From spherical stars to disk-like structures: 3D common-envelope evolution of massive binaries beyond inspiral

¹ Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr, 12–14 69120 Heidelberg, Germany
² Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Philosophenweg 12, 69120 Heidelberg, Germany
³ Heidelberger Institut für Theoretische Studien, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg, Germany
⁴ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching, Germany
⁵ Max Planck Computing and Data Facility, Gießenbachstraße 2, 85748 Garching, Germany

^⋆ Corresponding author; marco.vetter@stud.uni-heidelberg.de

Received: 19 July 2024
Accepted: 3 October 2024

Abstract

Self-consistent three-dimensional modeling of the entire common-envelope phase of gravitational wave progenitor systems until full envelope ejection is challenged by the vast range of spatial and temporal scales involved in the problem. Previous attempts were either terminated shortly after the rapid spiral-in with significant amounts of gravitationally bound material left in the system or they omitted this plunge-in phase and modeled the system afterward. We investigated the common-envelope interactions of a 10 M_⊙ red supergiant primary star with a black hole and a neutron star companion, respectively, until full envelope ejection (≳97% of the envelope mass). In contrast to the expectation from e.g. population synthesis models, we find that the dynamical plunge-in of the systems determines (to leading order) the orbital separations of the core binary system, while the envelope ejection by recombination acts only at later stages of the evolution and fails to harden the core binaries down to orbital frequencies where they qualify as progenitors of gravitational-wave-emitting double-compact object mergers. Diverging from the conventional picture of an expanding common envelope that is ejected more or less spherically, our simulations show a new mechanism: The rapid plunge-in of the companion transforms the spherical morphology of the giant primary star into a disk-like structure. During this process, magnetic fields are amplified, and the subsequent transport of material through the disk around the core binary system drives a fast jet-like outflow in the polar directions. While most of the envelope material is lost through a recombination-driven wind from the outer edge of the disk, about 7% of the envelope leaves the system via the magnetically driven outflows. We further explored the potential evolutionary pathways of the post-common-envelope systems in light of the expected remaining lifetime of the primary core (2.97 M_⊙) until core collapse (6 × 10⁴ yr), most likely forming a neutron star. We find that the interaction of the core binary system with the circumbinary disk substantially increases the likelihood of giving rise to a double-neutron star merger (55%) or a neutron star black hole (5%) merger event.