PhD projects for Astrophysics studies starting in 2024

This is our current list of possible PhD projects for 2024. If your favourite topic is not in the list, we highly encourage you to contact staff in your fields of interest to discuss PhD projects.

The nature and origin of galactic structure in high resolution simulations

Supervisor: Robert Grand

Please note:
This project is only available for in-person students, not for distance learning students.

Most of the visible starlight in the Universe emanates from spiral galaxies like the Milky Way. A key goal of modern astrophysics is to understand their formation and evolution. Fortunately, the distribution, motions, and chemical compositions of their stellar populations hold vital memory of the Galactic evolutionary history from the very early Universe shortly after the Big Bang down to the present day, presenting a window into their past.

Recent observations from ESA’s Gaia mission and others have revolutionised how we see the Milky Way, garnering several exciting discoveries including an incredibly complex and rich “out-of-equilibrium” dynamical structure. Although much of this structure was completely unexpected, it has likely been shaped by a wide range of physical phenomena, such as the galactic bar and spiral arms, mergers, dark matter, and black holes.

Numerical simulations are some of the most powerful theoretical tools we have at our disposal to progress our understanding: they are necessary to provide crucial interpretation of observations, which are after all just a snapshot in time. The student will work with a new state-of-the-art suite of cosmological, magneto-hydrodynamical simulations of Milky Way-type galaxies. Through a combination of analysis and comparison to observations, these simulations will deliver new capabilities to address many open questions on galaxy formation and Galactic dynamics, including but not limited to:

  1. The nature and origin of galactic spiral arms: Spiral arms are iconic structures and significantly affect galaxy evolution, however their nature and origin are still unknown. Some open questions are: how and when did they form? how have they moved stars like the Sun around the Galaxy over billions of years? We will make new predictions from chemo-dynamics of disc stars to compare with observations.
  2. The Milky Way (and galaxies like it) have experienced numerous mergers and fly-by interactions with other galaxies in the past, which imprint chemo-dynamical signatures in the disc. The student will look for novel signatures of these events in order to put new constraints on the most recent and significant interactions and mergers.

There will also be opportunities for the student to develop and run simulations with the state-of-the-art Arepo simulation code.

Searching for tidal stellar streams in the Milky Way using methods based on cosmological simulations

Supervisors: Andreea Font, Robert Grand

Please note:
This project is available for both in-person and distance learning students (full-time or part-time).

Galaxies like the Milky Way form by accreting and disrupting many dwarf galaxies over their lifetime. Dwarf satellite galaxies which are tidally ripped apart by the gravitational field of the Milky Way leave behind tell-tale signatures in the form of stellar streams. From the number and shapes of these streams, we can reconstruct the merger history of our Galaxy, and constrain the 'mass function' of Galactic progenitors.

Observations in the Milky Way and other Milky Way analogues (such as Andromeda Galaxy) have revealed many of these tidal streams. However, many more streams are thought to remain still unidentified, given the difficulty of disentangling stream properties from the rest of the stellar halo.

Cosmological simulations of Milky Way-type galaxies can be used to improve the detection of these streams since these features can be traced accurately given the information available in the simulated data. In this project, we will use a large set of Milky Way-mass systems from Auriga and Artemis simulations, to improve the current methods of stream detection and make the connection between the current stream properties and the mass function of progenitors.

These methods will be then applied to current observations (e.g. data from Gaia space satellite, or from DESI), and to make predictions for future Galactic surveys (e.g., for GaiaNIR, which has recently been selected by ESA as a candidate for a large mission in the upcoming Voyage 2050 programme).

Galaxies in the first billion years of cosmic time

Supervisor: Renske Smit

Please note:
This project is only available for in-person students, not for distance learning students.

Our understanding of the formation of the first stars, the first galaxies, the first black holes, the first heavy elements and dust particles in the Universe is rapidly changing with revolutionary observational facilities such as the James Webb Space Telescope (JWST) and the Atacama Large Millimetre Array (ALMA).

