Magnetohydrodynamic Stability of Magnetar Cores and Crusts

Magnetars are neutron stars possessing the strongest known magnetic fields, with surface fields of 1e14-1e15 G and interior fields likely one or two orders of magnitude stronger. At these field strengths, Landau quantization of fermions modifies the thermodynamic and transport properties of neutron star matter. I will discuss how Landau quantization can also affect the magnetohydrodynamic (MHD) stability of a neutron star threaded by magnetar-strength magnetic fields. First, I will describe its effects on the stability of the core fluid, where an ideal MHD canonical energy principle is used to determine the stability of a toroidal field. The existence of an instability analogous to that of flux tubes in magnetized superconducting fluids will be detailed, and connected to the formation of magnetic domains within the core. I will then discuss how the strong-field Landau quantization effects modify the MHD oscillation modes of a neutron star crust, in particular discussing how the Hall (whistler) modes in this region can become unstable. This instability is demonstrated using linear mode analysis and preliminary numerical simulations.