arXiv subjects

K. P. Levenfish

Publications and source records attributed to K. P. Levenfish.

23 records · Page 2Linked to original sources

arXiv2000

Bulk viscosity in superfluid neutron star cores. I. Direct Urca processes in npeμmatter

The bulk viscosity of the neutron star matter due to the direct Urca processes involving nucleons, electrons and muons is studied taking into account possible superfluidity of nucleons in the neutron star cores. The cases of singlet-state pairing or triplet-state pairing (without and with nodes of the superfluid gap at the Fermi surface) of nucleons are considered. It is shown that the superfluidity may strongly reduce the bulk viscosity. The practical expressions for the superfluid reduction factors are obtained. For illustration, the bulk viscosity is calculated for two models of dense matter composed of neutrons, protons,electrons and muons. The presence of muons affects the bulk viscosity due to the direct Urca reactions involving electrons and produces additional comparable contribution due to the direct Urca reactions involving muons. The results can be useful for studying damping of vibrations of neutron stars with superfluid cores.

astro-ph↗

arXiv1999

Cooling neutron stars and superfluidity in their interiors

We study the heat capacity and neutrino emission reactions (direct and modified Urca processes, nucleon-nucleon bremsstrahlung, Cooper pairing of nucleons) in matter of supranuclear density of the neutron star cores with superfluid neutrons and protons. Various superfluidity types are analysed (singlet-state pairing and two types of triplet-state pairing, without and with nodes of the gap at a nucleon Fermi surface). The results are used for cooling simulations of isolated neutron stars. Both, the standard cooling and the cooling enhanced by the direct Urca process, are strongly affected by nucleon superfluidity. Comparison of cooling theory of isolated neutron stars with observations of their thermal radiation may give stringent constraints on the critical temperatures of the neutron and proton superfluidities in the neutron star cores.

astro-ph↗

arXiv1999

A simple model of cooling neutron stars with superfluid cores: comparison with observations

Cooling of neutron stars (NSs) with superfluid cores is simulated taking into account neutrino emission produced by Cooper pairing of nucleons. The critical temperatures of neutron and proton superfluidities, $T_{cn}$ and $T_{cp}$, are assumed to be constant over the NS core, and treated as free parameters. They are constrained using the surface temperatures $T_s$ of isolated NSs (RX J0822-43, PSR 1055-52, 1E 1207-52, Vela, Geminga, PSR 0656+14, RX J0002+62), obtained by interpretation of observed thermal radiation either with black body spectrum or with hydrogen atmosphere models.

astro-ph↗

arXiv1998

Neutrino emission due to Cooper pairing of nucleons in cooling neutron stars

The neutrino energy emission rate due to formation of Cooper pairs of neutrons and protons in the superfluid cores of neutron stars is studied. The cases of singlet-state pairing with isotropic superfluid gap and triplet-state pairing with anisotropic gap are analysed. The neutrino emission due to singlet-state pairing of protons is found to be greatly suppressed with respect to the cases of singlet- and triplet-state pairings of neutrons. The neutrino emission due to pairing of neutrons is shown to be very important in the superfluid neutron-star cores with the standard neutrino luminosity and with the luminosity enhanced by the direct Urca process. It can greatly accelerate both, standard and enhanced, cooling of neutron stars with superfluid cores. This enables one to interpret the data on surface temperatures of six neutron stars, obtained by fitting the observed spectra with the hydrogen atmosphere models, by the standard cooling with moderate nucleon superfluidity.

astro-ph↗

arXiv1996

Standard and Enhanced Cooling of Neutron Stars with Superfluid Cores

Calculations are performed of the cooling of neutron stars with standard and enhanced neutrino energy losses in the presence of neutron and proton superfluidities in the stellar cores. The effects of superfluidity on the heat capacity and the neutrino luminosity produced by the direct and modified Urca processes and by the neutrino bremsstrahlung emission in nucleon-nucleon collisions are taken into account. The constraints are analyzed on the critical temperatures $\tn$ and $\tp$ of the transition of neutrons and protons to the superfluid state, which can be obtained from a comparison of observational data on thermal radiation from neutron stars with theoretical cooling curves for the standard and enhanced neutrino energy losses. Possible ranges of $\tn$ and $\tp$ for the pulsar Geminga are discussed.

astro-ph↗