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Context. In the cooling process of a non-accreting neutron star, the composition and properties of the crust are thought to be fixed at the finite temperature where nuclear reactions fall out of equilibrium. A lower estimate for this temperature is given by the crystallization temperature, which can be as high as 7 ✕ 109 K in the inner crust, potentially leading to sizeable differences with respect to the simplifying cold-catalyzed matter hypothesis. Aims. We extend a recent work on the outer crust to the study of the crystallization of the inner crust and the associated composition in the one-component plasma approximation. Methods. The finite temperature variational equations for non-uniform matter in both the liquid and the solid phases are solved using a compressible liquid-drop approach with parameters optimized on four different microscopic models that cover current uncertainties in nuclear modeling. Results. We consider the effect of the different nuclear ingredients with their associated uncertainties separately: the nuclear equation of state, the surface properties in the presence of a uniform gas of dripped neutrons, and the proton shell effects arising from the ion single-particle structure. Our results suggest that the highest source of model dependence comes from the smooth part of the nuclear functional. Conclusions. We show that shell effects play an important role at the lowest densities close to the outer crust, but the most important physical ingredient to be settled for a quantitative prediction of the inner crust properties is the surface tension at extreme isospin values. [ABSTRACT FROM AUTHOR]

The theory of the nuclear energy-density functional is used to provide a unified and thermodynamically consistent treatment of all regions of cold non-accreting neutron stars. In order to assess the impact of our lack of complete knowledge of the density dependence of the symmetry energy on the constitution and the global structure of neutron stars, we employ four different functionals. All of them were precision fitted to essentially all the nuclear mass data with the Hartree–Fock–Bogoliubov method and two different neutron-matter equations of state based on realistic nuclear forces. For each functional, we calculate the composition, the pressure–density relation, and the chemical potentials throughout the star. We show that uncertainties in the symmetry energy can significantly affect the theoretical results for the composition and global structure of neutron stars. To facilitate astrophysical applications, we construct analytic fits to our numerical results. [ABSTRACT FROM AUTHOR]

We have recently developed a series of accurately calibrated nuclear energy density functionals, fitted to essentially all atomic masses with a model root mean square deviation now reduced to 0.5 MeV for our functional BSk27*. At the same time, these functionals were adjusted to realistic equations of state of neutron matter and were constrained to reproduce various properties of nuclear matter. Using BSk27*, we have calculated the internal constitution and the equation of state of the crust of non-accreting neutron stars. [ABSTRACT FROM AUTHOR]

The TETFSI (temperature-dependent extended Thomas-Fermi plus Strutinsky integral) method for calculating the properties of the inner crust of neutron stars is here extended in the zero-temperature limit to include proton pairing. The main effect is to smooth out the proton shell effects, although the energetically favored value of Z, the number of protons per Wigner-Seitz cell, remains at, or close to, 40. [ABSTRACT FROM AUTHOR]

Aims. In this paper, we study the global properties of neutron stars (NSs), as predicted by the Brussels-Montreal equations of state (EoSs). These EoSs, which provide a unified description of all regions of a NS, are based on the generalised Skyrme functionals BSk19, BSk20, and BSk21 that were simultaneously fitted to almost all the nuclear mass data and constrained to reproduce various properties of infinite nuclear matter, as obtained from microscopic calculations. Methods. We solved Einstein's equations of general relativity for both non-rotating and rigidly rotating NSs using these unified EoSs. Results. The NS properties thus obtained are compared with various astrophysical observations. We find that only the stiffest EoS, based on the functional BSk21, is compatible with all the constraints inferred from these observations. [ABSTRACT FROM AUTHOR]

