Thermal Evolution of Isolated Neutron Stars: Pairing, Pairing, and Pairing

Abstract

The thermal evolution of young isolated neutron stars is driven by neutrino emission from matter at the highest densities reached in their inner core. As such, these objects are direct probes of the structure of matter at supranuclear density. However, pairing of the neutrino emitting baryons, or quarks, can significantly alter their emission efficiency and the predicted thermal evolution is very sensitive to assumptions about gap size(s). After a brief description of these physical processes, I compare with present observational data models of cooling neutron stars driven by slow or fast neutrino emission. Depending on the assumed size of the neutron 3P2−3F2 gap, a minimal model of neutron stars can accommodate all present data, with the exception of the cold pulsar J0007.0+7303 in the supernova remnant CTA 1. However, in case this gap is vanishingly small or very large, the estimated surface temperatures of more than a half of the observed young cooling neutron stars would imply the intervention of some form of enhanced neutrino emission. Unfortunately, the present uncertainty on the size of the neutron 3P2−3F2 gap precludes us to draw any definitive conclusion about the state of dense matter from the sole study of isolated neutron stars.