Tidal disruption events by compact supermassive black hole binaries

Abstract

ABSTRACT Stars can be tidally destroyed or swallowed by supermassive black hole binaries (SMBHBs). Using a large number of few-body simulations, we investigate the enhancement and suppression of full and partial disruption and direct capture events by hard SMBHBs with wide ranges of key parameters, i.e. the primary BH mass ($M_{\rm BH, 1}= 10^{5}{-}10^{8}\, {\rm M}_{\odot }$), 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 $(0.3{-}3\, {\rm M}_{\odot})$. 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. The probability of full tidal disruption events (FTDEs) by SMBHBs 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 BHs, depending on the binary parameters. Relativistic effects can provide an additional enhancement of the FTDE probability by less than a factor of 2–3 for $M_{\rm BH, 1}> 10^{7}\, {\rm M}_{\odot }$. We provide a fitting formula for the FTDE probability by SMBHBs that works for a wide range of parameters. Partial disruption events can occur multiple times before FTDEs or direct captures, and their probabilities can be greater than that of FTDEs 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 FTDE rate and the shape of the light curves.