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A review of the main foundations of cosmology and its current state is presented. [ABSTRACT FROM AUTHOR]

The problem of the passage of light through the mouth of a zero-mass wormhole and the possibility of observing the objects from another asymptotically flat space-time through the mouth of a wormhole are considered. It is shown that an individual star can have several images and the fact that the image of a flat Lambertian screen has a complex brightness distribution for an observer located on the opposite side of the throat. Images of two such screens visible inside the silhouette of a massless wormhole and the distribution of radiation intensity in their images are constructed. [ABSTRACT FROM AUTHOR]

This paper refutes the erroneous statements that arose in theoretical cosmology almost 90 years ago. The method accepted in the literature for deriving the local properties of the Friedmann cosmological model, using only Newton theory, without resorting to Einstein theory, is considered. We showed that the usual method of such inference is not sufficient to obtain the correct result, and leads to errors. Requirements are formulated that are sufficient for the Newtonian model to really be an approximation to the relativistic theory. [ABSTRACT FROM AUTHOR]

The problem of bending and scattering of light rays passing outside the entrance of a wormhole with zero gravitational mass is considered. The process of ray capture by a wormhole, as well as the formation process of a shadow when illuminated by a standard screen, is investigated. These mechanisms are also compared to the case of light ray motion in the vicinity of the Schwarzschild black hole. [ABSTRACT FROM AUTHOR]

The spatial properties of the entrances to spherically symmetric black holes and wormholes with zero and positive masses are compared. The properties were studied in terms of bulk and brane. The explicit expressions for the entrances are found and it is shown that in both representations the spatial funnels of the entrances to the wormholes are the steepest for the Schwarzschild black holes, and the least steep for the wormholes with zero mass. [ABSTRACT FROM AUTHOR]

Based on Khalatnikov's ideas, we consider the physical processes that arise in the collapse of wormholes of different types. We emphasize that the physical processes during the collapse and their outcome depend significantly on the type of wormhole. We consider in detail how black holes arise in the collapse of wormholes. [ABSTRACT FROM AUTHOR]

A model of a star consisting of vacuum-like matter is constructed in the framework of general relativity. Its stability and other physical properties are analyzed. This stellar model is compared with cosmological models consisting of the same vacuum-likematter with a pressure equal to the energy density but with the opposite sign. [ABSTRACT FROM AUTHOR]

The role of pressure as a source of gravity in general relativity is considered. In homogeneous, anisotropic cosmological models, the anisotropic pressure components along different coordinate axes are included as terms in the equations determining the accelerations along these axes; in this sense, this situation is similar to how the mass density is included in these equations. A change in the pressure component along one of the coordinates leads to an anisotropic change in the accelerations along all three coordinates. However, the pressure components are not present in the equation determining the initial conditions. On the other hand, with an inhomogeneous matter density distribution, the mass density and pressure play fundamentally different roles as sources of gravity. The consequences of this are considered. [ABSTRACT FROM AUTHOR]

In this paper, the electromagnetic bremsstrahlung spectrum of the dipole which falls along a spiral orbit into the Schwarzschild black hole was found. The characteristic features of this electromagnetic spectrum can be used for determination of the black hole mass. This new way (if implemented) provides higher accuracy of the determination of the black hole mass. Also these features in the spectrum can be used for the determination of the some physical processes in the black hole magnetosphere and in the accretion disk. It is also shown that the asymptotic behavior of this spectrum (at high frequencies) is practically independent from the impact parameter of the falling dipole. [ABSTRACT FROM AUTHOR]

We study a static, spherically symmetric wormhole model whose metric coincides with that of the so-called Ellis wormhole but the material source of gravity consists of a perfect fluid with negative density and a source-free radial electric or magnetic field. For a certain class of fluid equations of state, it has been shown that this wormholemodel is linearly stable under both spherically symmetric perturbations and axial perturbations of arbitrary multipolarity. A similar behavior is predicted for polar nonspherical perturbations. It thus seems to be the first example of a stable wormhole model in the framework of general relativity (at least without invoking phantom thin shells as wormhole sources). [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, we propose a new integral representation for reconstructing the surface density of matter in the flat discs of spiral galaxies. The surface density is expressed through the observed rotation velocity curves of visible matter in the discs of spiral galaxies. The new integral representation is not based on the quadrature of special functions. The solution that is found is used to process and analyse observational data from several spiral galaxies. The new integral representation can be used to more accurately estimate the amount of dark matter in spiral galaxies. [ABSTRACT FROM AUTHOR]

The physical processes that arise when exotic matter accretes onto a charged Reissner-Nordström black hole are considered. Exotic matter is chosen in the form of dust with a negative mass. The various types of horizons and throats that arise in the accretion process are considered. The Einstein equations are integrated analytically by taking into account the contributions from various types of matter (dust and magnetic field). The derived expressions are reduced to a form convenient for their analytical study. Particular solutions of the system are found for a certain class of initial conditions and constraints related to the possibility of dust-layer intersection are investigated. A fundamental change in solution characteristics related to the possibility of black-hole disappearance is found. [ABSTRACT FROM AUTHOR]

Physical processes arising when an impermeable wormhole is irradiated by self-gravitating, exotic radiation are considered. It is shown that, in this case, the conditions required for the passage of signals fromanother universe into our own arise only in our Universe, whereas signals cannot pass through the wormhole in the opposite direction. Such wormholes are called semi-permeable. The stability of a static wormhole filled with radial magnetic field and exotic dust with a negative energy density is also considered. [ABSTRACT FROM AUTHOR]

