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You spin me round: Measuring precession in the black hole population

Hoy, Charlie G. 2021. You spin me round: Measuring precession in the black hole population. PhD Thesis, Cardiff University.
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Black holes: cosmic bodies of extreme gravity that nothing, not even light, can escape. Einstein first told the world about the existence of these enigmatic objects in his groundbreaking theory of General Relativity. It was not until 2015 that black holes were probed directly through the first observation of gravitational waves. The treasure trove of knowledge gleaned from this observation revolutionised our understanding of the cosmos. Since this Nobel prize winning observation, the LIGO Scientific, Virgo and KAGRA collaborations have observed fifty gravitational waves. The aim of this thesis has been to take advantage of the growing population of gravitational wave sources to answer the following fundamental question: do binary black holes undergo spin-induced orbital precession? This has significant implications on our understanding of how binary black holes form in nature. To answer this question, I first introduced a brand new formalisation for modelling a gravitational wave that originated from a precessing system. I then introduced the 'precession signal-to-noise ratio' which naturally followed from this unique description. This novel tool quantified, for the first time, the significance of precession in an observed gravitational wave. I then used the 'precession signal-to-noise ratio' to demonstrate a) that there is no evidence for precession in any of the binary black hole candidates from the first gravitational wave catalog and b) how this lack of precession allows us to constrain the properties of black holes. I then presented the properties of potentially the first neutron star-black hole binary observed -- a system which is most likely to have measurable precession as a result of the asymmetric component masses. I then calculated the 'precession signal-to-noise ratio' for all gravitational wave candidates observed in the first half of the third gravitational wave observing run, and demonstrated that three observed gravitational waves could have originated from precessing systems. I then used the gravitational wave data from the second gravitational wave catalog to determine the most likely spin distribution of black holes. By doing so, I was able to determine whether the population of binary black holes are likely to undergo spin-induced orbital precession. Finally, I presented a new and innovative software package to analyse, display and combine posterior samples. This package has become one of the major workhorses of the LIGO Scientific, Virgo and KAGRA collaborations and is widely distributed through the gravitational wave data analysis computing environment.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Uncontrolled Keywords: Keywords: gravitational waves; black hole binaries; precession; bayesian inference; software; python
Funders: STFC, Cardiff University, School of Physics and Astronomy
Date of First Compliant Deposit: 1 July 2021
Last Modified: 01 Jul 2021 14:56

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