The dynamics of a self-gravitating neutron gas in presence of a magnetic field is being studied taking the equation of state of a magnetized neutron gas obtained in a previous study [2]. We work in a Bianchi I spacetime characterized by a Kasner metric, this metric allow us to take into account the anisotropy that introduces the magnetic field. The set of Einstein-Maxwell field equations for this gas becomes a dynamical system in a 4-dimensional phase space. We get numerical solutions of the system. In particular there is a unique point like solution for different initial conditions. Physically this singular solution may be associated with the collapse of a local volume of neutron material within a neutron star.
The steady-state structure of self-gravitating, magnetized accretion disks is studied using a set of self-similar solutions which are appropriate in the outer regions. The disk is assumed to be isothermal and the magnetic field outside of the disk is treated in a phenomenological way. However, the internal field is determined self-consistently. The behaviour of the solutions are investigated by changing the input parameters of the model, i.e. mass accretion rate, coefficients of viscosity and resistivity, and the magnetic field configuration.
We present the first global simulations of self-gravitating magnetized tori. The simulations are performed with Zeus-2D and GLOBAL. We find the magnetorotational instability (MRI) to behave similarly in a self-gravitating environment as in previous simulations of non self-gravitating systems: enhancement of turbulent angular momentum transport follows the linear phase. The torus quickly develops a two component structure composed of an inner thick disk in Keplerian rotation and an outer massive disk. We compare this result with zero mass global simulations in 2D, and also present preliminary r…
Ordinary differential equations describing the self-similar collapse of a rotating, magnetized, self-gravitating and isothermal filament are derived. Explicit homologous solutions are studied with special emphasis on the bifurcation that occurs at the magnetosonic critical point. It is shown that there is a critical value for the toroidal magnetic field slope at the origin above which no bifurcation occurs, the solution remains homologous, and below which the density and the poloidal magnetic field tend to zero at large radius (envelope) whereas the toroidal magnetic field and azimuthal veloci…
In this paper and a companion work, we report on the first global numerical simulations of self-gravitating magnetized tori, subject in particular to the influence of the magnetorotational instability (MRI). In this work, paper I, we restrict our calculations to the study of the axisymmetric evolution of such tori. Our goals are twofold: (1) to investigate how self-gravity influences the global structure and evolution of the disks; and (2) to determine whether turbulent density inhomogeneities can be enhanced by self-gravity in this regime. As in non self-gravitating models, the linear growth …
The self-similar equilibrium models of self-gravitating, rotating, isothermal systems are investigated analytically. In these models the rotation velocity is constant and the density varies as $\frac{f(θ, ϕ)}{r^2}$, where $r$ and $θ$ are the spherical radius and the co-latitude, respectively. The nonaxisymmetric solutions contain three free parameters, one of the parameters depends on the rotation velocity. These parameters determine the overall shape of the density distribution. By assuming that the dominant component of the magnetic field is purely toroidal and the ratio of the purely toroid…
We present the results of a numerical magnetohydrodynamic simulation that demonstrates a mechanism by which magnetic fields tap rotational energy of a stellar core and expel the envelope. Our numerical setup, designed to focus on the basic physics of the outflow mechanism, consists of a solid, gravitating sphere, which may represent the compact core of a star, surrounded by an initially hydrostatic envelope of ionized gas. The core is threaded by a dipolar magnetic field that also permeates the envelope. At the start of the simulation, the core begins to rotate at 10% of the escape speed. The …
We use ZEUS-MP to perform high resolution, three-dimensional, super-Alfvenic turbulent simulations in order to investigate the role of magnetic fields in self-gravitating core formation within turbulent molecular clouds. Statistical properties of our super-Alfvenic model without gravity agree with previous similar studies. Including self-gravity, our models give the following results. They are consistent with the turbulent fragmentation prediction of the core mass distribution of Padoan & Nordlund. They also confirm that local gravitational collapse is not prevented by magnetohydrodynamic wave…
