In this thesis we investigate the development and use of numerical methods to study astrophysical problems, particularly the formation and evolution of objects via gravitational instability in circumstellar discs. We begin with a comprehensive overview of the development, validation and optimisation of numerical tools. These formed the basis of SEREN, a Smoothed Particle Hydrodynamics (SPH) code for modelling self-gravitating fluid dynamics. SEREN has been rigorously tested and optimised, and is now being used for high-performance research in various areas of star formation. We then consider in some depth the problems associated with shocks, instabilities and shear flows in numerical simulations, detailing why such problems arise and what can be done to alleviate them. Finally we model circumstellar discs, investigating the influence of both physical and computational parameters upon the formation of objects via gravitational instability. We then model the interaction of discs with stars and other disc systems, investigating the influence of the orbital parameters upon the evolution of a marginally stable disc. Ultimately we find that gravitational instability in massive extended circumstellar discs is a viable mechanism for the formation of brown dwarfs and massive planets, and provides an explanation for the "brown dwarf desert" and free-floating planets. We also find that while disc-star and disc-disc interactions might produce accretion bursts and exert an influence over the disc evolution, they are not a likely mechanism for triggering fragmentation in marginally stable discs.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:567110 |
| Date | January 2011 |
| Creators | Batty, Christopher Peter |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://orca.cf.ac.uk/8570/ |
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