Neutron Stars 1: Equation of State and Structure

We report the final redshift release of the 6dF Galaxy Survey (6dFGS), a combined redshift and peculiar velocity survey over the southern sky (|b| > 10°). Its 136 304 spectra have yielded 110 256 new extragalactic redshifts and a new catalogue of 125 071 galaxies making near-complete samples with (K, H, J, r_F, b_J) ≤ (12.65, 12.95, 13.75, 15.60, 16.75). The median redshift of the survey is 0.053. Survey data, including images, spectra, photometry and redshifts, are available through an online data base. We describe changes to the information in the data base since earlier interim data releases. Future releases will include velocity dispersions, distances and peculiar velocities for the brightest early-type galaxies, comprising about 10 per cent of the sample. Here we provide redshift maps of the southern local Universe with z ≤ 0.1, showing nearby large-scale structures in hitherto unseen detail. A number of regions known previously to have a paucity of galaxies are confirmed as significantly underdense regions. The URL of the 6dFGS data base is http://www-wfau.roe.ac.uk/6dFGS.

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The 6dF Galaxy Survey: final redshift release (DR3) and southern large-scale structures

Recent Progress and New Challenges in Isospin Physics with Heavy-Ion Reactions

There has recently been growing evidence for the existence of neutron stars possessing magnetic fields with strengths that exceed the quantum critical field strength of 4.4 × 1013 G, at which the cyclotron energy equals the electron rest mass. Such evidence has been provided by new discoveries of radio pulsars having very high spin-down rates and by observations of bursting gamma-ray sources termed magnetars. This paper will discuss the exotic physics of this high-field regime, where a new array of processes becomes possible and even dominant and where familiar processes acquire unusual properties. We review the physical processes that are important in neutron star interiors and magnetospheres, including the behaviour of free particles, atoms, molecules, plasma and condensed matter in strong magnetic fields, photon propagation in magnetized plasmas, free-particle radiative processes, the physics of neutron star interiors and field evolution and decay mechanisms. Application of such processes in astrophysical source models, including rotation-powered pulsars, soft gamma-ray repeaters, anomalous x-ray pulsars and accreting x-ray pulsars will also be discussed. Throughout this review, we will highlight the observational signatures of high magnetic field processes, as well as the theoretical issues that remain to be understood.

Physics of strongly magnetized neutron stars

We report on Bayesian parameter estimation of the mass and equatorial radius of the millisecond pulsar PSR J0030+0451, conditional on pulse-profile modeling of Neutron Star Interior Composition Explorer X-ray spectral-timing event data. We perform relativistic ray-tracing of thermal emission from hot regions of the pulsar’s surface. We assume two distinct hot regions based on two clear pulsed components in the phase-folded pulse-profile data; we explore a number of forms (morphologies and topologies) for each hot region, inferring their parameters in addition to the stellar mass and radius. For the family of models considered, the evidence (prior predictive probability of the data) strongly favors a model that permits both hot regions to be located in the same rotational hemisphere. Models wherein both hot regions are assumed to be simply connected circular single-temperature spots, in particular those where the spots are assumed to be reflection-symmetric with respect to the stellar origin, are strongly disfavored. For the inferred configuration, one hot region subtends an angular extent of only a few degrees (in spherical coordinates with origin at the stellar center) and we are insensitive to other structural details; the second hot region is far more azimuthally extended in the form of a narrow arc, thus requiring a larger number of parameters to describe. The inferred mass M and equatorial radius R eq are, respectively, and , while the compactness is more tightly constrained; the credible interval bounds reported here are approximately the 16% and 84% quantiles in marginal posterior mass.

/pdf/a-nicer-view-of-psr-j0030-0451-millisecond-pulsar-parameter-1uyudonltc.pdf

A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation

The core of a neutron star contains several species of particles, whose relative equilibrium concentrations are determined by the local density. As the star spins down, its centrifugal force decreases continuously, and the star contracts. The density of any given fluid element increases, changing its chemical equilibrium state. The relaxation towards the new equilibrium takes a finite time, so the matter is not quite in chemical equilibrium, and energy is stored that can be released by reactions. For a neutron star core composed of neutrons (n), protons (p), and electrons (e), the departure from chemical equilibrium is quantified by the chemical potential difference $\delta\mu\equiv \mu_{\rm p}+\mu_{\rm e} -\mu_{\rm n}$. A finite $\delta\mu$ increases the reaction rates and the neutrino emissivity. If large enough ($|\delta\mu|\gta 5kT$), it reduces the net cooling rate because some of the stored chemical energy is converted into thermal energy, and can even lead to net heating. A simple model shows the effect of this heating mechanism on the thermal evolution of neutron stars. It is particularly noticeable for old, rapidly spinning stars with weak magnetic fields. Observational consequences for millisecond pulsars are discussed.

