A Programme in Astrophysical Theory and Observations at Leeds

This research programme principally addresses how stars and planets form from clouds of dust and gas. Stars form from the clouds of gas that occupy interstellar space and the small dust grains mixed in them. The clouds are highly filamentary and magnetic fields, that also pervade space, are likely to have had a role in shaping them, and controlling their collapse under gravity to form stars. We will conduct computer simulations to ascertain how the beginning of the formation of stars like our Sun takes place. The formation of stars much more massive than our Sun has proved to be much more problematic 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 is beginning to reveal these discs. We will significantly extend these initial discoveries and interpret the data with sophisticated models to find out how material flows into these discs. The rich spectra due to molecules at these wavelengths will be explored with novel data mining techniques to search for ways that we can trace changes over time as these stars form. The inner regions of these discs where the material completes its journey on to the forming star will be studied using the techniques of infrared interferometry. This reveals spatial information at levels 10 to 100 times better than the Hubble Space Telescope, where we may start to see the material being channelled by magnetic fields instead. 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, again most likely by magnetic fields. To follow these jets further out we will use the highly sensitive network of radio dishes in the UK, e-MERLIN, to map their emission. Comparison with complex models will show whether particles are being accelerated to relativistic speeds in these jets, further enhancing their potential impact on their environment. As massive stars finally begin to clear away the material from which they were born the combined effect of the winds driven by their strong radiation fields has a dramatic effect. As the winds slam into the molecular material and each other they get heated to millions of degrees and emit strongly in the X-ray region as observed with NASA's Chandra satellite. The most massive stars have such short lives of a few million years that they can blow up as supernovae whilst still surrounded by the remnants of the molecular clouds. Computer simulations will be used to tackle this problem to investigate how these processes can terminate the star formation episodes in giant molecular clouds. 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. This is only thought to occur in the quieter regions of the disc where turbulence due to the magnetic fields is less strong. We will perform calculations of the chemical effects that occur where the icy grains are sublimated that then affect their charge, and hence, magnetic properties. How the charged dust particles move relative to the gas is important in the formation process and that will be examined with sophisticated computer simulations. 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. Many of these heavier elements themselves are first made in the exploding stars known as supernovae. We will perform state-of-the-art simulations of the thermo-nuclear detonation of these stars, and examine how this affects the production of elements in the cosmos.