We investigate equilibrium configurations and oscillation spectra of neutron stars, modelled as rotating magnetised fluid bodies in Newtonian gravity. We also explore the idea that these model neutron stars could have dynamics analogous to rigid-body free precession. In axisymmetry, the equations of magnetohydrodynamics reduce to a purely toroidal-field case and a mixed-field case (with a purely poloidal-field limit). We solve these equations using a nonlinear code which finds stationary rotating magnetised stars by an iterative procedure. We find that despite the general nature of our approach, the mixed-field configurations we produce are all dominated by their poloidal component. We calculate distortions induced both by magnetic fields and by rotation; our results suggest that the relationship between the magnetic energy and the induced ellipticity should be close to linear for all known neutron stars. We then investigate the oscillation spectra of neutron stars, using these stationary configurations as a background on which to study perturbations. This is done by evolving the perturbations numerically, making the Cowling approximation and specialising to purely toroidal fields for simplicity. The results of the evolutions show a number of magnetically-restored Alfv´en modes. We find that in a rotating star pure inertial and pure Alfv´en modes are replaced by hybrid magneto-inertial modes. We also show that magnetic fields appear to reduce the effect of the r-mode instability. Finally, we look at precession-like dynamics in magnetised fluid stars, using both analytic and numerical methods. Whilst these studies are only preliminary, they indicate deficiencies in previous research on this topic. We suggest ways in which the problem of magnetised-fluid precession could be better understood.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:518553 |
| Date | January 2010 |
| Creators | Lander, Samuel Kenneth |
| Contributors | Jones, David |
| Publisher | University of Southampton |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://eprints.soton.ac.uk/167473/ |
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