New frontiers in transient astrophysics: gravitational-wave multi-messenger events and exotic stellar explosions

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How and where did the elements of the Universe form? How do stars live and die? What happens when two of the densest objects in the Universe crash into each other? Where do the brightest flashes of light in the Universe come from? What is the ultimate fate of the Universe? These are some of the questions that lie at the heart of the research to be undertaken by this fellowship. The fellowship will exploit the UK's premier sky survey to detect new transient objects in the Universe, and undertake innovative approaches to studying these objects in order to further our understanding of the Universe.When massive stars, more than 8 times the mass of our Sun, reach the end of their lives, they collapse due to their own gravity and produce a neutron star or black-hole. During this rapid and catastrophic collapse, large amounts of chemically-enriched material is expelled into the Universe in an extremely luminous event known as a supernova. These chemically-enriched innards are essential for life as we know it, containing carbon, oxygen and iron. Through supernova explosions, these elements form the next generation of stars and planets, seeding the building blocks of life. Our understanding of supernovae is hampered due to time lags between telescopes discovering the supernova, and larger telescopes then taking detailed observations. This fellowship will create a world-leading rapid observatory network to overcome this. Using the UK-led GOTO telescope system to discover new supernovae and automatically triggering larger telescopes nearby, we will routinely perform detailed observations within hours of discovery, and minutes in some cases. Opening this new timescale of investigation provides vital diagnostics on the nature of the exploding stars (such as their size and mass) and the energetics and chemical makeup of the explosion itself. These are essential for us to build a complete picture of how different stars die, and how the chemical fingerprint of our Universe was formed.After massive stars die, their journey is not quite complete - recent breakthroughs mean we can now detect them 'beyond the grave' as their neutron star and black hole corpses violently merge. A truly landmark moment in history occurred in 2015 when the LIGO/Virgo detectors found a completely new signal from the Universe: minute ripples in space-time. These ripples were caused by two black holes merging 1.3 billion light years away and are known as gravitational-waves - their detection was the fruition of a century-old prediction by Einstein. As well as seeing, with the detection of gravitational-waves, we are now 'hearing' the Universe.Just as our senses combine to give us far more information than they do alone, so too does combining light we see and gravitational-waves we hear from astrophysical transients. This 'multi-messenger' era of gravitational-wave research began in 2017 with the first ever event discovered in both light (photons) and gravitational-waves. The event, named GW170817, was the result of two neutron stars colliding around 130 million light years away and became one of the most intensely studied objects in the Universe. The findings from this single event are mesmerising, but it also raised many further questions. We only have one example of this kind of event. To make progress we must observe a population of similar events to understand their diversity and how often they occur in the Universe. Finding these objects is not trivial however, and, akin to the 'needle in the haystack' problem, it requires rapidly looking at huge swathes of the night sky to find the single correct counterpart to the gravitational-wave signal. By developing the GOTO system, designed explicitly to perform this task, and leading analysis of new gravitational-wave multi-messenger events with premier international facilities, this project will be at the forefront of the international effort to realise the potential of this exciting new window on the Universe.