Solving cosmological questions in strong gravity

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My work seeks to answer two questions that go to the heart of cosmology - understanding what the Universe is made of, and where it came from.Firstly, what is dark matter? Dark matter is one of the main components of our Universe, but so far it has only been detected via its gravitational effect on stars and galaxies. I will identify how key properties of the particles that make up the dark matter, such as mass and spin, affect its clustering around black holes. I will then investigate how these dark matter environments affect gravitational wave and electromagnetic signals, linking these "multimessenger" observations to particle physics.Secondly, how did the Universe begin? I will explore the behaviour of our universe at the earliest times, when even small imperfections may blow up in a chaotic way. The aim is to understand how our universe emerged from a Big Bang to the state of uniform expansion that we observe - did non-uniform regions become synchronised? Can new types of matter act as a "cosmological smoother"? How did we escape the fate of a contracting universe?To answer these questions, I am using "numerical relativity" computational techniques. These tools were developed to allow the LIGO/Virgo network of gravitational wave detectors to interpret the signals they see from merging black holes and neutron stars, but are now attracting attention in other areas of theoretical physics. I am pioneering their application to cosmological questions, a nascent field which harnesses the power of modern supercomputing to answer long-standing questions about our Universe.