Quasistationary fluid motions in magnetized neutron stars

In the recent work by Gusakov, Kantor & Ofengeim [Phys. Rev. D 96, 103012 (2017)] a new method to calculate the quasistationary evolution of magnetic field in the core of a neutron star was proposed. Here we further develop it, focusing on a simple case of neutron-proton-electron (npe) core composition with purely poloidal magnetic field B. We find that the meridional flow of the npe-fluid can be unexpectedly large. We estimate the typical timescale τ of the field evolution due to dragging of the magnetic field lines by this flow and show that τ can be as small as ∼ (100 — 1000) yr for magnetars with B ∼ 10¹⁶ G. (paper)