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Abstract The formation histories of compact binary mergers, especially stellar-mass binary black hole mergers, have recently come under increased scrutiny and revision. We revisit the question of the dominant formation channel and efficiency of forming binary neutron star (BNS) mergers. We use the stellar and binary evolution codeMESAand implement a detailed method for common envelope and mass transfer. We perform simulations for donor masses between 7 M⊙and 20 M⊙with a neutron star (NS) companion of 1.4 M⊙and 2.0 M⊙ at two metallicities, using varying common envelope efficiencies and two different prescriptions to determine if the donor undergoes core collapse or electron capture, given their helium and carbon–oxygen cores. In contrast to the case of binary black hole mergers, for an NS companion of 1.4 M⊙, all BNS mergers are formed following a common envelope phase. For an NS mass of 2.0 M⊙, we identify a small subset of mergers following only stable mass transfer if the NS receives a natal kick sampled from a Maxwellian distribution with velocity dispersionσ= 265 km s−1. Regardless of the supernova prescription, we find more BNS mergers at subsolar metallicity compared to solar.
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This content will become publicly available on September 5, 2026
Rapid Binary Mass Transfer: Circumbinary Outflows and Angular Momentum Losses
High rates of stable mass transfer likely occur for some binary star systems, but the resulting flow of mass and angular momentum (AM) is unclear. We perform hydrodynamical simulations of a polytropic donor star and a point-mass secondary to determine the mass, AM, and velocity of gas that leaves the system, and the dependence on binary parameters such as mass ratio. The simulations use an adiabatic equation of state and do not include radiative cooling or irradiation of the outflow. Mass transfer is initiated by injecting heat into the stellar envelope, causing it to gradually inflate and overflow its Roche lobe. The transferred mass flows into an accretion disk, but soon begins to escape through the outer Lagrange point (L2), with a lesser amount escaping through the L3 point. This creates an equatorially concentrated circumbinary outflow with an opening angle of 10°–30° with a wind-like density profileρ∝r−2. We find that the ratios of the specific AM of the outflowing gas over that of the L2 point are approximately {0.95, 0.9, 0.8, 0.65} for mass ratiosq= {0.25, 0.5, 1, 2} (accretor/donor). The asymptotic radial velocity of the outflowing gas, in units of the binary orbital velocity, is approximately 0.1–0.2 for the same mass ratios, except forq= 0.25, where it might be higher. This outflow, if ultimately unbound from the binary, may be a source of circumstellar material that interacts with ejecta from a subsequent supernova or stellar merger.
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- Award ID(s):
- 2205974
- PAR ID:
- 10654584
- Publisher / Repository:
- The Astrophysical Journal
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 990
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 172
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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