Neutron stars provide natural astrophysical laboratories for probing the properties of superdense matter. Modeling the cooling of neutron stars is one of the potential methods of investigating the structure of neutron stars. Neutrino emissivity of a neutron star is of a great physical interest since it is one of the most important physical inputs to solve two equations: the thermal balance equation and the thermal transport equation, which are used to get the cooling curves of neutron stars.

Researchers in Theoretical Physics Group at Institute of Modern Physics, Chinese Academy of Sciences (IMP) investigated the three-body force (TBF) effect on the neutrino emissivity in neutron star matter and the total neutrino emissivity of neutron stars within the framework of the Brueckner-Hartree-Fock approach by adopting the AV18 two-body interaction plus a microscopic TBF.

Results showed that TBF effect reduced remarkably the density thresholds of the direct Urca (DU) processes involving electrons and muons from 0.67 fm^-3 and 0.76fm^-3 to 0.38fm^-3 and 0.42fm^-3 , respectively.

Furthermore, it was found that inclusion of TBF enhanced strongly the neutrino emissivity in the density region of 0 .38fm^-3<n<0.67fm^-3 in β-stable neutron star matter. In other density region, TBF effect on the neutrino emissivity turned out to be quite small.

In addition, researchers found that the total neutrino emissivity from a neutron star increased as its mass increases. For neutron stars with relatively small masses, TBF effect on the total neutrino emissivity was proved to be negligibly small. TBF effect on the total neutrino emissivity was visible for neutron stars with relatively large masses. However, it was not as strong as expected, and inclusion of TBF enhanced the total neutrino emissivity by only about 50% for neutron stars with a given mass of 1.6M_⊙.

The work has been published inPhys. Rev. C88 (2013) 015804.

Fig.1 Density dependence of the neutrino emissivity in npeμ neutron star matter at three different temperatures, i.e.,　 (Image by IMP)

Fig. 2 Total neutrino emissivity of neutron stars. (Image by IMP)