Special Astrophysics Seminar

Electric currents in the crust and the magnetosphere of neutron stars

Kostas Gourgouliatos

Durham University

From explosive events in magnetars to the spin-down of rotation-powered pulsars, the magnetic field and the associated currents play a central role in the lives of neutron stars. First, I will discuss the consequences of the Hall effect to the crustal magnetic field evolution and the crucial differences between axially symmetric and 3-D configurations. 3-D systems allow the spontaneous formation of kilometre-wide magnetic spots due the Hall instability, which is suppressed in axisymmetric configurations. Such spots could be possibly related to the emitting regions of magnetars. Then, I will discuss the limitations of the Hall effect once the induced stresses lead to crust yielding. The stresses may then be released through a plastic flow opposing the current responsible for the Hall effect. Finally, considering rotation-powered pulsars I will focus on the magnetospheric current closure question. Using a minimisation argument, one can solve for the flow of the magnetospheric current through the crust, which is responsible for the torque spinning-down the pulsar. It is found that the magnetospheric current reaches the deeper parts of the crust in millisecond pulsars, while it penetrate the crust for only for a few tens of meters in slowly rotating ones. The implications of this effect to the rotational evolution of pulsars will be discussed.