Black-hole Ringdown: Quasinormal Modes in Numerical-relativity Simulations and Gravitational-wave Observations

Finch, Eliot ORCID: 0000-0002-1993-4263 (2023). Black-hole Ringdown: Quasinormal Modes in Numerical-relativity Simulations and Gravitational-wave Observations. University of Birmingham. Ph.D.

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Abstract

The study of black-hole ringdown, the endpoint of a binary black-hole merger, is a cornerstone of gravitational-wave astronomy. A black hole's characteristic quasinormal-mode spectrum offers the possibility of clean and powerful tests of general relativity, encoding the properties of the remnant black hole (and, in principle, the binary from which it was formed) in the superposition of exponentially-damped sinusoids which constitute the ringdown signal. The observation of gravitational-wave signals is now routine, and the burgeoning field of black-hole spectroscopy is already contributing to our knowledge of the gravitational-wave sky.

In this thesis we investigate the ringdown in two ways. Firstly, we develop our ringdown models by performing fits directly to state-of-the-art numerical-relativity simulations. Our analysis considers, for the first time, a large selection of black-hole binaries with misaligned spins. In this clean and noise-free regime we can understand which quasinormal modes are important to include in our models, and it also informs us on the choice of ringdown start time. These studies help to guide our expectations when we analyse real gravitational-wave data. Secondly, we develop a novel frequency-domain ringdown analysis method for use with real data, applying it to both simulated signals and to real gravitational-wave data. Our method solves many of the problems associated with conventional ringdown-only analyses. Applying the method to GW150914, we quantify the significance with which a ringdown overtone can be found in the data.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):