Warwick Astronomy and Astrophysics Consolidated Grant 2017-2020

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What powers the most violent explosions in the Universe? What kind of galaxies host them? How do they relate to more normal galaxies? How do stars interact with each other in binary systems? When such stars spiral together, can we detect the tiny ripples in space-time that Einstein predicted and can we detect any light from such events? What are planets around other stars like? How many are there? What are they made of? These questions, which range from near neighbours in our Galaxy to the furthest reaches of the observable Universe, are those that the Warwick Astronomy and Astrophysics group will investigate. We will do so with a mixture of observations using ground- and space-based telescopes, theoretical developments and computationally-intensive numerical modelling. Although most of the Universe lies far beyond our direct reach, our understanding of physics allows us to extrapolate into regimes of unimaginable temperatures, densities, velocities and magnetic fields. Nevertheless, just as the most powerful computers can only forecast the weather for a few days in advance, the equations governing celestial objects can be formidably complex to solve, and we need observations to guide us. Starting in our backyard, a little over 20 years ago, the only planets we knew about were the planets of our own Solar System. Today, we know of more than 1000 planets around other stars, many of them extraordinarily different from our near neighbours. Warwick is the lead institute in a European collaboration to implement a new survey for Neptune-sized planets. The survey is based upon the decrease of light as the planets blocks light from the star. These are the most interesting planets to find because they allow us to measure both the mass and size of the planet. For a particular mass, the size of a planet depends upon its interior properties, opening up the remarkable possibility of probing the interiors of planets light-years from Earth. Incredibly, there is a more direct method still: we now know of dense, dead stars called white dwarfs which are surrounded by dusty disks of planetary building materials. As this material rains down onto the white dwarf, it is vaporised, allowing us to measure what it is made of. White dwarfs are usually highly stable, but very rarely, if enough matter is dumped onto them as can occur when they have a nearby companion in a binary system, they explode through uncontrolled nuclear fusion. This tears the entire star apart within a few seconds, in the process producing one of the optically-brightest explosions known along with most of the iron in the present day Universe. We are interested in understanding how these rare events come about. Such "supernovae" are so rare that we have to look beyond our own Galaxy to find them, and that is where even rarer and more exotic cataclysms are seen. The brightest explosions of all are the Gamma Ray Bursts (GRBs), which are rare, but so bright that they can be seen more than 10 billion light-years away in the distant Universe. Remarkably for such dramatic events, there seem to be multiple ways for them to occur. We aim to understand their underlying cause. Surprisingly, the most powerful events of all may be very dim to our eyes: when a pair of black-holes orbits one another, they spiral-in because of the emission of energy through "gravitational waves", ripples in fabric of space. Physicists are on the verge of sensing these with exotic arrangements of lasers and mirrors designed to pick up tiny perturbations of length. We want to *see* such events, a tough challenge because our gravitational wave "eyes" are poor at pinning down locations on the sky and the events may be very dim. Supernovae, GRBs and merging black-holes come from stars residing in galaxies. To understand them, we need to understand galaxies, how they form stars and how they evolve over the 13 billion year history of the Universe.