2008MNRAS.391..283V

Neutron star cores may be the hosts of a unique mixture of a neutron superfluid and a proton superconductor. Compelling theoretical arguments have been presented over the years that if the proton superconductor is of type II, then the superconductor fluxtubes and superfluid vortices should be strongly coupled and hence the vortices should be pinned to the proton-electron plasma in the core. We explore the effect of this pinning on the hydromagnetic waves in the core, and discuss two astrophysical applications of our results. (i) We show that, even in the case of strong pinning, the core Alfvén waves thought to be responsible for the low-frequency magnetar quasi-periodic oscillations (QPO) are not significantly mass loaded by the neutrons. The decoupling of ∼0.95 of the core mass from the Alfvén waves is, in fact, required in order to explain the QPO frequencies, for simple magnetic geometries and for magnetic fields not greater than 10¹⁵ G. (ii) We show that in the case of strong vortex pinning, hydromagnetic stresses exert stabilizing influence on the Glaberson instability, which has recently been proposed as a potential source of superfluid turbulence in neutron stars.