The molecular component of the Galaxy is comprised of turbulent, magnetized clouds, many of which are self-gravitating and form stars. To understand how these clouds' evolution may depend on their level of turbulence, mean magnetization, and degree of self-gravity, we perform a survey of direct numerical MHD simulations in 2.5 dimensions. Two of our independent survey parameters allow us to model clouds which either meet or fail conditions for magneto-Jeans stability and magnetic criticality. Our third survey parameter allows us to initiate turbulence of either sub- or super-Alfvénic amplitude…
A linear stability analysis has been performed onto a self-gravitating magnetized gas disk bounded by external pressure. The resulting dispersion relation is fully explained by three kinds of instability: a Parker-type instability driven by self-gravity, usual Jeans gravitational instability and convection. In the direction parallel to the magnetic fields, the magnetic tension completely suppresses the convection. If the adiabatic index $γ$ is less than a certain critical value, the perturbations trigger the Parker as well as the Jeans instability in the disk. Consequently, the growth rate cur…
We present 3D magnetohydrodynamic (MHD) numerical simulations of the evolution of self--gravitating and weakly magnetized disks with an adiabatic equation of state. Such disks are subject to the development of both the magnetorotational and gravitational instabilities, which transport angular momentum outward. As in previous studies, our hydrodynamical simulations show the growth of strong m=2 spiral structure. This spiral disturbance drives matter toward the central object and disappears when the Toomre parameter Q has increased well above unity. When a weak magnetic field is present as well,…
We consider a magnetized degenerate gas of fermions as the matter source of a homogeneous but anisotropic Bianchi I spacetime with a Kasner--like metric. We examine the dynamics of this system by means of a qualitative and numerical study of Einstein-Maxwell field equations which reduce to a non--linear autonomous system. For all initial conditions and combinations of free parameters the gas evolves from an initial anisotropic singularity into an asymptotic state that is completely determined by a stable attractor. Depending on the initial conditions the anisotropic singularity is of the ``cig…
To be a formation mechanism of such large-scale structures as giant molecular clouds (GMCs) and HI superclouds, the classical Parker instability driven by external gravity has to overcome three major obstacles: The convective motion accompanying the instability generates thin sheets than large condensations. The degree of density enhancement achieved by the instability is too low to make dense interstellar clouds. The time and the length scales of the instability are significantly longer and larger than the estimated formation time and the observed mean separation of the GMCs, respectively. Th…
We investigate the susceptibility of gaseous, magnetized galactic disks to formation of self-gravitating condensations using two-dimensional, local models. We focus on two issues: (1) determining the threshold condition for gravitational runaway, taking into account nonlinear effects, and (2) distinguishing the magneto-Jeans instability (MJI) that arises under inner-galaxy rotation curves from the modified swing amplification (MSA) that arises under outer-galaxy rotation curves. For axisymmetric density fluctuations, instability is known to require a Toomre parameter Q<1. For nonaxisymmetric f…
We examine the effect of self-gravity in a rotating thick-disk equilibrium in the presence of a dipolar magnetic field. In the first part, we find a self-similar solution for non-self-gravitating disks. The solution that we have found shows that the pressure and density equilibrium profiles are strongly modified by a self-consistent toroidal magnetic field. We introduce 3 dimensionless variables $C_B$, $C_c$, $C_t$ that indicate the relative importance of toroidal component of magnetic field ($C_B$), centrifugal ($C_c$) and thermal ($C_t$) energy with respect to the gravitational potential ene…
We use the Bianchi-I spacetime to study the local dynamics of a magnetized self-gravitating Fermi gas. The set of Einstein-Maxwell field equations for this gas becomes a dynamical system in a 4-dimensional phase space. We consider a qualitative study and examine numeric solutions for the degenerate zero temperature case. All dynamic quantities exhibit similar qualitative behavior in the 3-dimensional sections of the phase space, with all trajectories reaching a stable attractor whenever the initial expansion scalar H_{0} is negative. If H_{0} is positive, and depending on initial conditions, t…
The conventional picture of disk accretion onto magnetized neutron stars has been challenged by the spin changes observed in a few X-ray pulsars, and by theoretical results from numerical simulations of disk-magnetized star interactions. These indicate possible accretion during the propeller regime and the spin-down torque increasing with the accretion rate. Here we present a model for the accretion torque exerted by the disk on a magnetized neutron star, assuming accretion continues even for rapid rotators. The accretion torque is shown to have some different characteristics from that in the …
