COOLING AND DETECTABILITY OF NEUTRON STARS

Abstract

Surface properties, temperature effects, cooling behavior, and observability of neutron stars have been studied. For this purpose, the opacity of the surface layers is calculated both for a pure iron and a pure magnesium composition. It is found that the nondegenerate layers are only a few meters thick and in no case exceed 1% of the stellar radius. The star cools mainly through neutrino emission when [Formula: see text], but at lower temperatures the cooling is primarily through electromagnetic radiation. The neutrino cooling mechanisms included were the neutrino plasma process, the URCA process, and the neutrino bremsstrahlung process. The cooling behavior is quite complicated, with the rate of cooling generally depending on mass, nuclear potential, and surface composition, among which the dependence on mass is the most significant. It will be hard to observe low-mass neutron stars because of fast cooling rates. However, medium-and high-mass stars should still have temperatures exceeding about 2 × 106 °K on the surface for times of the order of 103 to 105 years. Hence, it should not be impossible to observe massive neutron stars relatively close to us, if there is no X-ray emission of larger flux coming from the surrounding region.