Session K01: Coalescence Rates of Compact Binary Systems

Live

Over the last 5 years, gravitational-wave astronomy has completely transformed our understanding of binary black hole astrophysics: in half a decade, we have gone from a purely theoretical field to a data-driven one, where \textbf{the majority of observed stellar-mass black holes have been observed by LIGO and Virgo}. But as impressive as this is, there is still much work to be done to understand how and where these binaries are formed. In this talk, I will review many of the theoretical models for binary black hole formation, with a particular emphasis on the merger rates they predict and how those rates change over cosmic time. I will argue that \textbf{ironically, the reduced uncertainty in the observed merger rate has complicated the theoretical landscape}, with many different formation scenarios now able to explain many, if not all, of the current binary black hole observations. Finally, I will connect these observations and their uncertainties to the greater cosmological context, and show how our theoretical understanding of black hole merger rates can be informed by our understanding of galaxy formation and evolution.   

Live

Mergers of binary systems of black holes and neutron stars are so far the only sources of detectable gravitational wave signals, with order(50) such events in the most recent cumulative catalog. With increasing detector sensitivity and number of signals, we are able to obtain relatively precise rate estimates for such sources, primarily binary black holes and neutron stars, as well as stronger limits on so far unobserved source types. For binary black holes, the most frequently observed signal type, we can also probe the differential merger rate, i.e. source distribution, over binary masses, spins and over redshift, offering several clues to possible formation channels. I will be surveying recent results on merger rates from the third Advanced LIGO-Virgo observing run (O3).   

Live

Neutron Star mergers are canonical multimessenger sources, observations of which enable unique insights into dense matter, fundamental physics, the origin of the elements, ultrarelativistic particle acceleration, and more. Their intrinsic rate in the local universe and its evolution through cosmic time inform on stellar evolution, the heavy (r-process) enrichment history, and determines how often we can expect them. The local rate can currently be directly measured from gravitational wave observations, with values currently based on 2 detections. The cosmic rate can also be determined from observations of short gamma-ray bursts, where we currently have a sample 2 to 3 orders of magnitude larger; however, these inferred rates are model-dependent. I will review the inferred rates prior to GRB 170817A, how what we learned from this event altered our expectations, and outline the science gained from measuring the local rate in different messengers.