Prof. Bernard F. Schutz

LIGO's landmark first detection in 2015 already told us to expect that binary black holes are heavier and more numerous than we had anticipated. But now, after three observing runs, LIGO and Virgo have begun to reveal a fascinating variety of compact binary systems: binary neutron stars, binaries with components that have masses that “shouldn't” exist, binaries with big mass ratios, binaries that might have formed from triple systems and others that might have had active galaxies as nursemaids, and more. The connections between GW astronomy and other parts of astronomy are becoming clearer, and more numerous. Currently the detectors are undergoing an upgra de, which has been slowed by the COVID-19 pandemic. When they begin their fourth observing run in mid-2022, we will be anticipating more exotica but also much larger numbers of events (often more than one per day) and consequently better statistics. And when the A+ upgrade becomes operational, and LIGO-India joins the network, the surprises will certainly continue!