-hole spin orientation affects the maximum accretion rate.

Relativistic effects shorten the time to reach peak accretion.

Abstract

A star orbiting a supermassive black hole can be tidally disrupted if the black hole's gravitational tidal field exceeds the star's self gravity at pericenter. Some of this stellar tidal debris can become gravitationally bound to the black hole, leading to a bright electromagnetic flare with bolometric luminosity proportional to the rate at which material falls back to pericenter. In the Newtonian limit, this flare will have a light curve that scales as t^-5/3 if the tidal debris has a flat distribution in binding energy. We investigate the time dependence of the black-hole mass accretion rate when tidal disruption occurs close enough the black hole that relativistic effects are significant. We find that for orbits with pericenters comparable to the radius of the marginally bound circular orbit, relativistic effects can double the peak accretion rate and halve the time it takes to reach this peak accretion rate. The accretion rate depends on both the magnitude of the black-hole spin and its orientation with respect to the stellar orbit; for orbits with a given pericenter radius in Boyer-Lindquist coordinates, a maximal black-hole spin anti-aligned with the orbital angular momentum leads to the largest peak accretion rate.