In the atmospheric plasma of a strongly magnetized neutron star, vacuum polarization can induce a Mikheyev-Smirnov-Wolfenstein like resonance across which a X-ray photon may (depending on its energy) convert from one mode into the other, with significant changes in opacities and polarizations. We show that this vacuum resonance effect gives rise to an unique energy-dependent polarization signature in the surface emission from neutron stars. The detection of polarized X-rays from neutron stars can provide a direct probe of strong-field quantum electrodynamics and constrain the neutron star magn…
Recently launched x-ray telescopes have discovered several candidate isolated neutron stars. The thermal radiation from these objects may potentially constrain our understanding of nuclear physics in a realm inaccessible to terrestrial experiments. To translate the observed fluxes from neutron stars into constraints, one needs precise calculations of the heat transfer through the thin insulating envelopes of neutron stars. We describe models of the thermal structure of the envelopes of neutron stars with magnetic fields up to 10^{14} G. Unlike earlier work, we infer the properties of envelope …
The neutrino emissivities resulting from direct URCA processes in neutron stars are calculated in a relativistic Dirac-Hartree approach in presence of a magnetic field. In a quark or a hyperon matter environment, the emissivity due to nucleon direct URCA processes is suppressed relative to that from pure nuclear matter. In all the cases studied, the magnetic field enhances emissivity compared to the field-free cases.
It is suggested that the accretion disk excites the eigen modes of Alfven oscillations of the magnetic field tubes the ends of which are frozen to the neutron star surface. The resonance takes place when the eigen Alfven frequency coincides with the difference of the Keplerian disk rotation frequency and the frequency of rotation of a neutron star. This model explains the two narrow lines of QPO oscillations in kHz band and permits to calculate the masses and radii of the neutron stars in X-ray binaries.
We show that the expected inhomogeneous temperature distribution induced at the surface of a neutron star by the anisotropy of heat transport in the magnetized envelope allows us to understand quite well the observed pulse profiles of the four nearby pulsars for which surface thermal emission has been detected. However, due to gravitational lensing, dipolar magnetic fields are not adequate and the observed high pulsed fractions force us to include a quadrupolar component.
We present two-dimensional simulations for the cooling of neutron stars with strong magnetic fields (B > 1e13 Gauss). We study how the cooling curves are influenced by magnetic field decay. We show that the Joule heating effects are very large and in some cases control the thermal evolution. We characterize the temperature anisotropy induced by the magnetic field and predict the surface temperature distribution for the early and late stages of the evolution of isolated neutron stars, comparing our results with available observational data of isolated neutron stars.
Recent observations of thermally emitting isolated neutron stars revealed spectral features that could be interpreted as radiative transitions of He in a magnetized neutron star atmosphere. We present Hartree-Fock calculations of the polarization-dependent photoionization cross sections of the He atom in strong magnetic fields ranging from 10^12 G to 10^14 G. Convenient fitting formulae for the cross sections are given as well as related oscillator strengths for various bound-bound transitions. The effects of finite nucleus mass on the radiative absorption cross sections are examined using per…
The thermal structure of neutron stars with magnetized envelopes is studied using modern physics input. The relation between the internal (T_i) and local surface temperatures is calculated and fitted by analytic expressions for magnetic field strengths B from 0 to 10^{16} G and arbitrary inclination of the field lines to the surface. The luminosity of a neutron star with dipole magnetic field is calculated and fitted as a function of B, T_i, stellar mass and radius. In addition, we simulate cooling of neutron stars with magnetized envelopes. In particular, we analyse ultramagnetized envelopes …
Surface thermal emission has been detected by ROSAT from four nearby young neutron stars. Assuming black body emission, the significant pulsations of the observed light curves can be interpreted as due to large surface temperature differences produced by the effect of the crustal magnetic field on the flow of heat from the hot interior toward the cooler surface. However, the energy dependence of the modulation observed in Geminga is incompatible with blackbody emission: this effect will give us a strong constraint on models of the neutron star surface.
