Warwick Astronomy and Astrophysics Rolling Grant 2011-2016

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The Universe is constantly changing. On timescales of millions of years, stars are born, live and die, and in hundreds of millions of years, entire galaxies come into being. At some stages, the lives of stars can be dramatically sped up and we can see changes happening in days, hours or even seconds. The incredible advances in computer technology of the last decades is now allowing astronomers to track such events in large numbers. At one extreme are the distant 'Type Ia' supernovae used to probe perhaps the deepest mystery of modern physics, the dark energy now thought to be driving an increasing rate of Universal expansion, while at the other are surveys that have found hundreds of other worlds around stars a few light-years from Earth. Some of the most rapidly variable objects of all are the dense remnants left at the end of stars' lives (white dwarfs, neutron stars and black-holes). Pairs of such stars orbiting at up to 1000 orbits per second radiate perturbations of the geometry of space called gravitational waves. Experiments are well underway to detect such ripples and provide the first direct tests of Einstein's great tour-de-force, the theory of General Relativity. Type Ia supernovae are bright but rare so although we can see them in the distant Universe, they only very rarely occur near enough to study in detail; we have not seen one in our own Galaxy for over 400 years. Thus, although we know that they are caused by exploding white dwarfs, we don't know precisely what sort of systems produce them. Yet, there must be many potential supernovae in the nearby Universe. We will pursue a program to understand such potential progenitors with the aim of understanding their numbers and evolution. We will employ a combination of discovery from surveys covering large areas of sky followed by detailed study of individual objects in order to understand both their past and future evolution. These are the data needed to test and develop the models of binary star evolution from which we can predict the extent of the evolution of Type Ia supernovae during the history of the Universe, crucial for their use as probes of dark energy. The same models are required to predict the number and properties of gravitational wave sources, essential for the development of the gravitational wave detectors themselves. The most extreme variable sources of all are gamma-ray bursts, staggeringly bright explosions which take us back to the young Universe. Gamma-ray bursts are stellar explosions which allow us to pinpoint galaxies early in their lives. Recent work on gamma-ray bursts by the group has been led to the discovery of the most distant objects ever seen. We will pursue these with an array of observations from large ground- and space-based telescopes such as the Hubble Space Telescope and the European Southern Observatory's Very Large Telescope to probe the conditions that lead to the formation of the first stars in the young Universe. Our work in following up gamma-ray bursts may help the search for gravitational waves by narrowing the range of models needed to perform such searches. We now know many more planets (over 400) around other stars than exist within our own solar system. These other worlds have revealed an unexpectedly dynamic past involving planet-planet interactions flinging some planets towards their stars and others out of their reach altogether. All surveys for such systems tend to favour large, massive planets. We will develop a new camera sensitive to smaller planets, comparable to Neptune in the solar system. We will use the same techniques needed to understand binary systems to probe extra-solar planets by looking through their atmospheres to their host stars. We will use the Hubble Space Telescope to measure element abundances of extrasolar planetary material around white dwarfs and use the clock-like precision of white dwarfs in binary systems to detect planetary companions.