Potential PhD projects: Extragalactic Astrophysics and Cosmology

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)

Project: Galaxy formation with the next generation of telescopes

Supervisor: Dr Sean McGee

During this PhD, the next generation of telescopes and surveys used to study galaxy formation will become available. This includes new observatories like Large Synoptic Survey Telescope, the Euclid space telescope, and the James Webb Space Telescope as well as new instruments like WEAVE on the William Herschel Telescope and MOONS on the Very Large Telescopes. This PhD will prepare and make use of these new tools to examine galaxy formation. 

There are several possible projects including, but not limited to: the tidal disruption of stars by the black holes in galaxies and their subsequent effect on the galaxy hosts; the effect of environment on the formation of galaxies through cosmic time; and constraining the mass function of dark matter halos with strong gravitational lensing.

For more information, please email Dr. Sean McGee (smcgee[at]star.sr.bham.ac.uk)

Project:Gravitationally lensed explosive transients

Supervisor: Dr Graham Smith

Gravitationally lensed explosive transients is an exciting and rapidly growing field, fuelled by the first discovery of a multiply-imaged supernova, the first direct detection of gravitational waves, and the upcoming Vera Rubin Observatory (Rubin). The basic idea is that the flux of radiation from some high energy events (e.g. supernovae, gamma ray bursts, and mergers of compact objects) in the distant universe is magnified and even split in to several images of the same event by the gravitational lensing effect of a massive galaxy or cluster of galaxies that the radiation encounters enroute to our telescopes and detectors on Earth.

Detection and detailed study of this phenomenon probe a wide range of fundamental physics including tests of general relativity, the nature of dark matter, the expansion history of the universe, and the physics of explosive transients and their progenitors in the distant universe. In Birmingham we are at the forefront of research in to gravitationally lensed gravitational waves and their optical counterparts, and the role that galaxy clusters play in the broader field of gravitationally lensed explosive transients. We are pursuing this research within the framework of Rubin’s Strong Lensing Science Collaboration, and the LSST:UK Consortium, for which Dr Smith is currently co-Chair and Commissioning Scientist respectively.

A PhD in Birmingham would see students joining these organisations and thus having Rubin data rights, and collaborating with us and our international colleagues on this cutting edge research. Projects can be constructed to suit students' strengths and interests, and for example can focus on analysis of observational data aiming to make ground-breaking discoveries, and/or modelling and interpretation of discoveries to learn new physics. To get a flavour of our work and the opportunities available to a new student, please take a look at these papers/links:

Discovering gravitationally lensed gravitational waves: predicted rates, candidate selection, and localization with the Vera Rubin Observatory

On the gravitational lensing interpretation of three gravitational wave detections in the mass gap by LIGO and Virgo

Enabling discovery of gravitationally lensed explosive transients: a new method to build an all-sky watch-list of groups and clusters of galaxies

Strong Lensing Science Collaboration input to the on-sky commissioning of the Vera Rubin Observatory

What does strong gravitational lensing? The mass and redshift distribution of high-magnification lenses

On building a cluster watchlist for identifying strongly lensed supernovae, gravitational waves and kilonovae

Deep and rapid observations of strong-lensing galaxy clusters within the sky localization of GW170814

What if LIGO's gravitational wave detections are strongly lensed by massive galaxy clusters?

For more information, please email Dr Graham Smith (gps[at]star.sr.bham.ac.uk)