Thermal surface radiation has been detected with X-ray instruments for several neutron stars with high spectral, spatial and timing resolution. These observations allow for direct study of fundamental properties of the source, but require model atmospheres and spectra for careful interpretation. We describe a robust and extensible implementation of complete linearization for computing the spectra of isolated cooling neutron stars for a broad range of temperature and magnetic field. Self-consistent spectra are derived for arbitrary magnetic field geometries at $B \leq 10^{14}$ G.
We study the thermal structure of neutron stars with magnetized envelopes composed of accreted material, using updated thermal conductivities of plasmas in quantizing magnetic fields, as well as equation of state and radiative opacities for partially ionized hydrogen in strong magnetic fields. The relation between the internal and local surface temperatures is calculated and fitted by an analytic function of the internal temperature, magnetic field strength, angle between the field lines and the normal to the surface, surface gravity, and the mass of the accreted material. The luminosity of a …
It is shown explicitly that if only the zeroth Landau level is occupied by electrons in strongly magnetized neutron star matter in $β$-equilibrium condition, then both the proton and neutron matter sectors become spin symmetric. Whereas, the study of Pauli para-magnetism of neutron matter sector shows that such a scenario is physically impossible. It is also shown that in dense stellar hadronic matter in $β$-equilibrium in presence of strong quantizing magnetic field, with $σ-ω-ρ$ exchange type mean field interaction and with the inclusion of magnetic dipole moments does not allow electrons to…
We study the synchrotron emission of neutrino pairs by relativistic, degenerate electrons in strong magnetic fields. Particular attention is paid to the case in which the dominant contribution comes from one or several lowest cyclotron harmonics. Calculations are performed using the exact quantum formalism and the quasiclassical approach. Simple analytic fits to the neutrino synchrotron emissivity are obtained in the domain of magnetized, degenerate and relativistic electron gas provided the electrons populate either many Landau levels or the ground level alone. The significance of the neutrin…
The cohesive energy of condensed matter in strong magnetic fields is a fundamental quantity characterizing magnetized neutron star surfaces. The cohesive energy refers to the energy required to pull an atom out of the bulk condensed matter at zero pressure. Theoretical models of pulsar and magnetar magnetospheres depend on the cohesive properties of the surface matter in strong magnetic fields. For example, depending on the cohesive energy of the surface matter, an acceleration zone ("polar gap") above the polar cap of a pulsar may or may not form. Also, condensation of the neutron star surfac…
The atmospheres of weakly-magnetized neutron stars expand hydrostatically and rotate differentially during thermonuclear X-ray bursts. Differential rotation is probably related to the frequency drifts of millisecond burst oscillations exhibited by about a dozen nuclear-powered X-ray pulsars. Here, we analyze the linear stability of this differential rotation with respect to local, axisymmetric, multi-diffusive MHD perturbations, at various heights in the neutron star atmosphere. Unstable magneto-rotational modes are identified from within to well above the burning layers. Properties of the fas…
We study the effect of magnetic field on the bulk viscosity of nuclear matter in neutron stars. We employ the framework of relativistic mean field theory to observe the dense nuclear matter in neutron stars. The effects are first studied for the case when the magnetic field does not exceed the critical value to confine the electrons to the lowest Landau levels. We then consider the case of intense magnetic field to evaluate viscosity for the URCA processes and show that the inequality $p_{F}(e)+p_{F}(p)\geq p_{F}(n)$ is no longer required to be satisfied for the URCA processes to proceed.
