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1.
Both relativistic and non-relativistic two-fluid models of neutron star cores are constructed, using the constrained variational formalism developed by Brandon Carter and co-workers. We consider a mixture of superfluid neutrons and superconducting protons at zero temperature, taking into account mutual entrainment effects. Leptons, which affect the interior composition of the neutron star and contribute to the pressure, are also included. We provide the analytic expression of the Lagrangian density of the system, the so-called master function, from which the dynamical equations can be obtained. All the microscopic parameters of the models are calculated consistently using the non-relativistic nuclear energy density functional theory. For comparison, we have also considered relativistic mean field models. The correspondence between relativistic and non-relativistic hydrodynamical models is discussed in the framework of the recently developed 4D covariant formalism of Newtonian multifluid hydrodynamics. We have shown that entrainment effects can be interpreted in terms of dynamical effective masses that are larger in the relativistic case than in the Newtonian case. With the nuclear models considered in this work, we have found that the neutron relativistic effective mass is even greater than the bare neutron mass in the liquid core of neutron stars.  相似文献   

2.
The effect of proton superconductivity on the generation of a toroidal magnetic field inside a neutron star is examined. It is shown that including the entrainment of superconducting protons by superfluid neutrons does not change the previously obtained results. Proton superconductivity does influence the structure of the generated magnetic field since, over a time on the order of 104–105 years, the magnetic field increases linearly with time and can exceed the first critical field for proton superconductivity. The distribution of the stationary toroidal magnetic field inside a neutron star is also found.  相似文献   

3.
Strong evidence that some neutron stars precess (nutate) with long periods (∼1 yr) challenges our current understanding of the neutron star interior. I describe how neutron star precession can be used to constrain the state of the interior in a new way. I argue that the standard picture of the outer core, in which superfluid neutrons coexist with type II, superconducting protons, requires revision. One possible resolution is that the protons are not type II, but type I. Another possibility is that the neutrons are normal in the outer core. I conclude with a brief discussion of the implications for detectable gravitational wave emission from millisecond pulsars. Much of the work described here was supported by the National Science Foundation under Grant AST-00098728.  相似文献   

4.
The composition of neutron star atmospheres is calculated as a function of time including effects of diffusion, cooling and thermonuclear reactions. A seven-component nuclear reaction network with includes He4, C12, O16, Ne20, Mg24, Si28 and Fe56 is utilized. Neutron star models with different initial nuclear abundances are compared as to subsequent nucleosynthesis. It is found that the final abundances are independent of original composition assuming He4 as the major initial constituent. The final composition of the atmosphere is predominantly Fe56. Mass loss from an evolving neutron star is examined as a possible source of cosmic rays. It is found that a neutron star contributes only Fe56 significantly to the cosmic-ray spectrum.  相似文献   

5.
We obtained a series of four observations of the isolated neutron star Geminga over an 18 month period using the Advanced Camera for Surveys (ACS) Wide Field Camera (WFC) on the Hubble Space Telescope in order to determine its trigonometric parallax. We find the parallax π=4.0±1.3 mas, corresponding to a distance to Geminga of 250 ?62 +120  pc, a result 60% larger than the previously published value. The proper motion is 178.2±1.8 mas/year. In this paper, we describe the analysis techniques in detail since the amplitude of the parallactic shift is smaller than the camera’s pixel size. We fit each star in the images with an appropriate effective PSF and applied a distortion correction to generate stellar positions accurate to 0.01 pixels (～0.5 mas). The 134 stars common to all images serve to establish a reference frame for alignment of the image series. Our observations were made around the times of maximum parallactic shift. We discuss the implications of this new distance measurement for the inferred radius of Geminga, and the neutron star equation of state.  相似文献   