Deviations from chemical equilibrium due to spin-down as an internal heat source in neutron stars

Context. Long-lived, large-scale magnetic field configurations exist in upper main sequence, white dwarf, and neutron stars. Externally, these fields have a strong dipolar component, while their internal structure and evolution are uncertain but highly relevant to several problems in stellar and high-energy astrophysics. Aims. We discuss the main properties expected for the stable magnetic configurations in these stars from physical arguments and the ways these properties may determine the modes of decay of these configurations. Methods. We explain and emphasize the likely importance of the non-barotropic, stable stratification of matter in all these stars (due to entropy gradients in main-sequence envelopes and white dwarfs, due to composition gradients in neutron stars). We first illustrate it in a toy model involving a single, azimuthal magnetic flux tube. We then discuss the effect of stable stratification or its absence on more general configurations, such as axisymmetric equilibria involving poloidal and toroidal field components. We argue that the main mode of decay for these configurations are processes that lift the constraints set by stable stratification, such as heat diffusion in main-sequence envelopes and white dwarfs, and beta decays or particle diffusion in neutron stars. We estimate the time scales for these processes, as well as their interplay with the cooling processes in the case of neutron stars. Results. Stable magneto-hydrostatic equilibria appear to exist in stars whenever the matter in their interior is stably stratified (not barotropic). These equilibria are not force-free and not required to satisfy the Grad-Shafranov equation, but they do involve both toroidal and poloidal field components. In main sequence stars with radiative envelopes and in white dwarfs, heat diffusion is not fast enough to make these equilibria evolve over the stellar lifetime. In neutron stars, a strong enough field might decay by overcoming the compositional stratification through beta decays (at the highest field strengths) or through ambipolar diffusion (for somewhat weaker fields). These processes convert magnetic energy to thermal energy, and they occur at significant rates only once the latter is less than the former; therefore, they substantially delay the cooling of the neutron star, while slowly decreasing its magnetic energy.

/pdf/stable-magnetic-equilibria-and-their-evolution-in-the-upper-31mjul6m1g.pdf

Stable magnetic equilibria and their evolution in the upper main sequence, white dwarfs and neutron stars

https://arxiv.org/pdf/astro-ph/9410035.pdf

Deviations from Chemical Equilibrium due to Spin-Down as an Internal Heat Source in Neutron Stars

We present the first application of a spherical collapse model to a supercluster of galaxies. Positions and redshifts of ~3000 galaxies in the Shapley supercluster (SSC) are used to define velocity caustics that limit the gravitationally collapsing structure in its central part. This is found to extend at least to 8 h-1 Mpc of the central cluster, A3558, enclosing 11 ACO clusters. Infall velocities reach ~2000 km s-1. Dynamical models of the collapsing region are used to estimate its mass profile. An upper bound on the mass, based on a pure spherical infall model, gives M(<8 h-1 Mpc) 1.3 ? 1016 h-1 M ? for an Einstein?de Sitter (critical) universe and M(<8 h-1 Mpc) 8.5 ? 1015 h-1 M ? for an empty universe. The Diaferio & Geller model, based on estimating the escape velocity, gives a significantly lower value, M(<8 h-1 Mpc) ? 2.1 ? 1015 h-1 M?, very similar to the mass Geller et al. found around the Coma cluster by the same method and comparable to or slightly lower than the dynamical mass in the virialized regions of clusters enclosed in the same region of the SSC. In both models, the overdensity in this region is substantial, but it is far from the value required to account for the peculiar motion of the Local Group with respect to the cosmic microwave background.

The Shapley Supercluster. III. Collapse Dynamics and Mass of the Central Concentration

We report 2868 new multiobject spectroscopic measurements of galaxy redshifts in an area roughly 12° × 6° (right ascension × declination) centered on the Shapley Supercluster (SSC). These correspond to 2627 different galaxies. Including other measurements reported in the literature, the total number of galaxies with measured redshifts in a 19° × 16° area centered on the supercluster now reaches 5090. Of these, 2949 lie in the redshift range 9000–18,000 km s-1, which we tentatively identify with the SSC. This unprecedented sample allows a quite detailed qualitative morphological study of the SSC. Based on the three-dimensional distribution of galaxies and clusters of galaxies, we identify several subcondensations of the supercluster, as well as walls and filaments connecting them. We also find another supercluster in the background, at redshift ~23,000 km s-1.

Andreas Reisenegger

Papers

Deviations from chemical equilibrium due to spin-down as an internal heat source in neutron stars

Stable magnetic equilibria and their evolution in the upper main sequence, white dwarfs and neutron stars

Deviations from Chemical Equilibrium due to Spin-Down as an Internal Heat Source in Neutron Stars

The Shapley Supercluster. III. Collapse Dynamics and Mass of the Central Concentration

The Shapley Supercluster. II. Spectroscopic Observations in a Wide Area and General Morphology