Novel effects in field accretion around black holes

Thesis

Black holes are some of the most mysterious and fascinating objects in the Uni- verse. Due to the environments of extreme spacetime curvature they produce, for a theoretical physicist, they can serve as useful laboratories where interesting phenomena associated with various physical fields and functions can be manifest and therefore studied. In this thesis, I am particularly concerned with the effects which appear during the accretion of various beyond-standard model fields onto black holes, and how these effects vary depending on the microphysics of the particle in question.

Firstly, I consider two distinct models of scalar field. The first model involves an additional quartic term to the potential of the particle, coupled with a parameter λ. I study the accretion of clouds of these particles onto isolated Schwarzschild black holes, and how different values of λ affects the behaviour and growth of these fields as they accrete. I then consider the effects that these fields have on the merger of binary black holes, both on the cloud itself, and on the merger dynamics itself.

The second category of scalar fields I investigate are multi-minima models, in order to study the phenomena of symmetry restoration and vacuum decay. These are effects reliant on the field beginning at an energy scale where it oscillates around a single one of the potential minima. I am focused on how black hole accretion can increase the energy of the field, and so catalyse a phase transition in the field, undergoing a change from one state to another as it begins to explore regions of the potential outside of its initial minimum.

In my final chapter, I introduce formalism for simulating massive rank-2 tensor fields in 3+1 numerical relativity. I start from the general action, and then split up the field into a series of constituent sub-fields. By defining a new tensor related to the first derivative of the field, I substitute this in to the wave equation and undergo a series of derivations to find a set of evolution equations for the aforementioned sub-fields and their associated conjugate momenta. I then demonstrate some example simulations one can perform with these equations, including the scattering of gravitational waves around a black hole, before detailing ideas for future work on this project.

Authors: Marsden, J

• DOI: 10.5287/ora-damnp5mek
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: black holes; general relativity; gravitational waves; wave dark matter; numerical relativity; early universe
• Subjects: Multigrid methods (Numerical analysis); General relativity (Physics); Dark matter (Astronomy); Gravitational waves; Black holes (Astronomy); Computer simulation; Broken symmetry (Physics)