Kostas Glampedakis, Nils Andersson, Ian Jones, Lars Samuelsson
One of the main mechanisms driving magnetic field evolution in the interior of neutron stars is the so-called magnetic ambipolar diffusion; this is based on the notion of a slow relative drift between the charged and neutral fluid components of the star. Our recent paper (Glampedakis, Jones & Samuelsson, 2011) provides a revision of earlier work on the subject by considering the more realistic case of superfluid neutron stars. The key result of our work is that proton superconductivity and/or neutron superfluidity leads to significantly longer magnetic field evolution timescales due to ambipolar diffusion. This is an indication that the commonly accepted model of magnetic field evolution in magnetars may need partial revision.
This is one of the scopes of our second paper on the subject (Glampedakis & Andersson, 2011). In that work we have considered an entirely different mechanism for magnetic field evolution, based on the likely strong interaction ("pinning") between the quantized neutron vortices and proton fluxtubes which make part of the interior superfluids in neutron stars. We have found that such an interaction is likely to be persistent in magnetars, leading to magnetic field evolution timescales that could be comparable to the estimated ages of these objects and, therefore, of potential astrophysical importance. At the same time we have found that less magnetized neutron stars such as young pulsars and old, rapidly spinning systems do not allow any long-term vortex-fluxtube pinning in their superfluid cores. Hence this mechanism is unlikely to be responsible for magnetic field evolution in these objects.
Glampedakis, K. & Andersson, N. (2011). Magneto-rotational Neutron Star Evolution: The Role of Core Vortex Pinning. ApJL, 740, L35.
Glampedakis, K., Jones, D.I. & Samuelsson, L. (2011). Ambipolar diffusion in superfluid neutron stars. M.N.R.A.S., 413, 2021.