Giant Hall Waves Launched by Superconducting Phase Transition in Pulsars

Abstract

The cores of pulsars are expected to become superconducting soon after birth. The transition to type-II superconductivity is associated with the bunching of magnetic field lines into discrete superconducting flux tubes which possess enormous tension. The coupling of the crust to the flux tubes implies the existence of huge tangential magnetic fields at the crust-core interface. We show that the transition to superconductivity triggers a highly non-linear response in the Hall drift of the crustal magnetic field, an effect which was neglected in previous numerical modelling. We argue that at the time of the phase transition giant Hall waves are launched from the crust-core interface toward the surface. Our models show that if the crust contains a multipolar magnetic field $\sim 10^{13}$ G, the amplitude of the Hall waves is $\sim 10^{15}$ G. The elastic deformation of the lattice is included in our models, which allows us to track the time-dependent shear stresses everywhere in the crust. The simulations indicate that the Hall waves may be strong enough to break the crust, and could cause star quakes which trigger rotation glitches and changes in the radio pulse profile. The Hall waves also couple to slow magnetospheric changes which cause anomalous braking indices. The emission of the giant Hall waves from the crust-core interface facilitates fast flux expulsion from the superconducting core, provided that the flux tubes in the core are themselves sufficiently mobile. For all of the flux tube mobility prescriptions implemented in this work, the core approaches the Meissner state with B=0 at late times.