Confirmation of an Intermediate-Mass Black Hole in an Extragalactic Globular Cluster

The long and controversial search for black holes within globular clusters has reached the point where extragalactic globular clusters provide fertile hunting grounds for finding black holes of both stellar and intermediate-mass (IMBH) varieties. While a luminous X-ray point source within a cluster can indicate the presence of a black hole, little can generally be said of its mass without further observation. In the event that a black hole tidally disrupts a passing star in the cluster, optical/UV emission lines from the X-ray-illuminated debris can not only demonstrate the existence of a black hole in the cluster, but can also provide powerful constraints on the mass of the black hole, the composition of the disrupted star, and even the time since the tidal disruption event took place. We propose an HST COS G140L UV spectrum of a globular cluster within the Fornax elliptical galaxy NGC1399 that exhibits unusual optical [N II] and [O III] forbidden emission lines that are believed to result from such a tidal disruption event by a 100 solar mass black hole. Our models predict that the ratios of the expected emission lines from carbon, nitrogen, and oxygen that should be present in the UV spectrum of the source will be able to distinguish a stellar-mass black hole from an IMBH as the disruptor, as well as determine the nature of the disrupted star. If the mass of the black hole is constrained to be in excess of 100 solar masses, this would provide one of the most compelling pieces of evidence to date that IMBHs exist within globular clusters.