ASTROMETRIC BINARIES WITH DARK COMPANIONS IN THE GLOBULAR CLUSTER OMEGA CENTAURI - JOHANNES SAHLMANN

We present the discovery of the first astrometric binaries in the globular cluster omega Centauri. This was made possible by analysing 13 years of regularly-scheduled Hubble Space Telescope calibration observations in the cluster core. We determined the astrometric orbits of four binaries and their Keplerian parameters suggest periods of 9-19+ years and dark companions in the mass range of 0.7-1.4 solar masses, including at least one neutron-star candidate. We discuss the potential of astrometric binary searches in globular clusters in the context of the recent Gaia Focused Product Release and future Gaia data releases.