The Nucleon Direct Urca Processes in a Cooling Neutron Star

Abstract

In the relativistic mean field approximation, the relativistic energy losses of the nucleon direct Urca processes are studied in the degenerate baryon matter of neutron stars. We investigate the effects of hyperon degrees of freedom and the isovector scalar interaction which is considered by exchanging 𝛿 meson on the nucleon direct Urca processes in neutron star matter. The results indicate that the existence of hyperons decreases the abundance of protons and leptons and can sharply suppress the neutrino emissivity of the nucleon direct Urca processes, while it has only a little influence on the neutrino luminosity for a fixed neutron star whether 𝛿 mesons appear in a neutron star or not. However, the presence of 𝛿 mesons can result in obvious growth in the neutrino emissivity and luminosity which will speed up the cooling rate for the nonsuperfluid neutron star.

Neutrino emissivity of the nucleon direct URCA process for rotational traditional and hyperonic neutron stars

“…When the density is larger than 2-3 times the saturation density, hyperons appear in the neutron stars [6]. References [7][8][9][10][11] have studied the effects of hyperons on the N-DURCA process and suggested that the existence of hyperons can reduce the neutrino emissivity of the N-DURCA process. The hyperon direct URCA process also exists once the Λ hyperon appears [12].…”

Direct Urca processes involving singlet proton superfluidity in neutron star cooling

“…Among them, the most powerful enhancement of neutrino emission is provided by the nucleon direct Urca processes (NDUP), secondarily is the hyperon direct Urca processes (HDUP) [21][22][23][24][25][26][27][28]. Besides, the degrees of freedom of hyperons tend to soften the equation of state (EOS) calculated in the relativistic mean field (RMF) model based on SU (6) spin-flavor symmetry(quark model for the vector meson-hyperon coupling constants), then reduce the maximum mass of NS to about 1.6-1.7M ⊙ [29][30][31][32][33][34][35]. However, Demorest et al in 2010 [36] indicated that the binary millisecond pulsar PSR J1614-2230 expanded the maximum observational mass from 1.67 ± 0.02M ⊙ to 1.97 ± 0.04M ⊙ using the Shapiro delay measurements from radio timing observations.…”

Singlet S-wave superfluidity of proton in neutron star matter

“…In recent years, many studies have been focussing on 1 S 0 protonic superfluidity. Since the protonic superfluid states as well as their pairing strength can greatly suppress the neutrino processes involving nucleons about 10 5 − 10 6 years of NS cooling phases, affect the properties of rotating dynamics, post-glitch timing observations and possible vertex pinning of NSs [14][15][16][17][18][19][20][21][22].…”