Tidal Disruption of a Main-Sequence Star by an Intermediate-Mass Black Hole: A Bright Decade

TL;DR

This paper models the long-term observational signatures of tidal disruption events of main-sequence stars by intermediate-mass black holes, predicting UV/optical outbursts and X-ray emissions that could help identify elusive IMBHs.

Contribution

It provides a detailed theoretical framework for the accretion and emission processes in IMBH tidal disruption events, including the first modeling of a candidate event.

Findings

Super-Eddington accretion phase lasts about 10 years.

Peak emission occurs in UV/optical bands with luminosity ~10^42 erg/s.

X-ray emission appears after the accretion rate drops below Eddington.

Abstract

There has been suggestive evidence of intermediate-mass black holes (IMBHs; 10^{3-5} M_sun) existing in some globular clusters (GCs) and dwarf galaxies, but IMBHs as a population remain elusive. As a main-sequence star passes too close by an IMBH it might be tidally captured and disrupted. We study the long-term accretion and observational consequence of such tidal disruption events. The disruption radius is hundreds to thousands of the BH's Schwarzschild radius, so the circularization of the falling-back debris stream is very inefficient due to weak general relativity effects. Due to this and a high mass fallback rate, the bound debris initially goes through a ~10 yr long super-Eddington accretion phase. The photospheric emission of the outflow ejected during this phase dominates the observable radiation and peaks in the UV/optical bands with a luminosity of 10^42 erg/s. After the accretion rate drops below the Eddington rate, the bolometric luminosity follows the conventional t^{-5/3} power-law decay, and X-rays from the inner accretion disk start to be seen. Modeling the newly reported IMBH tidal disruption event candidate 3XMM J2150-0551, we find a general consistency between the data and predictions. The search for these luminous, long-term events in GCs and nearby dwarf galaxies could unveil the IMBH population.