Binary neutron star formation (IMAGE) University of California - Santa Cruz Caption In the late stages of binary neutron star formation, the giant star expands and engulfs the neutron star companion in a stage referred to as common-envelope evolution (a). Ejection of the envelope leaves the neutron star in a close orbit with a stripped-envelope star. The evolution of the system depends on the mass ratio. Less-massive stripped stars experience an additional mass transfer phase that further strips the star and recycles the pulsar companion, leading to systems such as the observed binary neutron stars in the Milky Way and GW170817 (b). More massive stripped stars do not expand as much, therefore avoiding further stripping and companion recycling, leading to systems such as GW190425 (c). Finally, even more massive stripped stars with will lead to black hole-neutron star binaries such as GW200115 (d). Credit (Image credit: Vigna-Gomez et al., ApJL 2021) Usage Restrictions For use only with news coverage of this research License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.