Non-stationary column accretion onto a surface of a magnetized neutron star is studied with a numerical code based on modified first-order Godunov method with splitting. Formation and evolution of shocks in the column is modeled for accretion rates ranging from 10^{15} g/s to 10^{16} g/s and surface magnetic fields ranging from 5*10^{11} G to 10^{13} G. Non-stationary solutions with plasma deceleration at collisionless oscillating shocks are found. The kinetic energy of the accreting flow efficiently transforms into a cyclotron radiation field. Collisionless stopping of the flow allows a subst…
The SN explosion in the closed binary can give the magnetospheric flare possessing the properties of GRB. The SN shock, flowing around the magnetosphere of a magnetized neutron star or a white dwarf, produces a narrow magnetic tail 10^9 cm long, 10^8 cm wide and a magnetic field of 10^6 Gauss. Fast particles (Lorentz factor of 10^4), generated in the tail by reconnection processes, radaite gamma rays of the 100 KeV - 1 MeV energies. The duration of radiation T<1 sec corresponds to a short GRB. Apart, the powerful shock can tear and accelerate part of the tail. That is the relativistic, strongl…
(Abridged) We develop an analytical spectral method to solve the equations of equilibrium for a self-gravitating, magnetized fluid body, under the only hypotheses that (a) the equation of state is isothermal, (b) the configuration is scale-free, and (c) the body is electrically neutral. All physical variables are represented as series of scalar and vector spherical harmonics of degree l and order m, and the equilibrium equations are reduced to a set of coupled quadratic algebraic equations for the expansion coefficients of the density and the magnetic vector potential. The method is general, a…
In this letter we calculate the energy loss of highly magnetized neutron star due to friction with quantum vacuum, namely Quantum Vacuum Friction (QVF). Taking into account one-loop corrections in the effective Heisenberg-Euler Lagrangian of the light-light interaction, we derive an analytic expression for QVF allowing us to consider magnetic field at the surface of the star as high as $10^{11} $T. In the case of magnetars with high magnetic field above the QED critical field, we show that the energy loss by QVF dominates the energy loss process. This has important consequences, in particular …
The effect of strong quantizing magnetic field on the nucleation of quark matter droplets and on the chemical evolution of nascent quark phase at the core of a neutron star are investigated. The surface energy of quark phase diverges logarithmically. As a consequence there can not be a first order transition to quark phase. However, a metal-insulator type of second order transition is possible unless the field strength exceeds $10^{20}$G. The study of chemical evolution of newborn quark phase shows that in $β$-equilibrium the system becomes energetically unstable.
We calculate axisymmetric toroidal modes of magnetized neutron stars with a solid crust. We assume the interior of the star is threaded by a poloidal magnetic field that is continuous at the surface with the outside dipole field whose strength $B_p$ at the magnetic pole is $B_p\sim 10^{16}$G. Since separation of variables is not possible for oscillations of magnetized stars, we employ finite series expansions of the perturbations using spherical harmonic functions to represent the angular dependence of the oscillation modes. For $B_p\sim 10^{16}$G, we find distinct mode sequences, in each of w…
In this paper, we initiate a new study of steady funnel-flow accretion onto strongly magnetized neutron stars, including a full treatment of shock generation. As a first step, we adopt a simplified model considering the flow within Newtonian theory and neglecting radiative pressure and cooling. The flow is taken to start from an accretion disc and then to follow magnetic field lines, forming a transonic funnel flow onto the magnetic poles. A standing shock occurs at a certain point in the flow and beyond this material accretes subsonically onto the star with high pressure and density. We calcu…
Very early optical and near infrared (IR) emission was discovered accompanying the long gamma-ray burst (GRB) 041219a. We show that the optical/IR flash tracking the gamma-ray lightcurve during the prompt emission could be understood as emission from neutron-rich internal shocks, as has been suggested by Fan & Wei. The early K_s-band afterglow lightcurve after the prompt phase could be well-modeled as the superposition of a reverse shock and a forward shock component. The radio data also support the reverse shock interpretation.
