The relevance of ambipolar diffusion for neutron star evolution

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We study ambipolar diffusion in strongly magnetised neutron stars, with special focus on the effects of neutrino reaction rates and the impact of a superfluid/superconducting transition in the neutron star core.

• For axisymmetric magnetic field configurations, we determine the deviation from $\beta-$equilibrium induced by the magnetic force and calculate the velocity of the slow, quasi-stationary, ambipolar drift.
• We study the temperature dependence of the velocity pattern and clearly identify the transition to a predominantly solenoidal flow.
• For stars without superconducting/superfluid constituents and with a mixed poloidal-toroidal magnetic field of typical magnetar strength, we find that ambipolar diffusion proceeds fast enough to have a significant impact on the magnetic field evolution only at low core temperatures, $T \lesssim 1-2\times10^8$ K.