We present solutions for Hall equilibria applicable to neutron star crusts. Such magnetic configurations satisfy a Grad-Shafranov-type equation, which is solved analytically and numerically. The solutions presented cover a variety of configurations,
from purely poloidal fields connected to an external dipole to poloidal-toroidal fields connected to an external vacuum field, or fully confined within the star. We find that a dipole external field should be supported by a uniformly rotating electron fluid. The energy of the toroidal magnetic field is generally found to be a few percent of the total magnetic field energy for the fields with an external component. We discuss the evolution due to Ohmic dissipation which leads to slowing down of the electron fluid. We also find that the transition from an MHD equilibrium to a state governed by Hall effect, generates spontaneously an additional toroidal field in regions where the electron fraction changes.
We study semi-analytical time-dependent solutions of the relativistic magnetohydrodynamic (MHD) equations for the fields and the fluid emerging from a spherical source. We assume uniform expansion of the field and the fluid and a polytropic relation
between the density and the pressure of the fluid. The expansion velocity is small near the base but approaches the speed of light at the light sphere where the flux terminates. We find self-consistent solutions for the density and the magnetic flux. The details of the solution depend on the ratio of the toroidal and the poloidal magnetic field, the ratio of the energy carried by the fluid and the electromagnetic field and the maximum velocity it reaches.
