The formation of compact object binaries through isolated binary evolution

Neijssel, Coenraad Jacob (2022). The formation of compact object binaries through isolated binary evolution. University of Birmingham. Ph.D.

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Observations indicate that most stars are in binary or higher multiplicity systems (Preibisch et al., 1999; Sana et al., 2012, 2013; Duchêne and Kraus, 2013; Chini et al., 2013; Sota et al., 2014; Kobulnicky et al., 2014; Dunstall et al., 2015; Moe and Di Stefano, 2017; Sana, 2017). In a binary two stars orbit each other, bound by their mutual gravitational pull. If the orbital separation is short enough the stars interact, drastically altering their evolution. In the past decades, the means to perform complex calculations have drastically improved, giving us the chance to explore the physics of binary evolution in greater detail. This helped explain several observed properties, amongst others, why some stars are more luminous than expected or have peculiar surface abundances. Nonetheless, large uncertainties persist in the field of binary star physics.

In 2015, the gravitational waves from two colliding black holes were detected for the first time (Abbott et al., 2016b). For decades it has been hypothesised that two massive stars in an isolated binary could interact without external influences and form a binary black hole system tight enough to merge in a Hubble time (van den Heuvel and De Loore, 1973; Tutukov and Yungelson, 1973). In this dissertation I follow in the footsteps of many other studies and assume the observed gravitational-wave events come from isolated binary evolution, even though other formation channels for the mergers of neutron stars and black holes are also possible. The aim is to study what constraints, if any, properties of gravitational-wave events can place on the evolution of massive stars in binaries.

The general approach in of this dissertation is to evolve a population of stars under various model assumptions and estimate the rates and properties of gravitational wave mergers for each model. The predicted distributions enable a quantitative or qualitative assessment of the impact of current uncertainties in binary-star physics on estimates of the rates and masses of gravitational-wave events. Evaluating the effect of uncertainties is crucial to determine whether comparisons between synthetic populations of gravitational-wave sources and observations can place meaningful constraints on binary-star physics. If the uncertainties are large and model-dependent features are not predicted, then the detections of gravitational-wave mergers may only provide marginal constraints.

In this dissertation I assess the impact of the following model assumptions. In chapter 4 I investigate the uncertainties in the rate and initial chemical composition with which stars form and the impact of these uncertainties on the predictions of the merger rate of neutron stars and black holes. In chapter 5 I vary the response of stars to mass loss and explore how it alters the interactions that lead to the formation of binary black holes. In chapter 6 I examine whether Cygnus X-1 may evolve into a binary black hole system and if the observed mass of the black hole in Cygnus X-1 provides constraints on the wind mass-loss rates of stars. Chapter 1 and chapter 2 provide introductory material for the reader on stellar evolution and binary interactions. Chapter 3 summarises the theoretical model used in this dissertation to evolve a population of stars. Chapter 7 provides a summary and personal view on the conclusions of this dissertation.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Licence: All rights reserved
College/Faculty: Colleges (2008 onwards) > College of Engineering & Physical Sciences
School or Department: School of Physics and Astronomy
Funders: None/not applicable
Subjects: Q Science > QC Physics


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