We study the long-term heating due to magnetic field decay in the core of neutron star. Two cases for the nucleonic core are considered: normal and strongly superconducting. We give simple scaling ...relations (depending on the internal stellar temperature and the averaged magnetic field in the core) to estimate the magnetic field decay rate for the most important dissipation processes. Comparison to properties of observed neutron stars suggests that heating due to the magnetic field decay is (at least partially) responsible for the thermal states of middle-aged magnetars and highly-magnetized isolated neutron stars with ages of 1 — 10 Myr.
We show that the r-modes of slowly rotating nonbarotropic neutron stars are described by nonanalytic functions of stellar angular velocity, which makes the perturbation techniques, used so far in the ...r-mode theoretical studies, inapplicable. In contrast to those studies and in accordance with numerical calculations beyond the slow rotation approximation, the obtained r-mode spectrum is discrete, which resolves the continuous spectrum problem, lasting since 1997. Our findings imply that the relativistic r-modes in slowly rotating neutron stars dramatically differ from their Newtonian cousins, which may have important implications for the detectability of r-mode signatures in observations, in particular for the r-mode excitation efficiency during the neutron star inspirals.
We calculate the important quantity of superfluid hydrodynamics, the relativistic entrainment matrix for a nucleon-hyperon mixture at arbitrary temperature. In the nonrelativistic limit this matrix ...is also termed the Andreev-Bashkin or mass-density matrix. Our results can be useful for modeling the pulsations of massive neutron stars with superfluid nucleon-hyperon cores and for studies of the kinetic properties of superfluid baryon matter.
In a previous paper M. E. Gusakov, A. I. Chugunov, and E. M. Kantor, Phys. Rev. Lett. 112, 151101 (2014), we introduced a new scenario that explains the existence of rapidly rotating warm neutron ...stars (NSs) observed in low-mass x-ray binaries (LMXBs). Here it is described in more detail. The scenario takes into account the interaction between superfluid inertial modes and the normal (quadrupole) m = 2 r mode, which can be driven unstable by the Chandrasekhar-Friedman-Schutz (CFS) mechanism. This interaction can only occur at some fixed "resonance" stellar temperatures; it leads to formation of the "stability peaks" which stabilize a star in the vicinity of these temperatures. We demonstrate that a NS in LMXB spends a substantial fraction of time on the stability peak, that is, in the region of stellar temperatures and spin frequencies that has been previously thought to be CFS unstable with respect to excitation of r modes. We also find that the spin frequencies of NSs are limited by the CFS instability of normal (octupole) m = 3 r mode rather than by m = 2 r mode. This result agrees with the predicted value of the cutoff spin frequency ~ 730 Hz in the spin distribution of accreting millisecond x-ray pulsars. In addition, we analyze evolution of a NS after the end of the accretion phase and demonstrate that millisecond pulsars can be born in LMXBs within our scenario. Besides millisecond pulsars, our scenario also predicts a new class of LMXB descendants-hot and rapidly rotating nonaccreting NSs ("hot widows"/HOFNARs). Further comparison of the proposed theory with observations of rotating NSs can impose new important constraints on the properties of superdense matter.
Observations of accreting neutron stars are widely used to constrain the microphysical properties of superdense matter. A key ingredient in this analysis is the heating associated with nuclear ...reactions in the outer layers of the neutron star (crust), as well as the equation of state and composition of these layers. As recently shown, the neutron hydrostatic/diffusion (nHD) condition is valid in the inner part of the crust, where some of the neutrons are not bound to the nuclei, and this condition should be properly incorporated into crustal models. Here we construct models of the accreted crust of a neutron star, taking into account the nHD condition and proton shell effects in nuclei. For numerical illustration, we employ the recently proposed compressible liquid drop model, which incorporates shell effects. However, our approach is general and can also be used in future studies relying on more sophisticated nuclear physics models.
With neutron star applications in mind, we developed a theory of diffusion in mixtures of superfluid, strongly interacting Fermi liquids. By employing the Landau theory of Fermi liquids, we ...determined matrices that relate the currents of different particle species, their momentum densities, and the partial entropy currents to each other. Using these results, and applying the quasiclassical kinetic equation for the Bogoliubov excitations, we derived general expressions for the diffusion coefficients, which properly incorporate all the Fermi liquid effects and depend on the momentum transfer rates between different particle species. The developed framework can be used as a starting point for systematic calculations of the diffusion coefficients (as well as other kinetic coefficients) in superfluid Fermi mixtures, particularly, in superfluid neutron stars.
It is commonly believed that the dissipative properties of superdense matter play a negligible role in modeling gravitational waveforms from neutron star inspirals. This study aims to investigate ...whether this presumption holds true for the often neglected dissipative process associated with particle diffusion in superconducting neutron stars. As we demonstrate, diffusion effects can significantly impact the phase of the gravitational wave from the inspiral, manifesting at a magnitude of a few tens of milliradians at large orbit separations, equivalent to orbital frequencies of a few hertz. We also find that dissipation resulting from particle diffusion might increase the neutron star's temperature to approximately \(10^7\rm K\) during the inspiral.
MNRAS, 485, 4936-4950 (2019) Force on proton vortices in superfluid and superconducting matter of neutron
stars is calculated at vanishing stellar temperature. Both longitudinal
(dissipative) and ...transverse (Lorentz-type) components of the force are derived
in a coherent way and compared in detail with the corresponding expressions
available in the literature. This allows us to resolve a controversy about the
form of the Lorentz-type force component acting on proton vortices. The
calculated force is a key ingredient in magnetohydrodynamics of superconducting
neutron stars and is important for modeling the evolution of stellar magnetic
field.
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