We discovered a population of black hole X-ray binaries (XRBs) in the merging Antennae galaxies. We have developed a new methodology (utilizing X-ray and optical data plus N-body simulations) to study the nature of XRBs in nearby galaxies. You can read the full paper here or read the abstract below.
We compare the locations of 82 XRBs detected in the merging Antennae galaxies by Zezas et al., based on observations taken with the Chandra X-Ray Observatory, with a catalog of optically selected star clusters presented by Whitmore et al., based on observations taken with the Hubble Space Telescope.