A Programme of Astrophysical Research at Leeds

This research programme principally addresses how stars and planets form and evolve.

Stars form from the clouds of gas that occupy interstellar space and the small dust grains mixed in them. The formation of stars much more massive than our Sun has proved to be much more difficult to understand as they are rare and distant and produce prodigious amounts of radiation that blow material away rather than let it fall in. As the infalling material gets close in to the star we expect it to complete its journey in a thin disc orbiting the star. Detailed mapping of the molecular emission with the ALMA telescope will reveal whether these discs are stable or whether they will fragment to form binary systems. The inner regions of these discs are hotter and will be studied using the techniques of infrared interferometry and spectroscopy. This reveals spatial information at levels 10 to 100 times better than the Hubble Space Telescope. At the same time that material is spiralling onto a star via a disc, some of it is being ejected at high speeds along the rotation axis, most likely driven by magnetic fields. To follow these jets further out we will use radio telescopes including the network of radio dishes in the UK, e-MERLIN, to map their emission. We will look for links between bursts of material falling on to the new star with ejections of material along the jets. Most stars form in clusters, but the way in which such systems form and evolve is hotly debated. New information from ESA's Gaia satellite that measures accurate distances and motions of stars will be used alongside other data on the molecular gas clouds to compare with simulations. Novel statistical techniques will be developed to undertake this multi-dimensional comparison.

The discs that surround stars like the Sun as they are forming are the sites where planets form, built up from the coalescence of dust grains. A survey of the properties of these discs around stars slightly more massive than our Sun will be carried out to study the phase when the leftover gas is being blown away and collisions between proto-planets is creating belts of dust. A high resolution study of the chemical make up of planet forming discs will be carried out with the ALMA telescope to look for complex organic molecules in the planet-forming and comet-forming outer reaches. These molecules could be important in the origins of life. A laboratory study will measure key chemical reaction rates needed to find out how some of the most interesting molecules on the pathway to biological systems are formed. These will be incorporated in to chemical models of the discs to address questions on the origins of life. The habitability of Earth-like planets around other stars will be investigated by looking at the effect of their host stars variable output of radiation on the loss of the atmosphere of the planet.

Near the end of the lives of stars, the very dust grains that begin the planet formation process are themselves produced. We will perform detailed chemical calculations to work out how these silicate minerals are built up from the gaseous elements in the rich, cool, atmospheres of giant stars. Massive stars blow very strong winds from their surfaces as they evolve and when they are in binaries these winds smash together. This accelarates charged particles up to close to the speed of light which generates distinctive emission in the radio, X-ray and gamma ray wavebands, which we will simulate to understand these processes. A similar situation pertains when the jets from young stars hit the surrounding gas. The fast particles produced are called cosmic rays and pervade the Galaxy. A new survey of our Milky Way with the MeerKAT radio elescope in South Africa has revealed a network of filaments of emission. We will investigate this new phenomena in the interstellar gas and its relationship to sources of cosmic rays.