Potential PhD projects: Gravitational Wave Astrophysics

Project: Tidal disruptions of stars by supermassive black holes

Supervisor: Dr Clément Bonnerot

When a star wanders too close to a supermassive black hole, it gets torn apart by extreme gravitational forces, leading to a powerful flash of light detectable from billions of light years (see here for a recent example).

While most of these black holes lie undetectable in the centers of galaxies, such tidal disruption events represent unique probes to shed light on these gargantuan objects and the extreme processes happening in their vicinity. Starting next year, this research field will be revolutionized by the Rubin Observatory , which is expected to discover several thousands of new events throughout the Universe.

The main goal of this PhD project is to build a robust theoretical framework that can be used to optimally interpret the emission received from tidal disruption events at the dawn of this observational golden era. This work will involve both pen-and-paper calculations and simulations carried out on supercomputers to reach an understanding of the complex gas dynamics at play when a star gets destroyed by a black hole, and to determine the resulting emission that observers can detect.

Depending on interests, this project can also be extended to different aspects of tidal disruption events or the study of other high-energy systems, particularly those leading to the emission of gravitational waves.

For more information, please do not hesitate to email Dr Clément Bonnerot (clement.bonnerot[at]gmail.com).

Project: Gamma-ray bursts and gravitational waves

Supervisor: Dr Ben Gompertz

Gamma-ray bursts are the most powerful explosive events in the universe, releasing as much energy in 10 seconds as the entire Milky Way galaxy does in several years. They are associated with either the collapse of very massive stars (long gamma-ray bursts) or collisions between two neutron stars or a neutron star and a black hole (short gamma-ray bursts). Because of this, gamma-ray bursts can tell us about some of the most extreme environments in nature, and are confirmed counterparts to gravitational-wave sources.

During this PhD, students will have the opportunity to research the systems that produce gamma-ray bursts, the environments they explode into, their connection to the creation of the heaviest elements in the universe, and their ability to probe gravitational-wave sources. An interested student will be able to join international collaborations like GOTO, LSST, STARGATE, and ENGRAVE, and gain access to some of the most powerful telescopes and satellite observatories in the world.

For more information, please email Dr. Ben Gompertz (bgompertz[at]star.sr.bham.ac.uk)

Gravitational Wave Astronomy

Supervisor: Dr Christopher J. Moore (Email cmoore[at]star.sr.bham.ac.uk)

The era of gravitational wave astronomy has begun. LIGO and Virgo have unearthed the signals from several pairs of merging black holes and one pair of merging neutron stars. Many more events are expected over the next few years. These signals must be compared against detailed theoretical models to enable us to accurately determine the properties of the sources. These theoretical models will need to be significantly improved to cope with the exquisite, high signal to noise ratio , observations promised by the next generation of ground-based detectors, as well as the upcoming space-based detector, LISA. This new generation of gravitational wave instruments will pose new challenges that must be overcome in order to maximise their scientific potential. These challenges include, for example, managing very long duration signals containing many more wave cycles, avoiding confusion when analysing data sets containing multiple simultaneous overlapping signals, and efficiently combining the information from the large numbers of events to learn about the underlying astrophysical processes. This project will aim to tackle some of these future challenges whilst also working with the current LIGO and Virgo observational data.

Compact Binaries

Supervisor: Dr Geraint Pratten (Email gpratten[at]star.sr.bham.ac.uk)

Compact binaries, consisting of pairs of black holes or neutron stars, are extremely powerful sources of gravitational radiation. Vital information on the physics that drives the coalescence of these binaries is directly encoded in the gravitational-wave signal. By decoding this information, we can obtain crucial knowledge on the origin and evolution of astrophysical black holes and neutron stars throughout the Universe. Our ability to extract this information requires developing new and increasingly sophisticated theoretical models for the gravitational-wave signal. This PhD project will aim to tackle key questions in gravitational-wave astronomy and fundamental physics. Research topics include: the analytical modelling of gravitational dynamics and radiation, numerical relativity simulations of compact binaries, acceleration techniques for gravitational-wave data analysis, testing fundamental physics in the strong-field regime, modelling neutron star mergers, and exploring our understanding of the neutron star equation of state.

The PhD Student will be strongly encouraged to join the LIGO Scientific Collaboration and be given the opportunity to work directly with gravitational-wave data and to play a role in the gravitational-wave discoveries made by the LIGO detector

Studying the physics and populations of black holes and neutron stars wi th gravitational-wave observations

Supervisor: Prof Alberto Vecchio (Email: av[at]star.sr.bham.ac.uk)

Projects are available to use LIGO/Virgo data to characterise the properties of black holes and neutron stars in binary systems, and the behaviour of extreme space-times. The gravitational-wave instruments LIGO and Virgo will re-start observations at improve sensitivity at the end of 2022 and are expected to observe hundreds of binary systems of black holes and neutron stars over the next few years. The project will focus on characterising the physical properties of the individual systems and, from those, the properties of the underlying populations. For selected systems, it may also be possible to use the gravitational-wave data to test specific predictions of general relativity.

Tackling the global analysis challenge of the Laser Interferometer Space Antenna

Supervisor: Prof Alberto Vecchio (Email: av[at]star.sr.bham.ac.uk)

ESA's Laser Interferometer Space Antenna (LISA) is going to be the first gravitational-wave observatory opening the mHz observational window onto the universe. LISA will discover tens of thousands of compact objects, from sub-solar mass white dwarfs in our galaxy to massive black holes at the centre of galaxies throughout the Universe. Projects are available to develop data analysis capabilities to maximise the science exploitation of this unique mission, using a combination of machine learning/AI techniques and (hierarchical) Bayesian inference tools.