Evidence for a Stellar Disruption by an IMBH in an Extragalactic Globular Cluster

TL;DR

This paper presents evidence suggesting a stellar tidal disruption by an intermediate-mass black hole in a globular cluster, inferred from specific emission lines and their properties, indicating a black hole of at least 1000 solar masses.

Contribution

It provides observational evidence for a stellar disruption event caused by an intermediate-mass black hole in an extragalactic globular cluster, highlighting unique emission line signatures.

Findings

Detection of forbidden emission lines without Balmer lines.

Minimum black hole mass estimated at 1000 solar masses.

Indication of white dwarf disruption based on spectral features.

Abstract

We report [O III] 5007 Angstrom and [N II] 6583 Angstrom emission from a globular cluster harboring the ultraluminous X-ray source (ULX) CXOJ033831.8-352604 in the Fornax elliptical galaxy NGC1399. No accompanying Balmer emission lines are present in the spectrum. One possibility is that the forbidden lines emanate from X-ray illuminated debris of a star that has been tidally-disrupted by an intermediate-mass black hole (IMBH), with this debris also feeding the black hole leading to the observed X-ray emission. The line strengths indicate that the minimum size of the emitting region is ~10^15 cm, and if the 70 km/s half-widths of the emission lines represent rotation around the black hole, a minimum black hole mass of 1000 solar mass is implied. The non-detection of H-alpha and H-beta emission lines suggests a white dwarf star was disrupted, although the presence of strong nitrogen emission is somewhat of a mystery.