Lumpy, bumpy star-forming clouds (astronomy and astrophysics): Investigating the idea that star formation is an example of Self-Organised Criticality

The clouds where stars form are highly turbulent. This means that the densities and velocities of the gas in the cloud have a big range of values. There are dense lumps of gas, and there are rarefied regions in between. The dense lumps often have supersonic bulk velocities, so they bump into one another, and this is probably what triggers star formation. The aims of this project are to simulate the formation of shock-compressed sheets, filaments and prestellar cores in a turbulent interstellar cloud; to explore carefully the parameters characterising interstellar turbulence and to establish how they influence the properties of the sheets, filaments and prestellar cores that form, and what distinguishes those that go on to form stars from those that don’t; to determine the external appearance of sheets, filaments and cores as they form, fragment and collapse to form new stars and to identify robust observational
signatures for the different stages; and to determine the circumstances under which turbulent fragmentation forms stars with a mass distribution and binary statistics matching observed stellar populations. In particular, we will investigate the idea that star formation is an example of Self-Organised Criticality. in which the critical process is thermal coupling between gas and dust, which only occurs at relatively high densities. The investigation will use Smoothed Particle Hydrodynamics, and will start with simple self-gravitating hydrodynamics and a barotropic equation of state; then thermal, radiative and chemical processes will be added; and finally we will incorporate the scheme of Hosking & Whitworth (2004) for treating non-ideal magneto-hydrodynamics, and explore what in
uence this has. The student will become expert in interstellar gas dynamics and the associated chemical and radiative processes,
star formation, and numerical magneto-hydrodynamics.