The equation of state and composition of the inner crust of neutron stars at zero temperature are calculated, using the T = 0 version of the temperature-dependent extended Thomas-Fermi plus Strutinsky integral method, for each of a family of three functionals based on Skyrme-type forces BSkl9, BSk20, and BSk21, which are characterized by different degrees of symmetry-energy stiffness, and also for the SLy4 functional. We also solve the Tolman-Oppenheimer-Völkoff equations to calculate the distribution of mass within the inner crust. Qualitatively similar results are found for all four functionals, and in particular the number of protons per Wigner-Seitz cell is in all cases equal to 40 throughout the inner crust. [ABSTRACT FROM AUTHOR]

We have calculated the zero-temperature properties of the outer crust of neutron stars for four nuclear-mass models based on the Hartree-Fock-Bogoliubov method: the three most recent Skyrme-force models (HFB-19, HFB-20, and HFB-21) and the Gogny-force model D1M. While the equation of state is substantially the same for the four models, the nuclidic composition varies considerably from one model to another. We solve the Tolman-Oppenheimer-Volkoff equations by integrating inward from the surface and thereby determine the abundance of each nuclide in the outer crust of a typical neutron star of mass 1.5M☉ and radius 13 km. Although the total mass of the outer crust is slightly model dependent, its thickness is essentially the same for all four models. [ABSTRACT FROM AUTHOR]

We generalize our earlier work on neutron stars, which assumed spherical Wigner-Seitz cells in the inner crust, to admit the possibility of pasta phases, i.e., nonspherical cell shapes. Full fourth-order extended Thomas-Fermi (ETF) calculations using the density functional BSk24 are performed for cylindrical and platelike cells. Unlike in our spherical-cell calculations we do not include shell and pairing corrections, but there are grounds for expecting these corrections for pasta to be significantly smaller. It is therefore meaningful to compare the ETF pasta results with the full spherical-cell results, i.e., with shell and pairing corrections included. However, in view of the many previous studies in which shell and pairing corrections were omitted entirely, it is of interest to compare our pasta results with the ETF part of the corresponding spherical calculations. Making this latter comparison, we find that as the density increases the cell shapes pass through the usual sequence sphere → cylinder → plate before the transition to the homogeneous core. The filling fractions found at the phase transitions are in close agreement with expectations based on the liquid-drop model. On the other hand, when we compare with the full spherical-cell results, we find the sequence to be sphere → cylinder → sphere → cylinder → plate. In neither case do any "inverted," i.e., bubblelike, configurations appear. The analytic fitting formulas for the equation of state and composition that we derived in our earlier work, with the assumption of spherical cell shapes for the entire density range from the outer crust to the core of a neutron star, are found to remain essentially unchanged for pasta shapes. Here, however, we provide more accurate fitting formulas to all our essential numerical results for each of the three phases, designed especially for the density range where the nonspherical shapes are expected, which enable one to capture not only the general behavior of the fitted functions but also the differences between them in different phases. [ABSTRACT FROM AUTHOR]

We calculate the maximum mass of neutron stars for three different equations of state (EOSs) based on generalized Skyrme functionals that are simultaneously fitted to essentially all the 2003 nuclear mass data (the rms deviation is 0.58 MeV in all three cases) and to one or other of three different equations of state of pure neutron matter, each determined by a different many-body calculation using realistic two- and three-body interactions but leading to significantly different degrees of stiffness at the high densities prevailing in neutron-star interiors. The observation of a neutron star with mass 1.97 ± 0.04 M⊙ eliminates the softest of our models (BSkl9), but does not discriminate between BSk20 and BSk21. However, nuclear-mass measurements that have been made since our models were constructed strongly favor BSk21, our stiffest functional. [ABSTRACT FROM AUTHOR]

The equilibrium properties of the outer crust of cold nonaccreting magnetars (i.e., neutron stars endowed with very strong magnetic fields) are studied using the latest experimental atomic mass data complemented with a microscopic atomic mass model based on the Hartree-Fock-Bogoliubov method. The Landau quantization of electron motion caused by the strong magnetic field is found to have a significant impact on the composition and the equation of state of crustal matter. It is also shown that the outer crust of magnetars could be much more massive than that of ordinary neutron stars. [ABSTRACT FROM AUTHOR]