Enhanced cooling of neutron stars via Cooper-pairing neutrino emission

• Published in: Astronomy and astrophysics (Berlin) 2004-09, Vol.423 (3), p.1063-1071
• Main Authors: Gusakov, M. E., Kaminker, A. D., Yakovlev, D. G., Gnedin, O. Y.
• Format: Article
• Language: English
• Subjects: dense matter; stars: neutron
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20041006

We simulate cooling of superfluid neutron stars with nucleon cores where the direct Urca process is forbidden. We adopt density-dependent critical temperatures $T_{\rm cp}(\rho)$ and $T_{\rm cn}(\rho)$ of singlet-state proton and triplet-state neutron pairing in a stellar core and consider strong proton pairing (with maximum $T_{\rm cp}^{\rm max} \ga 5 \times 10^9$ K) and moderate neutron pairing ($T_{\rm cn}^{\rm max} \sim 6 \times 10^8$ K). When the internal stellar temperature T falls below $T_{\rm cn}^{\rm max}$, the neutrino luminosity LCP due to Cooper pairing of neutrons behaves $\propto$ T8, just as that produced by the modified Urca process (in a non-superfluid star) but is higher by about two orders of magnitude. In this case the Cooper-pairing neutrino emission acts like an enhanced cooling agent. By tuning the density dependence $T_{\rm cn}(\rho)$ we can explain observations of cooling isolated neutron stars in the scenario in which the direct Urca process or a similar process in kaon/pion condensed or quark matter are absent.