Enhanced cooling of neutron stars via Cooper-pairing neutrino emission

We simulate cooling of superfluid neutron stars with nucleon cores where the direct Urca process is forbidden. We adopt density-dependent critical temperatures T-cp(rho) and T-cn(rho) of singlet-state proton and triplet-state neutron pairing in a stellar core and consider strong proton pairing (with maximum T-cp(max) greater than or similar to 5 x 10(9) K) and moderate neutron pairing (T-cn(max) similar to 6 x 10(8) K). When the internal stellar temperature T falls below T-cn(max), the neutrino luminosity L-CP due to Cooper pairing of neutrons behaves proportional toT(8), 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-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.