Neutron star cooling is a hot topic that connects nuclear physics and astrophysics. The observations combined with theory of neutron star (NS) cooling play a crucial role in achieving the intriguing information of the stellar interior, such as the equation of state, composition, and superfluidity of dense matter. The traditional NS cooling theory is based on the assumption that the stellar structure does not change with time. The validity of such a static description has not yet been confirmed.
The researchers in the Institute of Modern Physics (IMP), Chinese Academy of Sciences，have investigated the neutron star cooling affected by the Dynamic Stellar Structure. We generalize the theory to a dynamic treatment; that is, continuous change of the NS structure (rearrangement of the stellar density distribution with the total baryon number fixed) as the decrease of temperature during the thermal evolution, is taken into account. It is found that the practical thermal energy used for the cooling is slightly lower than that estimated in a static situation, as ahown in Fig. 1, and hence the cooling of NSs is accelerated correspondingly but the effect is rather weak. Therefore, the static treatment is usually a good approximation in the calculations of NS Cooling for canonial NSs. But for large mass stars, one may take into account the dynamic treatment. Therefore, our work not only examines whether the traditional static description of cooling is valid or not, but also deepens our understanding of the NS cooling.
The work is supported by the Youth Innovation Promotion Association of Chinese Academy of Sciences, National Natural Science Foundation of China, the 973 Program of China, and has been published in Astrophysical Journal, 862，67 (2018).
Fig. 1 the dynamic and static thermal energy (and their ratio η) as a function of neutron star mass.