Nuclear Equation of State and Neutron Star Cooling

Yeunhwan Lim, Chang Ho Hyun, Chang-Hwan Lee

Published 2015-01-19Version 1

We investigate the effects of the nuclear equation of state (EoS) to the neutron star cooling. New era for nuclear EoS has begun after the discovery of $\sim 2\msun$ neutron stars PSR J1614$-$2230 and PSR J0348$+$0432 [1, 2]. Also recent works on the mass and radius of neutron stars from low-mass X-ray binaries [3] strongly constrain the EoS of nuclear matter. On the other hand, observations of the neutron star in Cassiopeia A (Cas A) more than 10 years confirmed the existence of nuclear superfluidity [4, 5]. Nuclear superfluidity reduces the heat capacities as well as neutrino emissivities. With nuclear superfluidity the neutrino emission processes are highly suppressed, and the existence of superfluidity makes the cooling path quite different from that of the standard cooling process. Superfluidity also allows new neutrino emission process, which is called `Pair Breaking and Formation'(PBF). PBF is a fast cooling process and can explain the fast cooling rate of neutron star in Cas A. Therefore, it is essential to add the superfluidity effect in the neutron star cooling process. In this work, we simulate neutron star cooling curves using both non-relativistic and relativistic nuclear models. The existence of too early direct Urca process shows that some of nuclear models do not fit for the cooling simulation. After this first selection process, the nuclear pairing gaps are searched using the observational neutron star's age and temperature data.