The question whether globular clusters host black holes has been of longstanding interest. This interest has grown dramatically with the LIGO detection of merging black holes, as black hole mergers formed in globular clusters is one of the leading explanations for these LIGO sources. Determining whether black holes are common in globular clusters (GCs) has been an observational challenge. One of the most successful ways to identify candidate black holes in globular clusters is to identify globular cluster X-ray sources with very high luminosities that are much greater than the Eddington limit for a ten solar mass black hole. ULXs in the old GC environment represent a new population of ULXs, and ones likely to be black holes. Currently, 17 ULXs with GC counterparts have been identified. These sources show a diverse behaviour with regards to temporal variability, andhave a potential correlation between X-ray parameters of the sources and the presence of optical emission.
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