We present global 2D and 3D simulations of self-gravitating magnetized tori. We used the 2D calculations to demonstrate that the properties of the MRI are not affected by the presence of self-gravity: MHD turbulence and enhanced angular momentum transport follow the linear growth of the instability. In 3D, we have studied the interaction between an $m=2$ gravitational instability and MHD turbulence. We found its strength to be significantly decreased by the presence of the latter, showing that both instabilities strongly interact in their non-linear phases. We discuss the consequences of these…
We construct partially ionized hydrogen atmosphere models for magnetized neutron stars in radiative equilibrium with surface fields B=10^12-5 \times 10^14 G and effective temperatures T_eff \sim a few \times 10^5-10^6 K. These models are based on the latest equation of state and opacity results for magnetized, partially ionized hydrogen plasmas that take into account various magnetic and dense medium effects. The atmospheres directly determine the characteristics of thermal emission from isolated neutron stars. For the models with B=10^12-10^13 G, the spectral features due to neutral atoms lie…
We present a detailed investigation of atmospheres around accreting neutron stars with high magnetic field ($B\gtrsim 10^{12}$ G) and low luminosity ($L\lesssim 10^{33}$ erg/s). We compute the atmospheric structure, intensity and emergent spectrum for a plane-parallel, pure hydrogen medium by solving the transfer equations for the normal modes coupled to the hydrostatic and energy balance equations. The hard tail found in previous investigations for accreting, non-magnetic neutron stars with comparable luminosity is suppressed and the X-ray spectrum, although still harder than a blackbody at t…
We carried out two dimensional high-resolution magnetohydrodynamic (MHD) simulations of an accretion disk around a weakly magnetized neutron star. General relativistic effects are taken into account by using pseudo-Newtonian potential of Paczýnski, B., P. J. Witta (1980). When magnetic loops connect the neutron star and the accretion disk, the twist injection from the disk or from the rotating neutron star triggers expansion of the loops. Since the expanding magnetic loops prevent inflow toward the magnetic poles of the neutron star, disk matter accumulates on the boundary between the magnetos…
A great deal of interest has been recently raised in connection with the possibility that soft $γ$-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) contain {\em magnetars}, young neutron stars endowed with magnetic fields $\gtrsim 10^{14}$ G. In this paper we calculate thermal spectra from ultra-magnetized neutron stars for values of the luminosity and magnetic field believed to be relevant to SGRs and AXPs. Emergent spectra are found to be very close to a blackbody at the star effective temperature and exhibit a distinctive absorption feature at the proton cyclotron energy $E_{c,p}\sim…
We construct hydrogen atmosphere models for magnetized neutron stars in radiative equilibrium with surface fields B=10^12-5x10^14 G and effective temperatures T_eff a few x 10^5-10^6 K by solving the full radiative transfer equations for both polarization modes in the magnetized hydrogen plasma. The atmospheres directly determine the characteristics of thermal emission from isolated neutron stars. We study the effects of vacuum polarization and bound atoms on the atmosphere structure and spectra. For the lower magnetic field models (B 10^12 G), the spectral features due to neutral atoms lie at…
We investigate the equilibrium properties of self-gravitating magnetized clouds with polytropic equations of state with negative index n. In particular, we consider scale-free isopedic configurations that have constant dimensionless spherical mass-to-flux ratio lambda_r and that may constitute ``pivotal'' states for subsequent dynamical collapse to form groups or clusters of stars. For given Gamma = 1 + 1/n, equilibria with smaller values of lambda_r are more flattened, ranging from spherical configurations with lambda_r = infinity to completely flattened states for lambda_r=1. For a given amo…
We consider the current flow in an accreting rotating neutron star (X-ray pulsator) and propose that the active magnetosphere is limited by the Alfvèn surface. Formulae for the luminosity and torque due to currents circulating in the neutron star are given, and astrophysical consequences for systems like Her X-1 and LMXRB are shortly discussed.