In this PhD project we will look 13 billion year back in time and measure the physical properties of the first generations of galaxies in order to understand how early galaxy formation takes place. We will focus mainly on the rich data-sets that have been released in the first Cycle of JWST observations (looking at the stars and hot gas within galaxies), complemented at much longer wavelengths by ALMA (looking at the cold gas and dust).

Galaxy demographics

Supervisor: Ivan Baldry

Please note:
This project is available for both in-person (full-time) and distance learning students (part-time).

We can analyse galaxies individually or as a population. Focusing on the latter allows us to empirically track galaxy evolution since, if we measure demographics of galaxy populations at different distances, we are viewing the universe at different epochs. Measurements of galaxy populations can also be compared with cosmological-scale simulations. Galaxy demographics are therefore key for empirically describing and understanding galaxy evolution, and can also play a role in constraining cosmological models.

Some of the key demographic measurements are: the galaxy stellar mass function (distribution of galaxy masses), size-mass relation, colour-mass relation,
morphological and dynamical distributions. Related to this are measurements of the properties of the large-scale structure that the galaxies' inhabit: local environment, galaxy groups and clusters. These types of measurements place constraints on the processes affecting galaxy evolution and cosmological-scale
Models.

Various projects are available in this area, from finding and characterising the lowest-mass galaxies to testing the role of environment on galaxy evolution. The data are from photometric and spectroscopic surveys of galaxies.

Near field cosmology: the genesis of the Milky Way Galaxy and its dwarf satellites

Supervisor: Ricardo Schiavon

Please note:
This project is only available for in-person students, not for distance learning students.

This project aims at understanding how the Milky Way Galaxy was formed. The student will join the efforts of our team to analyse data from various cutting-edge surveys of Milky Way stars, including Gaia, APOGEE and WEAVE, in order to determine the distances, velocities, and chemical compositions of an unprecedented sample of over one million stars, and establish the history of our Galaxy. Specifically, the student will explore the data to study one of the following frontier topics in Galactic astrophysics:

  • Formation of the Galactic halo.
  • Formation of the Galactic bulge.
  • Formation of the Galactic thin and thick disks.
  • Globular cluster formation.
  • Chemical tagging.
  • Automatic analysis of stellar spectra.

There is a variety of projects that can be pursued within the broadly defined categories above, and the supervisor would be happy to discuss options with the students. In any event, there are already pre-defined possible immediate avenues for exploration, as listed below.

  • The history of star formation and chemical enrichment of the Galactic disk. The student will compare chemical evolution models and cosmological numerical simulations to APOGEE observations of the chemical compositions of several tens of thousands of stars spread all over the Galactic disk. Evidence for the occurrence of a recent burst of star formation across the disk will be examined, and its intensity and time of occurrence will be mapped across the disk.
  • Origins and evolution of the Galactic globular cluster (GGC) system - Globular clusters are the oldest known stellar systems in the Galaxy and their origins are still a matter of debate. APOGEE has amassed the largest ever spectroscopic data base of GGCs. This project has two main thrusts:
    • to better understand the mechanisms of formation of GGCs by correlating the chemical compositions of their with their global properties. This project will focus on better constraining the as yet unexplained multiple populations phenomenon in GGCs
    • to study stars currently being lost to GGCs (so called extra-tidal stars) to constrain their contribution to the stellar mass of the Galaxy and shed light into how GGCs dissolve into the field of the Milky Way.
  • Chemical and kinematic tagging of stellar populations of the Galactic halo - The Galactic halo was formed early in the history of the Milky Way galaxy via a combination of in situ star formation and accretion of satellite dwarf galaxies. The student will study the chemical compositions and kinematics of halo stellar populations in order to help establish the fraction of accreted and in situ stars, and the nature of the accreted systems.
  • Stellar Populations of dwarf satellites of the Milky Way - This project consists in the analysis of the chemical compositions of hundreds of stars belonging to satellites of the Milky Way, in order to assess their evolutionary state, comparing them with the properties of the stellar populations of the Milky Way halo, both accreted and those formed in situ.
  • Development of the WEAVE stellar abundance pipeline. The WEAVE survey will obtain high-resolution spectra for about 50,000 halo stars. Chemical compositions will be obtained from those spectra through an automatic abundance analysis pipeline, which is currently under development. The student will join efforts by our WEAVE collaborators at Nice Observatory to help in the development of the GAUGUIN pipeline. 