6.
We discuss the nature of the various modes of pulsation of superfluid neutron stars using comparatively simple Newtonian models and the Cowling approximation. The matter in these stars is described in terms of a two-fluid model, where one fluid is the neutron superfluid, which is believed to exist in the core and inner crust of mature neutron stars, and the other fluid represents a conglomerate of all other constituents (crust nuclei, protons, electrons, etc.). In our model, we incorporate the non-dissipative interaction known as the entrainment effect, whereby the momentum of one constituent (e.g. the neutrons) carries along part of the mass of the other constituent. We show that there is no independent set of pulsating g-modes in a non-rotating superfluid neutron star core, even though the linearized superfluid equations contain a well-defined (and real-valued) analogue to the so-called Brunt–Väisälä frequency. Instead, what we find are two sets of spheroidal perturbations whose nature is predominately acoustic. In addition, an analysis of the zero-frequency subspace (i.e. the space of time-independent perturbations) reveals two sets of degenerate spheroidal perturbations, which we interpret to be the missing g-modes, and two sets of toroidal perturbations. We anticipate that the degeneracy of all these zero-frequency modes will be broken by the Coriolis force in the case of rotating stars. To illustrate this we consider the toroidal pulsation modes of a slowly rotating superfluid star. This analysis shows that the superfluid equations support a new class of r-modes, in addition to those familiar from, for example, geophysical fluid dynamics. Finally, the role of the entrainment effect on the superfluid mode frequencies is shown explicitly via solutions to dispersion relations that follow from a 'local' analysis of the linearized superfluid equations.  相似文献   

7.
With the assumption, the physical 3-spacet = constant in a superdense star is spheroidal and the matter-density on the boundary surface of the configurationa = 2 × 1014 g cm–3( the average matter density in a neutron star) Vaidya and Tikekar (1982) proposed an exact relativistic model for a neutron star. They suggested that their model can describe the hydrostatic equilibrium conditions in such a superdense star with densities in the range of 1014-1016 g cm–3. Based on this model Parui and Sarma (1991) estimated the maximum limit of the density variation parameter for a stable neutron star (both for charged and uncharged) which is equal to 0.68, i.e. max = 0.68.In this paper we have shown variation of central density per unit equilibrium radius (0/a), variation of mass, upper limit of density variation parameter both for charged and uncharged neutron stars at densities 1015 and 1016 g cm–3, respectively. We have obtained max = 0.68, i.e. the same as before. The important is that the duration of stability among the neutron star's constituents around max will be shorter and shorter at higher densities as we proceed near the centre of the neutron star. In case of a charged neutron star, once stability among the constituents has been established, then unstability appears gradually maintaining linear relation between change in central density per unit equilibrium radius and change in mass whereas in case of uncharged neutron star, linear relation does not maintain.  相似文献   

8.
In this paper we generalize Walecka's (1974) mean field model to include the case of all the baryons in the eightfold state. We discuss the effect of hyperons and the physical properties of cool neutron stars. A general theoretical result is given without presupposing the SU(3) symmetry, and numerical calculation was made on assuming the SU(3) symmetry. When ρ = 4.43(+14) g/cm3, hyperons begin to appear; their effect is to soften the equation of state by about 8%. We obtained the following values: maximum mass of a neutron star, 2.37 M; the corresponding radius, 11.1 km; rotational inertia, 4.3 (+45) g cm2; central density, 2.32 (+15) g/cm3.  相似文献   

9.
The production of X-rays and gamma-rays in bursts is believed to be due to the rapid burning of matter accreted onto a neutron star surface from its companion, most probably a giant star. The accreted matter consists mainly of hydrogen and helium and a very small amount of heavy elements. Due to the infall of matter, the temperature at the bottom layers is raised to a value of the order of 108 K. The neutron star surface density is>107 g cm–3. As hydrogen burning is a slow process under any temperature and density conditions, we consider the helium-burning reactions as the source of gamma-rays in the neutron star surface. Under high-density conditions the ordinary laboratory reaction rates should become modified. At high-density conditions, the strong screening effect due to the polarising cloud of electrons around the ions become important and enhances the reaction rates considerably. The helium-burning reactions are calculated under such conditions. The abundances of helium-burning products such as12C, 116O, and20Ne, etc., are computed. Under high-density and temperature conditions carbon is found to be more abundant than oxygen. Neon is completely absent in almost all the relevant physical conditions in which a strong screening effect is operative. It is suggested that explosive burning of accreted helium of 10–13 M will account for the observed energy of gamm-ray burst.  相似文献   

