Rapid population synthesis of black-hole high-mass X-ray binaries: implications for binary stellar evolution

Abstract

We conduct binary population synthesis to investigate the formation of wind-fed high-mass X-ray binaries containing black holes (BH-HMXBs). We evolve multiple populations of high-mass binary stars and consider BH-HMXB formation rates, masses, spins and separations. We find that systems similar to Cygnus X-1 likely form after stable Case A mass transfer (MT) from the main sequence progenitors of black holes, provided such MT is characterised by low accretion efficiency, $\beta \lesssim 0.1$, with modest orbital angular momentum losses from the non-accreted material. Additionally, efficient BH-HMXB formation relies on a new simple treatment for Case A MT that allows donors to retain larger core masses compared to traditional rapid population-synthesis assumptions. At solar metallicity, our Preferred model yields $\mathcal{O}(1)$ observable BH-HMXBs in the Galaxy today, consistent with observations. In this simulation, $8\%$ of BH-HMXBs go on to merge as binary black holes or neutron star-black hole binaries within a Hubble time; however, none of the merging binaries have BH-HMXB progenitors with properties similar to Cygnus X-1. With our preferred settings for core mass growth, mass transfer efficiency and angular momentum loss, accounting for an evolving metallicity, and integrating over the metallicity-specific star formation history of the Universe, we find that BH-HMXBs may have contributed $\approx2$--$5$ BBH merger signals to detections reported in the third gravitational-wave transient catalogue of the LIGO-Virgo-KAGRA Collaboration. We also suggest MT efficiency should be higher during stable Case B MT than during Case A MT.