Partial tidal disruption events by stellar mass black holes: gravitational instability of stream and impact from remnant core

TL;DR

This study investigates partial tidal disruption events caused by stellar mass black holes in dense star clusters, revealing how fallback rates depend on black hole mass and how stream instabilities affect accretion signatures.

Contribution

The paper introduces a new method for calculating fallback rates and demonstrates the impact of stream instabilities and remnant cores on TDEs involving stellar mass black holes.

Findings

Fallback rate slope depends on black hole mass.

Stream self-gravity causes clump formation before fallback.

Fallback rate can deviate from a simple powerlaw.

Abstract

In dense star clusters, such as globular and open clusters, dynamical interactions between stars and black holes (BHs) can be extremely frequent, leading to various astrophysical transients. Close encounters between a star and a stellar mass BH make it possible for the star to be tidally disrupted by the BH. Due to the relative low mass of the BH and the small cross section of the tidal disruption event (TDE) for cases with high penetration, disruptions caused by close encounters are usually partial disruptions. The existence of the remnant stellar core and its non-negligible mass compared to the stellar mass BH alters the accretion process significantly. We study this problem with SPH simulations using the code {\tt Phantom}, with the inclusion of radiation pressure, which is important for small mass BHs. Additionally, we develop a new, more general method of computing the fallback rate which does not rely on any approximation. Our study shows that the powerlaw slope of the fallback rate has a strong dependence on the mass of the BH in the stellar mass BH regime. Furthermore, in this regime, self-gravity of the fallback stream and local instabilities become more significant, and cause the disrupted material to collapse into small clumps before returning to the BH. This results in an abrupt increase of the fallback rate, which can significantly deviate from a powerlaw. Our results will help in the identification of TDEs by stellar mass BHs in dense clusters.