10.
We investigate the combined effect of neutron and proton superfluidities on the cooling of neutron stars whose cores consist of nucleons and electrons. We consider the singlet state paring of protons and the triplet pairing of neutrons in the cores of neutron stars. The critical superfluid temperatures T c are assumed to depend on the matter density. We study two types of neutron pairing with different components of the total angular momentum of a Cooper pair along the quantization axis (|m J |=0 or 2). Our calculations are compared with the observations of thermal emission from isolated neutron stars. We show that the observations can be interpreted by using two classes of superfluidity models: (1) strong proton superfluidity with a maximum critical temperature in the stellar core T c max ?4×109 K and weak neutron superfluidity of any type (T c max ?2×108 K); (2) strong neutron superfluidity (pairing with m J =0) and weak proton superfluidity. The two types of models reflect an approximate symmetry with respect to an interchange of the critical neutron and proton pairing temperatures.  相似文献   

11.
A static spherically-symmetric model, based on an exact solution of Einstein's equation, gives the permissible matter density 2×1014 g cm–3. If we use the change in the ratio of central density to the radiusr=a (i.e., central density per unit radius (0/a), we call it radius density) minimum, we have estimated the upper limit of the density variation parameter () and minimum mass limit of a superdense star like a neutron star. This limit gives an idea of the domain where the neutron abundance with negligible number of electrons and protons (may be treated as pure neutrons) and equilibrium in neutrons begins.  相似文献   

12.
We describe the cooling theory for isolated neutron stars that are several tens of years old. Their cooling differs greatly from the cooling of older stars that has been well studied in the literature. It is sensitive to the physics of the inner stellar crust and even to the thermal conductivity of the stellar core, which is never important at later cooling stages. The absence of observational evidence for the formation of a neutron star during the explosion of Supernova 1987A is consistent with the fact that the star was actually born there. It may still be hidden in the dense center of the supernova remnant. If, however, the star is not hidden, then it should have a low thermal luminosity (below ～1034 erg s?1) and a short internal thermal relaxation time (shorter than 13 yr). This requires that the star undergo intense neutrino cooling (e.g., via the direct Urca process) and have a thin crust with strong superfluidity of free neutrons and/or an anomalously high thermal conductivity.  相似文献   

13.
The final nuclear composition of the matter expanding from the density of a neutron star is investigated. It is assumed that starquakes cause the cracks which penetrate the neutron star crust and that the neutron star fluid can flow out through the cracks into space. The change with time of the nuclear composition of this matter is calculated by use of the compressible nuclear mass formula, and the hydrodynamics of the system is followed by the effect of nuclear transformation with time of the second fission of heavy neutron-rich nuclei, which is followed by a rapid rise to above 109 K. If the value of the -strength function exceeds about 10–5.5 MeV–1 s–1, the system proceeds to a state of nuclear equilibrium in the later expansion stage and the nuclear composition is reshuffled, finally to be transformed into neutron-excess, stable nuclei within the atomic mass region 80A120. It also becomes clear that if the strength function has a value smaller than the above critical value, then the neutron-rich nuclides withA[200, 400] are copiously produced. These results will also be applied in the cases of a neutron-star-black-hole collision and the explosion of a neutron star associated with the catastrophic phase transition within the neutron star core. The astrophysical implications are briefly discussed.  相似文献   

14.
Plasma density gradient which is inherent to degenerate neutron star matter is shown to lead to large scale plasma diffusion and subsequent charge separation. The surface (internal) fields generated by the spinning separated charges are found to be dipolar with intensities of ≃ 1014 G (for the surface fields) very early in the life-time of a typical neutron star. The internal fields, on the other hand, are relatively much weaker. These fields, which in this case are also shown to be temperature dependent, decay as a result of neutrino and photon emissions. The decay law derived from equations of standard cooling calculations and the equation connecting the magnetic field and temperature is indicated to have two distinct modes, each corresponding to the two branches of a typical neutron star cooling curve. We have found that results derived from the decay law are consistent with observational findings. Based on the theory behind our new model, we have also argued to show that isolated millisecond and sub-millisecond pulsars might be very rare objects. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

