Astrophysics at the University of Birmingham - Consolidated grant 2022-2025

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The Universe looks very different depending on how we observe it. The use of a broad range of cosmic messengers, the full spectrum of "electromagnetic radiation" - ranging from radio waves through infrared radiation and light, to X-rays and gamma rays - and, as of only a few years ago also ripples in space and time known as gravitational waves reveal that the Universe is not a quiet place. It is characterised by violent and dramatic phenomena, powerful explosions that produce astonishingly large mount of energy over short periods of time. We can now study many of these catastrophic events in great detail thanks to a large range of superb observatories, some of which coming on-line in the next couple of years. We may be very surprised yet again, and discover new phenomena.Our programme looks at some of the most exciting transient phenomena from many different angles and has black holes and extreme ("compact") objects at its centre. We aim to study how black holes devour and shred stars at the centre of galaxies. We will use the effect of bending of light over cosmic scales to observe through massive lenses - groups and clusters of galaxies - multiple images of some of these catastrophic events, gain new insights about their engines and how the Universe evolves as a whole. We will also try to "hear" for the very first time the cosmic whisper of the population of billion solar mass black holes paring up at the centre of galaxies and radiating gravitational waves. We believe we can detect this radiation now with powerful galactic scale "instruments", the ultra-stable clocks provided to us by radio lighthouses known as pulsars. If this happens, we would open a new observational window on the Universe.Black holes are also spectacularly simple objects. They are a sort of fundamental particle of gravity and testing their properties is of paramount importance. Using the many binary black holes that we now routinely observe with gravitational-wave laser interferometers we will test to unprecedented accuracy one of the most famous predictions surrounding these objects: Hawking's horizon area theorem.Most or all of the cosmic explosions that we have described above take place in galaxies, which astronomers have studied in great detail for many decades. However, how galaxies form and evolve as part of the tangled structures in the Universe known as "the cosmic web" is still surrounded by mystery. New powerful surveys using some of the best telescopes in the world will allow us to put existing theoretical models under test, and we will gain new insights about galaxy evolution over cosmic time and the myriad of interlinked physical processes that take place in these environments.