Star Formation and Protoplanetary Discs

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This research programme addresses key questions on how stars form from clouds of dust and gas in galaxies. We also investigate processes at work in the swirling discs that feed material onto the new stars: the very discs that evolve to form planets. Magnetic fields pervade interstellar space and play a crucial role in controlling how material can accumulate into ever denser cores as gravity takes hold during the collapse to a star-planet system. Even though stellar birth sites are cold and dense there are still some charged particles such as electrons, molecular ions and, importantly, charged grains of dust. We will investigate with computer simulations how the presence of charged dust grains affects the formation of stars and discs. Observationally we will study these processes using ESA's new Herschel satellite which will provide the first sensitive spectrum in the far-infrared region where many molecules emit. This will be coupled with detailed mapping of molecular emission from the ground with arrays of telescopes operating in the microwave region, and especially the new ALMA telescope in Chile with 66 dishes working in tandem. The chemical composition of these clouds and the insight from the blue- and red- shifts of their emission lines will allow us to infer what processes are controlling these crucial early stages in the birth of stars. The high level of spatial detail afforded by the new ALMA telescope will also be used to map out the infall onto stars much more massive than our Sun. Their formation 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. We will study a sample of massive forming stars which is close to being complete across the whole Galaxy, that we have found from following up an infrared survey of our Galaxy with the American MSX satellite. As the material gets close in to the star we expect it to complete its journey in a thin disc orbiting the star. We will systematically search our sample for these discs using the new technique of infrared interferometry which combines the light from two or three of the large 8 m telescopes of the VLT. In addition, we can use very high quality spectra from single telescopes to look for tiny spatial shifts from lines that arise from the disc relative to the starlight to gain 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. It is thought that magnetic fields are responsible for accelerating and channelling material into these jets. We will use the highly sensitive new network of radio dishes in the UK, e-Merlin, to map the emission from these jets and study how these plough into the surrounding infalling molecular material to blow holes in the cloud. The combination of radio, microwave and infrared observations across a wide range of masses and stages of evolution will enable us to disentangle the various competing processes at work. 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. The clumpy cloud gets shredded by the fast wind whistling through the less dense regions. As it slams into the molecular material it gets heated to millions of degrees and emits strongly in the X-ray region as observed with NASA's Chandra satellite. The winds colliding with each other can also accelerate particles and produce the so-called cosmic rays and we should see evidence of this at radio and gamma ray wavelengths. Computer simulations will be used to tackle this problem to investigate how these processes can terminate the star formation episodes in giant molecular clouds and in other galaxies where concentrated bursts of massive star formation take place.