15.
In neutron star matter over the density range 4.3×1011<-ϱ≤4×1014 g cm−3 there are both free neutrons and neutron-rich nuclei. If there is a weak neutral current interaction between neutrinos and neutrons, as suggested by recent experiments, then when neutrons scatter off nuclei they may emit pairs as bremsstrahlung radiation. We calculate the associated emissivity for degenerate (but not superfluid) neutrons and uncorrelated (not crystallized) nuclei. We find that, under these conditions. this emissivity can under some conditions compare with that calculated by Festa and Ruderman for bremsstrahlung in electron-nucleus collisions.  相似文献   

16.
Many unidentified lines in the spectrum of Przybylski’s star (HD 101065) match well the spectral lines of radioactive elements, including the lines of short-lived isotopes. The origin of such isotopes in the atmosphere of the star remains unknown. We discuss a scenario in which some heavy nuclei of radioactive elements are produced in Przybylski’s star atmosphere as a result of its permanent exposure to the gamma flux (photon-nuclear reactions) or of the direct interaction of the free neutrons which arise in the atmosphere with seed nuclei of lighter elements (r-process). In both cases the gamma quanta and the free neutrons originate due to the presence of the neutron star which forms a close binary system with Przybylski’s star. This neutron star is the source of the fast electrons and positrons which produce gamma quanta when they are decelerated in their interaction with the atomic nuclei of the atmospheric plasma, while free neutrons can originate in the reactions of the direct capture of fast electrons by atmospheric protons (nuclei of hydrogen atoms).  相似文献   

17.
The model of a magnetized rotating neutron star with an electric current in the region of its fluid polar magnetic caps is considered. The presence of an electric current leads to differential rotation of the magnetic caps. The rotation structure is determined by the electric current density distribution over the surface. In the simplest axisymmetric configuration, the current flows in one direction near the polar cap center and in the opposite direction in the outer ring (the total current is zero for the neutron star charge conservation). In this case, two rings with opposite directions of rotation appear on the neutron star surface, with the inner ring always lagging behind the star’s main rotation. The differential rotation velocity is directly proportional to the electric current density gradient along the polar cap radius. At a width of the region of change in the electric current from 1 to 102 cm and a period ～1 s and a magnetic field B ～ 1012 G typical of radio pulsars, the linear differential rotation velocity is ～10?2–10?4 cm s?1 (corresponding to a revolution time of ～0.1–10 yr).  相似文献   

18.
We examine a possible manifestation of the electromagnetic activity of a magnetized, rotating neutron star in a binary system. Accreting matter from the companion is initially accumulated at the magnetosphere. When the accumulated mass is such that the inflow can start, together with the accretion flare there will be a burst due to the closure of electric currents. The luminosity associated to the latter effect may be as large as 1042 erg/s, if a neutron star possesses the following characteristics: massM =M , period of rotationP = 5 ms, magnetic fieldB 0 = 1012 G, and radiusr 0 = 106 cm. The electromagnetic activity might be relevant for understanding soft gamma ray repeaters.  相似文献   

19.
In this paper, an approximate method of calculating the Fermi energy of electrons (E F (e)) in a high-intensity magnetic field, based on the analysis of the distribution of a neutron star magnetic field, has been proposed. In the interior of a neutron star, different forms of intense magnetic field could exist simultaneously and a high electron Fermi energy could be generated by the release of magnetic field energy. The calculation results show that: E F (e) is related to density ρ, the mean electron number per baryon Y e and magnetic field strength B.  相似文献   

20.
We consider the cooling of neutron stars with superfluid cores composed of neutrons, protons, and electrons (for singlet proton pairing and triplet neutron pairing). The emphasis is on triplet neutron pairing with the component of the total moment of neutron pairs along the quantization axis |m J | = 2. This case stands out in that it leads to power-law rather than exponential suppression of the main neutrino processes by neutron superfluidity. For the chosen critical neutron temperatures T cn, the cooling with |m J | = 2 proceeds either almost in the same way as the commonly considered cooling with m J =0 or appreciably faster. The cooling with variable (over the core) critical temperatures T cn(ρ) and T cp(ρ) can generally be described by the cooling with some effective constant temperatures T cn and T cp. The hypothesis of strong neutron superfluidity with |m J | = 2 is in conflict with the observational data on the thermal radiation from isolated neutron stars; the hypothesis of weak neutron superfluidity of any type is consistent with the observations.  相似文献   

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