Cooling of neutron stars with dipole magnetic fields is simulated using a realistic model of the anisotropic surface temperature distribution produced by magnetic fields. Suppression of the electron thermal conductivity of outer stellar layers across the field increases thermal isolation of these layers near the magnetic equator. Enhancement of the radiative and longitudinal electron thermal conductivities in quantizing magnetic fields reduces thermal isolation near the magnetic poles. The equatorial increase of the isolation is pronounced for $B \ga 10^{10}$ G, while the polar decrease -- for…
We investigate spherical accretion to a rotating magnetized star in the "propeller" regime using axisymmetric resistive magnetohydrodynamic simulations. The regime is predicted to occur if the magnetospheric radius is larger than the corotation radius and smaller than the light cylinder radius. The simulations show that accreting matter is expelled from the equatorial region of the magnetosphere and that it moves away from the star in a supersonic, disk-shaped outflow. At larger radial distances the outflow slows down and becomes subsonic. The equatorial matter outflow is initially driven by t…
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 $4.4 \times 10^{13}$ 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 article 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 u…
The thermal emission from isolated neutron stars is not well understood. The X-ray spectrum is very close to a blackbody but there is a systematic optical excess flux with respect to the extrapolation to low energy of the best blackbody fit. This fact, in combination with the observed pulsations in the X-ray flux, can be explained by anisotropies in the surface temperature distribution.We study the thermal emission from neutron stars with strong magnetic fields in order to explain the origin of the anisotropy. We find (numerically) stationary solutions in axial symmetry of the heat transporteq…
We report on a new mechanism for heat conduction in the neutron star crust. We find that collective modes of superfluid neutron matter, called superfluid phonons (sPhs), can influence heat conduction in magnetized neutron stars. They can dominate the heat conduction transverse to magnetic field when the magnetic field $B \gsim 10^{13}$ G. At density $ρ\simeq 10^{12}-10^{14} $ g/cm$^3$ the conductivity due to sPhs is significantly larger than that due to lattice phonons and is comparable to electron conductivity when temperature $\simeq 10^8$ K. This new mode of heat conduction can limit the su…
The chemical evolution of nascent quark matter core in a newborn compact neutron star is studied in presence of a strong magnetic field. The effective rate of strange quark production in degenerate quark matter core in presence of strong magnetic fields is obtained. The investigations show that in presence of strong magnetic fields a quark matter core becomes energetically unstable and hence a deconfinement transition to quark matter at the centre of a compact neutron star under such circumstances is not possible. The critical strength of magnetic field at the central core to make the system e…
We examine the dynamics of a self--gravitating magnetized neutron gas as a source of a Bianchi I spacetime described by the Kasner metric. The set of Einstein-Maxwell field equations can be expressed as a dynamical system in a 4-dimensional phase space. Numerical solutions of this system reveal the emergence of a point--like singularity as the final evolution state for a large class of physically motivated initial conditions. Besides the theoretical interest of studying this source in a fully general relativistic context, the resulting idealized model could be helpful in understanding the coll…
We study the equation of state, polarization and radiation properties for nonideal, strongly magnetized plasmas which compose outer envelopes of magnetic neutron stars. Detailed calculations are performed for partially ionized hydrogen atmospheres and for condensed hydrogen or iron surfaces of these stars. This is a companion paper to astro-ph/0511803
Neutron stars with very strong surface magnetic fields have been suggested as the site for the origin of observed soft gamma repeaters (SGRs). In this paper we investigate the influence of such strong magnetic fields on the properties and internal structure of these magnetized neutron stars (magnetars). We study properties of a degenerate equilibrium ideal neutron-proton-electron (npe) gas with and without the effects of the anomalous nucleon magnetic moments in a magnetic field. The presence of a sufficiently strong magnetic field changes the ratio of protons to neutrons as well as the neutro…
In this letter we study the propagation of light in the neighbourhood of magnetised neutron stars. Thanks to the optical properties of quantum vacuum in the presence of a magnetic field, light emitted by background astronomical objects is deviated giving rise to a phenomenon of the same kind as the gravitational one. We give a quantitative estimation of this effect and we discuss the possibility of its observation. We show that this effect could be detected monitoring the evolution of the recently discovered double neutron star system J0737-3039.
Using the Relativistic Mean Field Theory (RMF) it is shown that different proton fraction which is directly connected with the neutron excess and with the asymmetry of the system affects proto-neutron stars parameters and changes their composition. The obtained form of the equation of state allows to construct the mass-radius relations and shows that the increasing asymmetry creates more compact stars. The inclusion of delta meson together with nonlinear vector meson interaction terms and magnetic field make this effect even stronger.
The energy loss rate of a magnetized electron gas emitting axions a due to the process $e^- \to e^- +a$ is derived for arbitrary magnetic field strength B. Requiring that for a strongly magnetized neutron star the axion luminosity is smaller than the neutrino luminosity we obtain the bound $g_{ae}\lsim 10^{-10}$ for the axion electron coupling constant. This limit is considerably weaker than the bound derived earlier by Borisov and Grishina using the same method. Applying a similar argument to magnetic white dwarf stars results in the more stringent bound $g_{ae}\lsim 9x10^{-13} (T/10^7 K)^{5/…
