MAGNETIC-FIELD EVOLUTION WITH HALL DRIFT IN NEUTRON-STARS

The role of the Hall current in plasma physics is studied in a model of neutron star magnetic fields. We calculate the evolution of the neutron star magnetic held with and without the Hall current effect. In our model, it is assumed that the magnetic field is confined to the crust and that the field dissipates through ohmic decay. The decay rates are expected to increase with the multipole moments if there is no Hall current and the dipole field is likely to survive. The presence of the Hall current causes coupling among the different modes, and the energy is transferred among them. We find that the dipole magnetic field does not always survive, and the decay features depend on the configuration of the fields. We speculate that some old neutron stars such as gamma-ray bursters may have strong, disordered-surface magnetic fields, but a weak dipole field.