Enhanced cooling of neutron stars via Cooper-pairing neutrino emission

¹ Ioffe Physical Technical Institute, Politekhnicheskaya 26, 194021 St. Petersburg, Russia e-mail: [gusakov;kam;yak]@astro.ioffe.ru
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA e-mail: ognedin@stsci.edu

Received: 1 April 2004
Accepted: 2 May 2004

Abstract

We simulate cooling of superfluid neutron stars with nucleon cores where the direct Urca process is forbidden. We adopt density-dependent critical temperatures and of singlet-state proton and triplet-state neutron pairing in a stellar core and consider strong proton pairing (with maximum  K) and moderate neutron pairing ( K). When the internal stellar temperature T falls below , the neutrino luminosity L_CP due to Cooper pairing of neutrons behaves 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 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.