Modelling of gamma-ray burst, gravitational wave, and related astrophysical transients

Supervisor: Gavin P Lamb

Please note:
This project is only available for in-person students, not for distance learning students.

Gamma-ray bursts are the instantaneously most energetic explosions in the Universe and are linked to the formation of black holes via the merger of neutron stars and the collapse of massive star cores. These systems, especially neutron star mergers, produce detectable gravitational waves and the gamma-ray burst related transients are our best chance of detectable electromagnetic counterparts to gravitational wave signals. Gamma-ray bursts are followed by broadband afterglows and associated with certain types of supernovae and/or kilonova, where both of these thermal transients are the sites of nucleosynthesis for the heaviest elements on the periodic table. The modelling of the broadband afterglow and the spectra and light curves of associated transients can reveal the dynamics and composition of these highly energetic and relativistic explosions. This project will look at developing models for the various gamma-ray burst emission components and the application of these models to individual and populations of gamma-ray bursts and related transients. The aim of this project is to develop new models, and use state-of-the-art techniques to reveal the physics and diversity of dynamical properties within gamma-ray bursts and gravitational wave transients as well as search for signatures of heavy element nucleosynthesis.

Jets from Gamma-ray Bursts and Gravitational Wave Mergers

Supervisor: Shiho Kobayashi

Please note:
This project is only available for in-person students, not for distance learning students.

Gamma-ray bursts (GRBs) are instantaneously the most luminous objects in the universe, associated with relativistic jets. The core-collapses of massive stars or the mergers of binary compact stellar objects are their progenitors. The latter is the primary targets for gravitational wave (GW) observatories (e.g. LIGO, Virgo). In both cases, accretion onto a black hole is likely to power such jets. We will study the structures and other characteristics of relativistic jets using the electromagnetic (EM) counterparts of GW sources and “orphan" GRB afterglows together. This study also has the implications for the measurements of the Hubble constant using GW observations.

Using our numerical models, we will evaluate the light curves of off-axis jet for various jet structures to make predictions and to discuss the EM follow-up strategy for the current and upcoming surveys in optical and radio (e.g. ZTF, LSST, LOFAR, SKA). Although GW 170817 happened at a distance of 40Mpc, such local events seem to be rather rare. We will investigate whether we can statistically give constraints on jet structures by analysing many events together, or how many EM counterparts and orphan afterglows are needed to study jet structures. We will examine whether the structures of jets are universal (e.g. Gaussian), and whether jet structures are similar in the two classes of jets (core-collapse SNe vs compact-stellar mergers).

In the case of GW 170817, the late-time radio detection of superluminal motion played a crucial role to break the degeneracy between two competing models (i.e. jet vs semi-isotropic cocoon), we will numerically evaluate the radio and infrared images of various structured jets, and we will investigate how jet images are affected by the lateral and radial jet structure. We will also study what observable quantities (e.g. jet image size, centroid shift) are most sensitive to the viewing angle. We will develop the best scheme to evaluate the viewing angle from EM observations. GW sources accompanied by EM counterparts provides standard “siren” (the GW analogue of an astronomical standard candle) measurements of the Hubble constant. However, the degeneracy in the GW signal between the source distance and the viewing angle induces the uncertainty in its measurement. We will discuss how theY uncertainly can be reduced by using our numerical model when jet images are detected by VLBA, JWST and others.

Properties of Type Ia Supernovae and application to cosmology

Supervisor: Paolo Mazzali

Please note:
This project is available for both in-person (full-time) and distance learning students (part-time).

Type Ia Supernovae are luminous stellar explosions which can be observed out to redshifts corresponding to a time when the Universe was half its present age. They have been instrumental in the discovery of the acceleration of the Universe and Dark Energy. Yet, little is known about their physical properties, and even the nature of their progenitors is hotly debated, although we should expect that it should have a direct impact on the observed light display of the SN.

