Cullan Howlett

Mapping the Universe with DESI and 4HS

Maps of the positions of millions of galaxies in our Universe are used to refine our understanding of its components and evolution. However, these experiments have left us with more questions than answers. What is the nature of dark energy and dark matter? Is Einstein’s theory of General Relativity correct on scales beyond our solar system?

Upcoming surveys aim to answer these questions. But understanding how the distributions and motions of galaxies relate to fundamental physics and how to sift through this enormous amount of data to uncover the truth requires improving our analysis techniques and developing new ways to use the data.

Many projects are available under this theme, with different emphasis on mathematical theory, data analysis or computer programming. They could involve improving and speeding up methods for simulating the Universe on supercomputers. Or developing new mathematical models for describing how galaxies cluster and move relative to each other. Or, they could involve using real measurements of positions and velocities of galaxies we are currently obtaining or working towards with surveys such as the Dark Energy Spectroscopic Instrument, WALLABY, or the 4MOST Hemisphere Survey.

Cosmology with gravitational waves

Gravitational waves are ripples in space-time that propogate away from massive compact objects as they merge, to hopefully, eventually, be detected here on Earth by the LIGO/Virgo gravitational wave detectors. Gravitational waves hold information on some of the most exotic objects in the Universe such as black holes and neutron stars. They can also be used to test cosmological models, particularly because they act as "Standard Sirens" - the gravitational waveform tells us how far away the merging objects are which then can be used to work out how fast the Universe is expanding and how fast it's large scale structures are growing.

This project will look at techniques for extracting Standard Siren measurements from gravitational waves. In particular, developing simulated catalogues of gravitational wave events and then using these simulations to work out how best to extract cosmology from the real data. This project brings together a range of fields, from understanding the details of how black holes and neutron stars are formed, to theoretical modelling of future cosmology studies that might be possible once we have hundreds of gravitational waves.