Implications of Modern Mass-loss Rates for Massive Stars

Abstract Massive stars lose a significant fraction of their mass through stellar winds at various stages of their lives, including on the main sequence, during the red supergiant (RSG) phase, and as helium-rich stripped stars. In stellar population synthesis, uncertainty in the mass-loss rates in these evolutionary stages limits our understanding of the formation of black holes and merging compact binaries. In the last decade, the theoretical predictions, simulation, and direct observation of wind mass-loss rates in massive stars have improved significantly, typically leading to a reduction in the predicted mass-loss rates of massive stars. In this paper we explore the astrophysical implications of an updated treatment of winds in the COMPAS population synthesis code. There is a large amount of variation in predicted mass-loss rates for massive RSGs; some of the prescriptions we implement predict that massive RSGs are able to lose their hydrogen envelopes through winds alone (providing a possible solution to the so-called missing RSG problem), while others predict much lower mass-loss rates that would not strip the hydrogen envelope. We discuss the formation of the most massive stellar-mass black holes in the Galaxy, including the high-mass X-ray binary Cygnus X-1 and the newly discovered Gaia BH 3. We find that formation rates of merging binary black holes are sensitive to the mass-loss rate prescriptions, while the formation rates of merging binary neutron stars and neutron-star black hole binaries are more robust to this uncertainty.