73 research outputs found
Bulk viscosity in superfluid neutron star cores. III. Effects of hyperons
Bulk viscosity of neutron star cores containing hyperons is studied taking
into account non-equilibrium weak process .
Rapid growth of the bulk viscosity within the neutron star core associated with
switching on new reactions (modified Urca process, direct Urca process, hyperon
reactions) is analyzed. The suppression of the bulk viscosity by superfluidity
of baryons is considered and found out to be very important.Comment: LaTeX, 9 pages, added reference, version accepted by Astron.
Astrophy
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.Comment: LaTeX, 85 pages, 23 figures, Physics - Uspekhi (accepted
Bulk viscosity in superfluid neutron star cores. I. Direct Urca processes in npe\mu matter
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.Comment: 14 pages, 7 figures, latex, uses aa.cls, to be published in Astronomy
and Astrophysic
Adiabatic Index of Dense Matter and Damping of Neutron Star Pulsations
The adiabatic index Gamma_1 for perturbations of dense matter is studied under various physical conditions which can prevail in neutron star cores. The dependence of Gamma_1 on the composition of matter (in particular, on the presence of hyperons), on the stellar pulsation amplitude, and on the baryon superfluidity is analyzed. Timescales of damping of stellar pulsations are estimated at different compositions, temperatures, and pulsation amplitudes. Damping of pulsations by bulk viscosity in the neutron-star cores can prevent the stars to pulsate with relative amplitudes > (1-15)% (depending on the composition of matter)
Quark core impact on hybrid star cooling
In this paper we investigate the thermal evolution of hybrid stars, objects
composed of a quark matter core, enveloped by ordinary hadronic matter. Our
purpose is to investigate how important are the microscopic properties of the
quark core to the thermal evolution of the star. In order to do that we use a
simple MIT bag model for the quark core, and a relativistic mean field model
for the hadronic envelope. By choosing different values for the microscopic
parameters (bag constant, strange quark mass, strong coupling constant) we
obtain hybrid stars with different quark core properties. We also consider the
possibility of color superconductivity in the quark core. With this simple
approach, we have found a set of microscopic parameters that lead to a good
agreement with observed cooling neutron stars. Our results can be used to
obtain clues regarding the properties of the quark core in hybrid stars, and
can be used to refine more sophisticated models for the equation of state of
quark matter.Comment: 8 pages, 10 figures. Accepted for publication in Physical Review
Thermal Evolution and Light Curves of Young Bare Strange Stars
The cooling of a young bare strange star is studied numerically by solving
the equations of energy conservation and heat transport for both normal and
superconducting strange quark matter inside the star. We show that the thermal
luminosity from the strange star surface, due to both photon emission and e+e-
pair production, may be orders of magnitude higher than the Eddington limit,
for about one day for normal quark matter but possibly for up to a hundred
years for superconducting quark matter, while the maximum of the photon
spectrum is in hard X-rays with a mean energy of ~ 100 keV or even more. This
differs both qualitatively and quantitatively from the photon emission from
young neutron stars and provides a definite observational signature for bare
strange stars. It is shown that the energy gap of superconducting strange quark
matter may be estimated from the light curves if it is in the range from ~ 0.5
MeV to a few MeV.Comment: Ref [10] added and abstract shortened. 4 pages, 3 figures, revtex4.
To be published in Phys. Rev. Letter
- …