Spin-orbit misalignment from triple-star common envelope evolution

TL;DR

This paper explores how triple star common envelope evolution can produce spin-orbit misalignments in compact binaries, potentially affecting gravitational wave sources and planetary nebulae formation.

Contribution

It introduces a new mechanism involving jets during triple star CEE that causes spin-orbit misalignment in resulting compact binaries.

Findings

CEE with inclined triples can tilt the envelope spin.

Misaligned jets can lead to spin-orbit misaligned BH/NS binaries.

Multiple scenarios predict different spin alignments in the remnants.

Abstract

I study a triple star common envelope evolution (CEE) of a tight binary system that is spiraling-in inside a giant envelope and launches jets that spin-up the envelope with an angular momentum component perpendicular to the orbital angular momentum of the triple star system. This occurs when the orbital plane of the tight binary system and that of the triple star system are inclined to each other, so the jets are not along the triple star orbital angular momentum. The merger of the tight binary stars also tilts the envelope spin direction. If the giant is a red supergiant (RSG) star that later collapses to form a black hole (BH) the BH final spin is misaligned with the orbital angular momentum. Therefore, CEE of neutron star (NS) or BH tight binaries with each other or with one main sequence star (MSS) inside the envelope of an RSG, where the jets power a common envelope jets supernova (CEJSN) event, might end with a NS/BH-NS/BH close binary system with spin-orbit misalignment. Such binaries can later merge to be gravitational waves sources. I list five triple star scenarios that might lead to spin-orbit misalignments of NS/BH-NS/BH binary systems, two of which predict that the two spins be parallel to each other. In the case of a tight binary system of two MSSs inside an asymptotic giant branch star the outcome is an additional non-spherical component to the mass loss with the formation of a messy planetary nebula.