Stable case BB/BC mass transfer to form GW190425-like massive binary neutron star mergers

Abstract

On April 25, 2019, the LIGO-Virgo Collaboration discovered a gravitational-wave (GW) signal from a binary neutron star (BNS) merger, that is, GW190425. Due to the inferred large total mass, the origin of GW190425 remains unclear. Assuming GW190425 originated from the standard isolated binary evolution channel, its immediate progenitor is considered to be a close binary system, consisting of a He-rich star and a NS just after the common envelope phase. We aim to study the formation of GW190425 in a solar-like environment by using the detailed binary evolution code MESA We perform detailed stellar structure and binary evolution calculations that take into account mass loss, internal differential rotation, and tidal interactions between a He-rich star and a NS companion. We explore the parameter space of the initial binary properties, including initial NS and He-rich masses and initial orbital period. We find that the immediate post-common-envelope progenitor system, consisting of a primary $ NS and a secondary He-rich star with an initial mass of $ in a close binary with an initial period of $ days days $), that experiences stable Case BB/BC mass transfer (MT) during binary evolution, can reproduce the formation of GW190425-like BNS events. Our studies reveal that the secondary He-rich star of the GW190425's progenitor before its core collapse can be efficiently spun up through tidal interaction, finally remaining as a NS with rotational energy even reaching $ erg $, which is always much higher than the neutrino-driven energy of the supernova (SN) explosion. If the newborn secondary NS is a magnetar, we expect that GW190425 can be the remnant of a magnetar-driven SN, namely a magnetar-driven ultra-stripped SN, a superluminous SN, or a broad-line Type Ic SN. Our results show that GW190425 could be formed through the isolated binary evolution, which involves a stable Case BB/BC MT just after the common envelope phase. On top of that, we show the He-rich star can be tidally spun up, potentially forming a spinning magnetized NS (magnetar) during the second SN explosion.