Are there any stable magnetic fields in barotropic stars?

April 2012

Sam Lander, Ian D. Jones

We only observe the exterior magnetic fields of stars; for neutron stars we can typically just infer the dipole component, from the rate at which the star's spin rate decreases. By contrast, knowing the interior field would help us understand many phenomena of neutron stars: their long-term evolution, oscillation modes and occasional dramatic flaring events. Without having direct observations, we can try to model the magnetic field inside a neutron star - a good model should be a stable equilibrium solution.

Much previous literature has assumed that a barotropic star - where the pressure is a function of density - is a good first approximation. In this case, the expectation was that a magnetic field geometry combining poloidal and toroidal components would be stable. We used numerical simulations to show that this assumption was generically wrong - the magnetic fields were unstable! Our work suggests that more advanced modelling may be crucial to finding a good model of a magnetised neutron star.

MNRAS, 424, 482 (2012) arXiv:1202.2339v1 [astro-ph.SR]