The underlying theme of this thesis is to further our understanding of SNe Ia, their physics, and their application in Cosmology. The thesis can be developed according to the student's vocation. The student working on this topic will have access to a large database of SN data (light curves and spectra), as well as to radiation transport codes which can be used to model the data and extract physical information.

The student can take part in observational campaigns (telescopes on La Palma and in Chile, observations with HST) and work on the analysis of the data; investigate the properties of existing datasets, looking for trends that may have a physical significance (e.g. properties that depend on SN luminosity or on host galaxy type); perform detailed modelling of individual SNe in order to determine their properties with a high level of accuracy and confidence; compare observational results with the predictions of theoretical models; work on extending and improving existing codes and testing these new tools.

There is now little doubt that there are different paths to make a SN Ia. This thesis should constitute a major step towards identifying which channels are possible, what are their observable manifestations, and which subgroups of SNe Ia can be ascribed to which particular channel. This would have a major impact on the confidence with which we use SNe Ia in Cosmology.

The student will have opportunities to work with a number of collaborators both in the UK and abroad while pursuing his/her thesis work.

The detailed properties of stripped-envelope Supernovae

Supervisor: Paolo Mazzali

Please note:
This project is available for both in-person (full-time) and distance learning students (part-time).

Massive stars end their lives when their core can no longer produce nuclear energy and collapses. This is followed by a powerful explosion, a core-collapse SN, where the stellar material that does not end up in a compact remnant (Neutron Star or Black Hole) is ejected. In about 1/3 of the cases, the progenitor star had lost either the outer Hydrogen envelope aor both the H envelope and the Helium shell. These SNe are collectively known as stripped-envelope SNe, and offer a clearer view into the inner parts of the explosion, revealing differences in the morphology and the energetics.

In this thesis, the student will use available data and collect new ones in order to increase the database of SE-SNe, and analyse in detail a few events in order to determine their physical properties with high accuracy. The student will work in together with a large team of observers and use available radiation transport codes to perform modelling. The exact balance of these activities will depend on the student's personal inclinations.

Superluminous Supernovae: a first attempt to develop a physical model

Supervisor: Paolo Mazzali

Please note:
This project is available for both in-person (full-time) and distance learning students (part-time).

Historically, two main types of SNe have been identified: Thermonuclear (Type Ia) and core collapse (all the rest). Recently, with the increased effort in observing SNe, new classes have been discovered that do not seem to conform with the paradigm above. One particularly interesting group is Superluminous SNe (SLSNe). As their name indicates, these are the most luminous transient events recorded. They can outshine SNe Ia by orders of magnitude, and can consequently be observed at cosmological distances.

This is however the only characteristic they have in common. SLSNe show a range of behaviours, suggesting that different physical events are called SLSNe. These may include Pair Instability SNe (the explosion of stars with mass exceeding 100 solar masses); interacting SNe, where the luminosity derives largely from the collision of SN ejecta with surrounding gas; magnetar-driven explosions of massive stars (40-80 solar masses).

This aim of this project is to understand what mechanisms can drive the observed phenomena. The student will start by becoming familiar with the available data and with SN theory in general. He/she will then try to apply or adapt existing models to the observations in order to test different scenarios. This may include using and modifying radiation transport tools or developing new ones specifically tailored for this class of events.

Developing an updated supernova radiation transfer code

Supervisor: Paolo Mazzali

Please note:
This project is available for both in-person (full-time) and distance learning students (part-time).

The Monte Carlo method is the tool of choice to perform radiation transport in the early phases of Supernovae and compute emerging synthetic spectra to be compared to observed ones. We pioneered this method and have used it successfully. With increased computing power, the time has come to create a new, expanded version of our code. The student will build and implement a larger database of atomic data, improve some of the simplest physical assumptions, perform test runs, and finally use the code to compare to observations. This project has a theoretical nature and is suitable for the theoretically minded student, with a good knowledge of maths and physics.