Evolution and final fate of massive post-common-envelope binaries

TL;DR

This study uses 3D simulations and stellar evolution models to investigate the evolution, final fate, and merger prospects of massive post-common-envelope binaries, highlighting the influence of circumbinary disks on their orbital dynamics.

Contribution

It introduces the role of circumbinary disks in post-CE binary evolution and demonstrates their impact on merger likelihood and orbital properties, which was not fully understood before.

Findings

Post-CE binaries are likely surrounded by massive circumbinary disks.

Mass accretion from disks can widen orbits, while resonant interactions can shrink them.

CBD interactions may increase the fraction of binaries merging via gravitational waves.

Abstract

Mergers of neutron stars (NSs) and black holes (BHs) are nowadays observed routinely thanks to gravitational-wave (GW) astronomy. In the isolated binary-evolution channel, a common-envelope (CE) phase of a red supergiant (RSG) and a compact object is crucial to sufficiently shrink the orbit and thereby enable a merger via GW emission. Here, we use the outcomes of two three-dimensional (3D) magneto-hydrodynamic CE simulations of an initially 10.0 solar-mass RSG with a 5.0 solar-mass BH and a 1.4 solar-mass NS, respectively, to explore the further evolution and final fate of the post-CE binaries. Notably, the 3D simulations reveal that the post-CE binaries are likely surrounded by circumbinary disks (CBDs), which contain substantial mass and angular momentum to influence the subsequent evolution. The binary systems in MESA modelling undergo another phase of mass transfer (MT) and we find that most donor stars do not explode in ultra-stripped supernovae (SNe), but rather in Type Ib/c SNe. The final orbits of our models with the BH companion are too wide, and NS kicks are actually required to sufficiently perturb the orbit and thus facilitate a merger via GW emission. Moreover, by exploring the influence of CBDs, we find that mass accretion from the disk widens the binary orbit, while CBD-binary resonant interactions can shrink the separation and increase the eccentricity depending on the disk mass and lifetime. Efficient resonant contractions may even enable a BH or NS to merge with the remnant He stars before a second SN explosion, which may be observed as gamma-ray burst-like transients, luminous fast blue optical transients and Thorne-\.Zytkow objects. For the surviving post-CE binaries, the CBD-binary interactions may significantly increase the GW-induced double compact merger fraction. We conclude that accounting for CBD may be crucial to better understand observed GW mergers.