Published on Wed Jun 23 2021
Fallback Supernova Assembly of Heavy Binary Neutron Stars and Light Black Hole–Neutron Star Pairs and the Common Stellar Ancestry of GW190425 and GW200115
The detection of the unusually heavy binary neutron star merger GW190425
marked a stark contrast to the mass distribution from known Galactic
millisecond pulsars in neutron star binaries and gravitational-wave source
GW170817. We suggest here a formation channel for heavy binary neutron stars in
which massive helium stars, assembled after common envelope, remain compact and
avoid mass transfer onto the neutron star companion and thus evade pulsar
recycling. In particular we present three-dimensional simulations of the
supernova explosion of the massive stripped helium star and follow the mass
fallback evolution and the subsequent accretion onto the neutron star
companion. We find that fallback leads to significant mass growth in the newly
formed neutron star and that the companion does not accrete sufficient mass to
become a millisecond pulsar. This can explain the formation of heavy binary
neutron star systems such as GW190425, as well as predict the assembly of
neutron star - light black hole systems. Moreover, this hints to the existence
of a sizable population of radio-quiet double compact objects in our Galaxy.
Finally, this formation avenue is consistent with the observed
mass-eccentricity correlation of binary neutron stars in the Milky Way.