Nucleus-acoustic solitary waves in white dwarfs

The formation of nucleus-acoustic solitary waves (NASWs), and their basic properties in white dwarfs containing non-relativistically or ultra-relativistically degenerate electrons, non-relativistically degenerate light nuclei, and stationary heavy nuclei have been theoretically investigated. The reductive perturbation method, which is valid for small but finite amplitude NASWs, is used. The NASWs are, in fact, associated with the nucleus acoustic (NA) waves in which the inertia is provided by the light nuclei, and restoring force is provided by the degenerate pressure of electrons. On the other hand, stationary heavy nuclei maintain the background charge neutrality condition. It has been found that the presence of the heavy nuclei significantly modify the basic features (polarity, amplitude, width, and speed) of the NASWs. The basic properties are also found to be significantly modified by the effects of ultra-relativistically degenerate electrons and relative number densities of light and heavy nuclei. The implications of our results in white dwarfs are pinpointed.     

The astrophysics of cool white dwarfs

Old, cool white dwarfs convey valuable information about the early history of our Galaxy. They have been used to determine the age of the Galactic disk, several open clusters and a globular cluster. We review the current understanding of the physics of cool white dwarfs, including their mass distribution, chemical evolution, and cooling. We also examine the role of white dwarfs as tracers of various stellar populations, both in terms of observational searches and theoretical models.     

Molecular magnetic dichroism in spectra of white dwarfs

We present novel calculations of the magnetic dichroism appearing in molecular bands in the presence of a strong magnetic field, which perturbs the internal structure of the molecule and results in net polarization due to the Paschen-Back effect. Based on that, we analyze new spectropolarimetric observations of the cool magnetic helium-rich white dwarf G99-37, which shows strongly polarized molecular bands in its spectrum. In addition to previously known molecular bands of the C2 Swan and CH A-X systems, we find a firm evidence for the violet CH B-X bands at 390 nm and C2 Deslandres-d'Azambuja bands at 360 nm. Combining the polarimetric observations with our model calculations, we deduce a dipole magnetic field of 7.5+/-0.5 MG with the positive pole pointing towards the Earth. We conclude that the developed technique is an excellent tool for studying magnetic fields on cool magnetic stars.     

Heavy-and light-nuclei acoustic dressed shock waves in white dwarfs

In this investigation, the evolution of heavy-and light-nuclei acoustic (HLNA) dressed shock waves (DSWs) due to the contribution of higher order of nonlinearity and dissipation effects has been examined in a degenerate quantum plasma composed of inertial heavy as well as light nuclei and inertia-less ultra-relativistic degenerate electrons. By employing the reductive perturbation method, the nonlinear Burgers equation is derived. Further, an inhomogeneous Burgers-type equation accounting for the higher order contributions of nonlinearity and dissipation is also derived. With the insertion of higher order effects, a new humped type or dressed shock structures are evolved. The influence of different plasma parameters on the dynamical evolution of the HLNA-DSWs is examined. It is observed that these plasma parameters play significant role on the characteristics of HLNA-DSWs and their corresponding electric fields. The findings of present investigation may be applicable to provide a new insight to understand the evolution of HLNA-DSWs in different dense astrophysical regions such as white dwarfs.     

Bremsstrahlung model of polarized radiation from magnetic white dwarfs

Motivated by the desire to provide a model for the polarized radiation observed from some white dwarfs, we calculate the intensities of right and left circularly polarized bremsstrahlung radiation emitted by electrons in the atmospheres of magnetic white dwarfs.     

Probing white dwarf interiors with LISA: periastron precession in eccentric double white dwarfs

In globular clusters, dynamical interactions give rise to a population of eccentric double white dwarfs detectable by the Laser Interferometer Space Antenna (LISA) up to the Large Magellanic Cloud. In this Letter, we explore the detectability of periastron precession in these systems with LISA. Unlike previous investigations, we consider contributions due to tidal and rotational distortions of the binary components in addition to general relativistic contributions to the periastron precession. At orbital frequencies above a few mHz, we find that tides and stellar rotation dominate, opening up a possibly unique window to the study of the interior and structure of white dwarfs.     

Generalized uncertainty principle and the maximum mass of ideal white dwarfs

The effects of a generalized uncertainty principle on the structure of an ideal white dwarf star is investigated. The equation describing the equilibrium configuration of the star is a generalized form of the Lane–Emden equation. It is proved that the star always has a finite size. It is then argued that the maximum mass of such an ideal white dwarf tends to infinity, as opposed to the conventional case where it has a finite value.     

General relativistic aspects of ferromagneto-fluid

The implications of Bianchi identities pertaining to the spacetime of relativistic ferrofluid with infinite conductivity and variable magnetic permeability are investigated. Some kinematical and dynamical corollaries emerging out of a preferred geometrical symmetry called an isometry with respect to the flow vector and the magnetic field vector are developed.     

General relativistic stability of Q matter

The theory governing the general relativistic structure of matter composed of a doublet of SO(2) scalar fields is examined. Coleman's observation that an internal rotation in SO(2) space can stabilize a Q ball prior to the breaking of global symmetry SO(2) is suggestive of the possibility that such stable objects may be seeded in the early universe.     

General relativistic collapse of rotating stars

Numerical calculations have been made for the formation process of rotating black holes. It is suggested that Kerr black holes may be formed for wide ranges of initial conditions if q (=| total angular momentum |M²) is smaller than unity. For q > 1, an expanding disk or a jet appears.     

