PhD Projects

Testing the nature of dark matter on small scales

Prof. Ian McCarthy, Dr Andreea Font

A number of tensions between the predictions of the standard model of cosmology and observations of the matter distribution on "small" scales (e.g., within the Local Group) have arisen in recent years, leading some cosmologists to speculate that our current ideas about dark matter are not correct.  Specifically, the dark matter may not be a heavy/cold particle but may consist, at least in part, of a lighter/warmer species and/or that the dark matter is able to interact with itself in interesting ways.  While implementing such possible behaviours in cosmological simulations is now becoming more common, very little is currently known about how such processes may interact with processes that are important for galaxy formation, such as radiative cooling, star formation, and feedback processes.
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Dark energy, massive neutrinos, and cosmic feedback

Prof. Ian McCarthy

Upcoming surveys of large-scale structure (LSS), including Euclid, LSST, and DESI, aim to measure the distribution of matter in the Universe on large scales to percent level accuracy with the goal of rigorously testing the standard model of cosmology.  In addition to strongly constraining the standard model, the holy grail would be to detect deviations from it, including an unambiguous detection of massive neutrinos and possibly a deviation from a cosmological constant.  However, precise theoretical predictions are required to achieve these goals and this necessitates the use of large cosmological hydrodynamical simulations which correctly capture the impact of cosmic feedback which can alter the matter distribution much more strongly than the cosmological effects we are looking for.
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Reconstructing the formation history of the Milky Way and other nearby galaxies

Dr Andreea Font, Dr Marie Martig

Recently, major progress has been made in deciphering the assembly history of our own Galaxy, the Milky Way. Some of the key discoveries were enabled by the advent of Gaia, a high precision astrometry space mission that has mapped our Galaxy in much greater detail than was ever possible before. From the debris found in the Milky Way’s stellar halo, it was found out that a fairly massive galaxy (dubbed Gaia Enceladus) has merged with the Milky Way more than 9 billion years ago. This important event may have affected the structure of the galactic disc, by thickening it, by ejecting stars out to large distances in the halo, or by flipping its axis of rotation.
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Gamma-Ray Bursts with MOPTOP

Prof Iain Steele, Dr Helen Jermak, Prof Shiho Kobayashi

Gamma-ray bursts are some of the most energetic transient events in the universe, they are powered by relativistic jets produced by neutron star mergers and the collapse of massive stars. Although the acceleration and collimation processes of GRB jets (and other relativistic jets from compact objects)  are still open questions, recent observations imply the importance of magnetic acceleration processes (e.g. the magnetic field around the compact object becomes twisted and amplified by the rotation and the magnetic pressure accelerates the jet). According to the magnetic models, the magnetic field in the jet is expected to be well ordered, while alternative models predict random magnetic fields or a patchwork of unaligned magnetic regions. Since photons are produced by the synchrotron process, they are polarised perpendicular to the magnetic field lines in each fluid element of the emission region. The net polarisation signals depend on the geometry and relativistic effects.
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The search for intermediate-mass black holes

Dr Sebastian Kamann, Dr Renuka Pechetti

A long-standing question in astrophysics is whether intermediate-mass black holes exist. With masses between 100 - 100,000 Msun, such black holes would fill the observed gap between the stellar-mass black holes and the supermassive black holes. The centres of massive star clusters have been suggested as promising hideouts for intermediate-mass black holes, as the high stellar densities near the cluster centres are a conducive environment for black holes to grow. Additionally, some clusters have been suggested to be the remnants of dwarf galaxies and hold a high chance of still hosting the massive black holes formed in said galaxies.
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GLIP: A new concept in full Stokes Astronomical Polarimetry

Dr Éamonn Harvey & Prof Iain Steele

Optical polarimetry is a probe of physical and magnetic field geometries in many otherwise spatially unresolved astronomical sources. Polarization is now taking a leading role as a key diagnostic of physical conditions (magnetic field strength/order/geometry and relativistic plasma dynamics) in time variable sources such as blazars, active galactic nuclei, x-ray binaries and gamma ray bursts. In these high energy sources, polarization allows astronomers to probe the physical conditions at spatial scales that will never be accessible to direct imaging observations. However, the majority of large telescopes do not host polarimeters. There are several reasons for this. Traditionally polarimetry is seen as a “hard” technique, requiring specialist knowledge by the observer in data reduction. It is also seen as one that is expensive to implement, maintain and calibrate due to its complexity.
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A new stellar population synthesis model library

Prof. Maurizio Salaris

One of the major open questions in modern astrophysics is the origin and evolution of galaxies. One way to address this problem is to study the star formation histories (SFHs) of galaxies of different types, which tells us the rate at which gas is transformed into stars and the evolution of its chemical composition. The large majority of galaxies are so distant that we can observe only their integrated light, the sum of the light of all their stars, and the challenge is to decode the information on the SFH imprinted in this light. Stellar population synthesis techniques do exactly this. Using stellar evolution model libraries and stellar spectra, we can calculate integrated magnitudes and spectra of distant galaxies, and develop methods to derive their SFHs.
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Near field cosmology: the genesis of the Milky Way Galaxy

Dr Ricardo Schiavon

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 curring-edge surveys of Milky Way stars, including APOGEE, WEAVE, and MOONS, in order to determine the chemical compositions of an unprecedented sample of over one million stars, and establish the history of star formation and mass assembly of the Galaxy.  Specifically, the student will explore the data to study one of the following frontier topics in Galactic astrophysics:
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The Complete Landscape of Massive Stellar Death

Dr Dan Perley

The time-domain sky is unexpectedly diverse: over the past decade we have come to realize that stars can explode in a wide and diverse manner of ways that had not previously been predicted.  But we do not yet know what sets the pathway a massive star will follow to its death. Fortunately, a generation of new telescopes is now scanning the skies every night and accumulating supernova discoveries in the hundreds, permitting exquisite samples to be collected.  In this project a student would help to discover new supernovae, and compile catalogs of existing supernovae and their host galaxies to address the question of exactly what it is that governs the manner in which the biggest stars die.
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Galaxy demographics

Prof. Ivan Baldry and others from extra-galactic or cosmological-simulation groups

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.
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Relativistic outflow from gravitational wave mergers

Prof Shiho Kobayashi

Gravitational waves (GWs) are one of the most remarkable predictions of Einstein’s general theory of relativity. These ripples in the curvature of space-time are caused by some of the most violent and energetic processes in the Universe, such as coalescing compact stellar objects (black holes, neutron stars) and supernovae.  With further improvements planned for the current GW detectors (LIGO, Virgo, and KAGRA) and other GW detectors (LIGO India) coming online, a large number of GW events are expected to be discovered in the coming years (the new observing run O4 is expected to start  late 2022).  Of particular interest are neutron star - neutron star (NS-NS) and black hole - neutron star (BH-NS) mergers. These mergers are leading candidates for short Gamma-Ray Burst (GRB) progenitors and the primary targets for the ground-based GW observatories.
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What controls where life can form and evolve in the Universe?

Prof Steve Longmore

This PhD project tackles the question, “What controls where life can form and evolve in the Universe?”. In recent years, extrasolar planet surveys have found planetary systems are ubiquitous around nearby stars and these planets have a bewildering array of properties. But what mechanisms determine the properties of planets and whether they can sustain life? This PhD project will use high sensitivity and resolution ALMA observations of proto-stellar and proto-planetary systems in extreme environments to quantify how the birth environment affects a star’s long-term potential to host habitable planets. This is a key step towards understanding where we expect to find life in the Universe.
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