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Flipping spins in mass transferring binaries and origin of spin-orbit misalignment in binary black holes

Stegmann, Jakob and Antonini, Fabio ORCID: https://orcid.org/0000-0003-3138-6199 2021. Flipping spins in mass transferring binaries and origin of spin-orbit misalignment in binary black holes. Physical Review D 103 , 063007. 10.1103/PhysRevD.103.063007

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Abstract

Close stellar binaries are prone to undergo a phase of stable mass transfer in which a star loses mass to its companion. Assuming that the donor star loses mass along the instantaneous interstellar axis, we derive the orbit-averaged equations of motion describing the evolution of the donor rotational angular momentum vector (spin) that accompanies the transfer of mass. We consider: (i) a model in which the mass transfer rate is constant within each orbit and (ii) a phase-dependent rate in which all mass per orbit is lost at periapsis. In both cases, we find that the ejection of ≳ 30 percent of the donor’s initial mass causes its spin to nearly flip onto the orbital plane of the binary, independently of the initial spin-orbit alignment. Moreover, we show that the spin flip due to mass transfer can easily dominate over tidal synchronization in any giant stars and main-sequence stars with masses ∼ 1.5 to 5     M ⊙ . Finally, the general equations of motion, including tides, are used to evolve a realistic population of massive binary stars, leading to the formation of binary black holes. Assuming that the stellar core and envelope are fully coupled, the resulting tilt of the first-born black hole reduces its spin projection onto the orbit normal by a factor ∼ O ( 0.1 ) . This result supports previous studies in favor of an insignificant contribution to the effective spin projection, χ eff , in binary black holes formed from the evolution of field binaries.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: American Physical Society
ISSN: 2470-0010
Date of First Compliant Deposit: 4 February 2021
Date of Acceptance: 1 February 2021
Last Modified: 09 Nov 2022 10:06
URI: https://orca.cardiff.ac.uk/id/eprint/138273

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