Point massive particle in General Relativity

It is well known that the Schwarzschild solution describes the gravitational field outside compact spherically symmetric mass distribution in General Relativity. In particular, it describes the gravitational field outside a point particle. Nevertheless, what is the exact solution of Einstein’s equations with $\delta $ δ -type source corresponding to a point particle is not known. In the present paper, we prove that the Schwarzschild solution in isotropic coordinates is the asymptotically flat static spherically symmetric solution of Einstein’s equations with $\delta $ δ -type energy-momentum tensor corresponding to a point particle. Solution of Einstein’s equations is understood in the generalized sense after integration with a test function. Metric components are locally integrable functions for which nonlinear Einstein’s equations are mathematically defined. The Schwarzschild solution in isotropic coordinates is locally isometric to the Schwarzschild solution in Schwarzschild coordinates but differs essentially globally. It is topologically trivial neglecting the world line of a point particle. Gravity attraction at large distances is replaced by repulsion at the particle neighborhood.     

General massive multiplets in extended supersymmetry

We consider the extended Poincaré superalgebra in four dimensions with general central charge operators. We find the invariance of this algebra and the particle supermultiplets with their internal symmetry properties. Central charges obtained by dimensional reduction appear as a special case in this classification.     

The mass limit of white dwarfs with strong magnetic fields in general relativity

Recently, U. Das and B. Mukhopadhyay proposed that the Chandrasekhar limit of a white dwarf could reach a new high level(2.58M) if a superstrong magnetic field were considered(Das U and Mukhopadhyay B 2013 Phys. Rev.Lett. 110 071102), where the structure of the strongly magnetized white dwarf(SMWD) is calculated in the framework of Newtonian theory(NT). As the SMWD has a far smaller size, in contrast with the usual expectation, we found that there is an obvious general relativistic effect(GRE) in the SMWD. For example, for the SMWD with a one Landau level system, the super-Chandrasekhar mass limit in general relativity(GR) is approximately 16.5% lower than that in NT.More interestingly, the maximal mass of the white dwarf will be first increased when the magnetic field strength keeps on increasing and reaches the maximal value M = 2.48 M with BD = 391.5. Then if we further increase the magnetic fields,surprisingly, the maximal mass of the white dwarf will decrease when one takes the GRE into account.     

General relativistic dynamics of compact binary systems

The equations of motion of compact binary systems have been derived in the post-Newtonian (PN) approximation of general relativity. The current level of accuracy is 3.5PN order. The conservative part of the equations of motion (neglecting the radiation reaction damping terms) is deducible from a generalized Lagrangian in harmonic coordinates, or equivalently from an ordinary Hamiltonian in ADM coordinates. As an application, we investigate the problem of the dynamical stability of circular binary orbits against gravitational perturbations up to the 3PN order. We find that there is no innermost stable circular orbit or ISCO at the 3PN order for equal masses. To cite this article: L. Blanchet, C. R. Physique 8 (2007).     

New insights into the limit of the magnetic monopole flux and the heating source in white dwarfs

Based on the magnetic monopole(MM) catalytic nuclear decay(Rubakov-Callan(RC) effect),we propose five new models to discuss the limit of the MM flux and the heating energy resources of white dwarfs(WDs)based on observations of 13 red giant branch(RGB) stars.We find that the number of MMs captured can reach a maximum value of 9.1223 × 10²⁴ when m=1017 GeV,n_B=5.99×10³¹ cm^-3,φ=7.59×10^-26cm^-2s^-1sr^-1.The good agre...     

Quantum effects in relativistic decays

By using both explicit time-dependent andS-matrix formalisms of relativistic quantum theory we calculate the decay law of a moving unstable system and show that the classical Einstein time dilation formula is not rigorously applicable in this case and quantum corrections should be taken into account. The consistency of experimental data with Einstein's time dilation formula and the absence of translation-induced decays indicate that the interactions responsible for decays belong to the Dirac instant form dynamics rather than to the point form dynamics. Our results suggest that even though the different forms of dynamics are scattering-equivalent, they are not exactly physically equivalent, as was thought before. Three different experiments with unstable particles are discussed which allow one in principle to determine the details of the interaction governing the decay.On leave from the Institute of Chemical Physics, University of Latvia, Riga, LV-1586, Latvia.     

Non-equilibrium effects in relativistic hydrodynamics

We review Smoothed Particle Hydrodynamics (SPH) for ultrarelativistic nuclear collisions. Possible extensions of the usual formulation are discussed, incorporating the fundamentally important single-event fluctuations originating in turbulent or quantum mechanical motion.     

General relativistic galvano-gravitomagnetic effect in current carrying conductors

The analogy between general relativity and electromagnetism suggests that there is a new galvano-gravitomagnetic effect, which is the gravitational analog of the Hall effect and takes place when a current carrying conductor is placed in a gravitomagnetic field. In connection with this galvano-gravitomagnetic effect, we explore the possibility of using current carrying conductors for detecting the gravitomagnetic field of the Earth.     

Kramers' theorem in the relativistic electronic structure calculation

In a crystal with a centre of inversion with no spin polarization present all bands of the relativistic band structure are twofold degenerate due to Kramers' theorem. This symmetry can be used to reduce the numerical expense of relativistic band structure calculations by a factor of 2. The reduction which is described in this paper does however not follow the standard lines of the group theoretical treatment of the quantum mechanical eigenvalue problem. The complication arises from the anti-unitarity of the symmetry operator.