Current closure through the neutron star crust

Abstract

Force-free pulsar magnetospheres develop a large scale poloidal electric current circuit that flows along open magnetic field lines from the neutron star to the termination shock. The electric current closes through the interior of the neutron star where it provides the torque that spins-down the star. In the present work, we study the internal electric current in an axisymmetric rotator. We evaluate the path of the electric current by requiring the minimization of internal Ohmic losses. We find that, in millisecond pulsars, the current reaches the base of the crust, while in pulsars with periods of a few seconds, the bulk of the electric current does not penetrate deeper than about $100$ m. The region of maximum spin-down torque in millisecond pulsars is the base of the crust, while in slowly spinning ones it is the outer crust. We evaluate the corresponding Maxwell stresses and find that, in typical rotation-powered radio pulsars, they are well below the critical stress that can be sustained by the crust. For magnetar-level fields, the Maxwell stresses near the surface are comparable to the critical stress and may lead to the decoupling of the crust from the rest of the stellar rotation.

10 pages, 6 Figures, Accepted by MNRAS

References in corpus (7)

• Untwisting magnetospheres of neutron stars
• Disordered nuclear pasta, magnetic field decay, and crust cooling in neutron stars
• The Prelude to and Aftermath of the Giant Flare of 2004 December 27: Persistent and Pulsed X-ray Properties of SGR 1806-20 from 1993 to 2005
• Pulsar braking and the P-Pdot diagram
• Magnetic-field evolution in a plastically-failing neutron-star crust
• Magnetic Axis Drift and Magnetic Spot Formation in Neutron Stars with Toroidal Fields
• On the role of the current loss in radio pulsar evolution