Astronomers at Warwick will use a technique called interferometry to see faint planetary debris swarming close to bright stars, where glare normally hides it. This matters because we still do not know what most exoplanets and their building blocks are actually made of—our Solar System’s composition is just one data point. The team will also study white dwarfs, the ultra-dense remnants of dead stars, whose atmospheres sometimes show heavy elements from infalling planetary material. Because white dwarfs have gravity 200,000 times Earth’s, only hydrogen or helium should be visible; seeing heavier elements means we are witnessing planetary systems being consumed in real time. This gives a direct chemical fingerprint of exoplanets and asteroids. The research is fundamental science with no immediate practical application. But similar curiosity-driven work—like the interferometry now used here—was once itself a niche technique, and white dwarf cooling has already become a way to date the Galaxy’s star formation history. A deeper understanding of how planetary systems form, evolve, and die could eventually inform models of how common Earth-like compositions are in the Universe.
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How do stars, galaxies and planets form? What are they made of? How do they die? These are some of the questions addressed by the research programme of the Warwick Astronomy and Astrophysics group. Answering them is becoming possible in ways not imagined just 5 years ago. We now know of thousands of planets outside our Solar system, many of them exotic worlds closer to their stars than even Mercury is to the Sun. These planets are seen against overwhelming glare from their host stars, but remarkably it is now possible to tease out information on their compositions imprinted in their star's light as it passes through their atmospheres. The Solar system contains not just planets, but debris in the form of comets, asteroids and dust left-over from their formation. Other solar systems do too, but again the glare from stellar hosts makes it hard to see this material. A cutting-edge technique called interferometry allows us to see faint sources close to the star; we will use this to study remnant planetary material. The same planetary material can survive the entire lifetime of the stars until all that remains of the stars are hot, ultra-dense remnants known as white dwarfs. White dwarfs have extraordinary gravities, 200,000 times that of Earth, so high that only the lightest elements, hydrogen or helium, are typically visible in their atmospheres. How then do some of them show heavier elements? We believe that we are actually seeing recent or even present-day accretion of their remnant planetary disks. It is remarkable that this happens at all because just before turning into white dwarfs, stars swell by one hundred times in size, and should clear all planetary material out to a distance corresponding to Earth's orbit and beyond. Nevertheless, this gives us a unique insight into the composition of extra-solar planets and planetesimals, and is work that will be pursued in this grant. White dwarfs themselves are sites of exotic physics, allowing us to test quantum mechanics in dense fluids and to see matter in magnetic fields far stronger than can be generated on Earth. They are archaeological remnants of the history of our Galaxy, which betray their ages not through radio-carbon dating, but temperature, as they cool so slowly that they can still be detected over 10 billion years after formation. As a result of the Gaia satellite, we now know of more than 250,000 white dwarfs; we will carry out theoretical research to map the history of our Galaxy through its star formation. We will search these stars for pulsars, stellar lighthouses driven by rotating magnetic fields. Star formation and how it evolves crucial to our understanding of other galaxies, and how they build up chemical elements, right back to the most distant galaxies visible in the far Universe. We have developed models which account for the unusual evolutionary pathways made possible in binary star systems (close pairs of stars). We aim to build a consistent model of the build up of chemical elements which will be needed to interpret the observations soon to flow from the next great mission of astronomy, the James Webb Space Telescope (JWST). Looking far outside our Galaxy, we can encompass millions of other galaxies, allowing us to see events that may only occur once in 100,000 years in our own Galaxy. This has recently allowed the detection of ripples in space-time from the violent merger of black-holes and the super-dense neutron stars, processes that may form much of the heavy element content of the Universe. We will pursue the detection of such events in visible light through rapid-alert observation of wide areas of the sky. Finally, returning closer to home, the same wide-field observations have found many of the most interesting known exo-planets by seeing them pass in front of their host stars. We will follow such systems found near bright stars by NASA's TESS satellite in order to probe planet formation and planetary atmospheres.
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