Tidal Disruption Events by Compact Supermassive Black Hole Binaries

TL;DR

This study uses extensive simulations to analyze how supermassive black hole binaries influence tidal disruption events, revealing significant enhancement or suppression effects depending on binary parameters and providing a practical formula for disruption probabilities.

Contribution

It extends previous work by exploring a broader parameter space and offers a fitting formula for disruption probabilities in supermassive black hole binaries.

Findings

Full disruption probability can be increased by up to 50 times or decreased by 10 times.

Partial disruptions can occur multiple times, affecting stellar properties and event rates.

Relativistic effects are minor for black holes with mass ≤ 10^7 solar masses.

Abstract

Stars can be tidally destroyed or swallowed by supermassive black hole binaries. Using a large number of accurate few-body simulations, we investigate the enhancement and suppression of full and partial disruption and direct capture events by hard supermassive black hole binaries with a wide ranges of key parameters, i.e., the primary black hole mass ($10^{5}-10^{8}M_{\odot}$), the binary mass ratio ($10^{-3}-1$), the ratio of the binary semimajor axis to the hardening radius ($10^{-4}-1$), the binary eccentricity ($0.0-0.9$) and the stellar mass ($0.3-3M_{\odot}$). This is a significant extension of the parameter space compared to previous work. We show that the encounter probabilities of all three events are well-described by the encounter cross section, which is proportional to the pericenter distance. The probability of full disruptions by supermassive black hole binaries can be enhanced by up to a factor of $40-50$ or suppressed by up to a factor of $10$, relative to that by single black holes, depending on the binary parameters. Relativistic effects are not important for the primary black hole mass $\leq 10^{7}M_{\odot}$, but can provide an additional enhancement of the full disruption probability by less than a factor of $2-3$ for higher primary black hole masses. We provide a fitting formula for the full disruption probability by the hard supermassive black hole binaries that works for a wide range of parameters. We also find that partial disruption events can occur multiple times before full disruptions or direct captures, and their probabilities can be greater than that of full disruption events by a factor of three. Because partial disruption events can induce stellar spins and mass loss and change the orbits, it can significantly affect the overall full disruption event rate and the shape of the light curves.