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On the evolution of massive stellar triples

Stegmann, Jakob 2023. On the evolution of massive stellar triples. PhD Thesis, Cardiff University.
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Most massive stars are found in hierarchical triples or higher multiplicity systems, in which a close inner binary is orbited by one or more distant companions. Here, we present a new triple stellar evolution code, TSE, which simultaneously takes into account the physics of the stars and their gravitational interaction. TSE is used to simulate the evolution of massive stellar triples in the galactic field from the zero-age-main-sequence until they form compact objects. To this end, we implement initial conditions that incorporate the observed high correlation between the orbital parameters of early-type stars. We show that the interaction with a tertiary companion can significantly impact the evolution of the inner binary. For instance, high eccentricities can be induced by the third-body dynamical effects, leading to a Roche-lobe overflow or even to a stellar merger from initial inner binary separations of 10^3 to 10^5 solar radii. Focusing on the evolution subsequent to a stellar merger, we find that binaries composed of the merger product star and the tertiary companion provide a new source to form binary black hole mergers in the Galactic field. By means of a population synthesis, we estimate their contribution to the total black hole merger rate to be R(z=0)~0.3-25.2 per Gpc^3 and yr. Merging binary black holes that form from stellar post-merger binaries have exceptionally low mass ratios. We identify a critical mass ratio q~0.5 below which they could dominate the total black hole merger rate in the field. Lastly, we study the dynamical evolution of the spin vector of a massive donor star that stably transfers mass to a binary companion. Assuming that the donor star loses its mass along the instantaneous interstellar axis, we find that the ejection of $\gtrsim30$ per cent 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.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Uncontrolled Keywords: astrophysics, gravitational waves, massive stars, stellar triples, stellar evolution, stellar mergers, black holes
Funders: Cardiff University PSE College
Date of First Compliant Deposit: 1 August 2023
Last Modified: 10 Feb 2024 02:31

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