On the magnetic field evolution in isolated neutron stars

We examine the discrepancy between the theoretically expected number of detectable isolated old neutron stars (10(2)-10(3)), and the actually detected number of candidates (2-3). We argue that this discrepancy is explicable in terms of the suppression of accretion from the interstellar medium onto the old neutron stars. We show that for such a suppression to occur, a specific pattern for the magnetic field evolution in neutron stars is required, Strong magnetic fields (B greater than or similar to 10(12) G) are required to decay rapidly, while fields of the order of 10(10) G are required to remain constant in the absence of accretion. The required pattern agrees with recent theoretical models for magnetic field decay in neutron stars.