Incompatibility of long-period neutron star precession with creeping neutron vortices

Dipartimento di Fisica “Enrico Fermi”, Università di Pisa, Largo Pontecorvo 3, Pisa, 56127 Italy e-mail: link@physics.montana.edu

Received: 23 May 2006
Accepted: 1 August 2006

Abstract

Aims.To determine whether “vortex creep” in neutron stars, the slow motion of neutron vortices with respect to pinning sites in the core or inner crust, is consistent with observations of long-period precession.

Methods.Using the concept of vortex drag, I discuss the precession dynamics of a star with imperfectly-pinned (i.e., “creeping”) vortices.

Results.The precession frequency is far too high to be consistent with observations, indicating that the standard picture of the outer core (superfluid neutrons in co-existence with type II, superconducting protons) should be reconsidered. There is a slow precession mode, but it is highly over-damped and cannot complete even a single cycle. Moreover, the vortices of the inner crust must be able to move with little dissipation with respect to the solid.