Equilibria and oscillations of magnetised neutron stars

We investigate equilibrium configurations and oscillation spectra of neutron stars,<br/>modelled as rotating magnetised fluid bodies in Newtonian gravity. We also explore<br/>the idea that these model neutron stars could have dynamics analogous to rigid-body<br/>free precession.<br/><br/>In axisymmetry, the equations of magnetohydrodynamics reduce to a purely<br/>toroidal-field case and a mixed-field case (with a purely poloidal-field limit). We<br/>solve these equations using a nonlinear code which finds stationary rotating magnetised<br/>stars by an iterative procedure. We find that despite the general nature of<br/>our approach, the mixed-field configurations we produce are all dominated by their<br/>poloidal component. We calculate distortions induced both by magnetic fields and<br/>by rotation; our results suggest that the relationship between the magnetic energy<br/>and the induced ellipticity should be close to linear for all known neutron stars.<br/><br/>We then investigate the oscillation spectra of neutron stars, using these stationary<br/>configurations as a background on which to study perturbations. This is done<br/>by evolving the perturbations numerically, making the Cowling approximation and<br/>specialising to purely toroidal fields for simplicity. The results of the evolutions<br/>show a number of magnetically-restored Alfv´en modes. We find that in a rotating<br/>star pure inertial and pure Alfv´en modes are replaced by hybrid magneto-inertial<br/>modes. We also show that magnetic fields appear to reduce the effect of the r-mode<br/>instability.<br/><br/>Finally, we look at precession-like dynamics in magnetised fluid stars, using both<br/>analytic and numerical methods. Whilst these studies are only preliminary, they<br/>indicate deficiencies in previous research on this topic. We suggest ways in which<br/>the problem of magnetised-fluid precession could be better understood.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2010

Author dc:creator

• Lander, Samuel Kenneth

Advisor dc:contributor.advisor

• Jones, D.I.