We have considered the neutrino emission produced by the direct Urca process in the cores of neutron stars with strong magnetic fields. We have derived the general expression for the neutrino emissivity [Eqs. (5) and (7)], and analysed it (Sect. 3) in the most important case, in which the magnetic field is not too strong, and the reacting electrons and protons populate many Landau levels. We have shown that the magnetic field can switch on the direct Urca process under the conditions, in which the field-free process is strongly suppressed by momentum conservation. We have obtained the analytical fit expressions (22) and (23) for this enhanced emissivity. We have performed a series of neutron star cooling simulations for the model, in which the star has a strong neutron superfluidity in the outer core but no superfluidity in the inner core. We have demonstrated, that the magnetic fields G in the stellar center can strongly enhance the neutrino luminosity and accelerate the cooling of neutron stars with masses by about 10% below the threshold mass, minimum mass of a star at which the field-free direct Urca process starts to be permitted. Therefore, the cooling can be controlled by the central stellar magnetic fields. The effect does not require superstrong fields G analysed by different authors.
© European Southern Observatory (ESO) 1999
Online publication: December 22, 1998