"The formation of ultra-compact binaries in globular clusters through stable mass transfer, by Marc van der Sluys (Northwestern University)
The galactic globular clusters contain roughly a thousand times more X-ray binaries than the disc of the Galaxy. Many of the X-ray binaries in globular clusters have an ultra-short period (<~ 60 min). There were two theories to explain the formation of these systems, and the fact that many of them are ultra-compact: evolution from primordial binaries, or formation by direct collision. I will talk about the first scenario in detail, and finish with an update on our understanding today.