Xray obs. of gal. hosting nuclear star clusters

NSCs are extremely dense stellar environments with conditions that can theoretically facilitate massive BH formation. Recent work by Stone+ (2017MNRAS.467.4180S) finds that sufficiently dense NSCs should be unstable to the runaway growth of a stellar-mass BH into a massive BH via tidal captures.

Furthermore, there is a velocity dispersion threshold (40km/s) above which NSCs should inevitably form a massive BH. To provide an observational test of these theories, we measure X-ray emission from NSCs and compare it to the measured velocity dispersion and tidal capture runaway timescale. We find that NSCs above the 40km/s threshold are X-ray detected at roughly twice the rate of those below (after accounting for contamination from X-ray binaries).