We consider a model for the passage of radiation through a “wormhole.” A physical interpretation of a special class of solutions of the Einstein equations with a scalar field is given. A solution describing the passage of an infinitely narrow pulse of radiation is constructed by joining along the null geodesic the two stationary equations describing the wormhole before and after the passage of the radiation. The physical consequences of the passage of the radiation on the structure of the wormhole are analyzed. [ABSTRACT FROM AUTHOR]

We consider the hypothesis that some active galactic nuclei and other compact astrophysical objects may be current or former entrances to wormholes (WHs). A broad mass spectrum for astrophysical WHs is possible. We consider various new models of the static WHs including WHs maintained mainly by an electromagnetic field. We also discuss observational effects of a single entrance to WH and a model for a binary astrophysical system formed by the entrances of WHs with magnetic fields and consider its possible manifestation. [ABSTRACT FROM AUTHOR]

We consider models of a wormhole (i) maintained by an electromagnetic field, taking into account quantum vacuum corrections to the equation of state, (ii) maintained by a combination of the magnetic field and phantom energy, with a spherically symmetrical equation of state, and (iii) with a magnetic field and phantom matter with an anisotropic equation of state. It is shown that the quantum corrections and the density and exoticity of phantom energy or matter can be as small as is desired. For an external observer, the entrance to the tunnel appears to be a magnetic monopole of macroscopic size. The accretion of ordinary matter onto the entrance to the tunnel may result in the formation of a black hole with a radial magnetic field. We consider the possibility that some active galactic nuclei and Galactic objects may be current or former entrances to magnetic wormholes. We consider the possible existence of a broad mass spectrum for wormholes, from several billion solar masses to masses of the order of 2 kg. The Hawking effect (evaporation) does not operate in such objects due to the absence of a horizon, making it possible for them to be retained over cosmological time intervals, even if their masses are smaller than 1015 g. We also discuss a model for a binary system formed by the entrances of tunnels with magnetic fields, which could be sources of nonthermal radiation and γ-ray bursts. [ABSTRACT FROM AUTHOR]

A new scheme of sky pixelization is developed for CMB maps. The scheme is based on the Gauss–Legendre polynomials zeros and allows one to create strict orthogonal expansion of the map. A corresponding code has been implemented and comparison with other methods has been done. [ABSTRACT FROM AUTHOR]

We study a scalar hyperbolic partial differential equation, [formula], with nonlinear terms similar to those of the equations of general relativity. The equation has a number of non-trivial analytical solutions whose existence rely on a delicate balance between linear and nonlinear terms. We formulate two classes of second-order accurate central-difference schemes, CFLN and MOL, for numerical integration of this equation. Solutions produced by the schemes converge to exact solutions at any fixed time t when numerical resolution is increased. However, in certain cases integration becomes asymptotically unstable when t is increased and resolution is kept fixed. This behavior is caused by subtle changes in the balance between linear and nonlinear terms when the equation is discretized. Changes in the balance occur without violating second-order accuracy of discretization. We thus demonstrate that a second-order accuracy, althoug necessary for convergence at finite t, does not guarantee a correct asymptotic behavior and long-term numerical stability. Accuracy and stability of integration are greatly improved by an exponential transformation of the unknown variable. [ABSTRACT FROM AUTHOR]

We examined the fall-back disk models, and in general accretion, proposed to explain the properties of AXPs and SGRs. We checked the possibility of some gas remaining around the neutron star after a supernova explosion. We also compared AXPs and SGRs with the X-ray pulsars in X-ray binaries. We conclude that the existing models of accretion from a fall-back disk are insufficient to explain the nature of AXPs and SGRs. [ABSTRACT FROM AUTHOR]

In this paper, timing data for anomalous X-ray pulsars and soft gamma repeaters are compiled. Timing properties of these objects are investigated. The effect of bursts of soft gamma repeaters on their period history is investigated. The P-... diagram for pulsars, X-ray binaries, anomalous X-ray pulsars, soft gamma repeaters and dim radio quiet neutron stars is constructed. The possible evolutionary tracks for anomalous X-ray pulsars, soft gamma repeaters and dim radio quiet neutron stars are examined. [ABSTRACT FROM AUTHOR]

I give a brief review of some problems of the physics of black holes and discuss important new points. I start from the physics outside the black hole's boundary. But probably the problems of the internal structure achievements in our understanding of the nature of the singularity (and beyond) inside a realistic rotating black hole. This presentation also addresses the following questions: Can we see what happens inside a black hole? Can a falling observer cross the singularity without being crushed? An answer to these questions is probably "yes". Finally I discuss some problems of black hole astrophysics. [ABSTRACT FROM AUTHOR]

In this paper we develop a new semi-analytical model of a tidally perturbed or tidally disrupted star proposed recently by two of us. This model is effectively a one-dimensional Lagrangian model and it can be evolved numerically much faster than the conventional three-dimensional (3D) models. A self-consistent derivation of dynamical equations of the model is performed and several important theorems concerning the dynamics of the model are proved without any particular assumptions concerning the equation of state of the stellar gas. The dynamical equations are solved numerically for the case of an n = 1.5 polytropic star evolving in the relativistic tidal field of a 10T-M... Kerr black hole. Some results of these calculations are compared with the results of calculations based on finite-difference 3D simulations. The comparison shows a very good agreement between both approaches to the problem. Then we show that the strength of the tidal encounter depends significantly on the relative orientation of the orbital angular momentum of the star and the spin of the black hole. [ABSTRACT FROM AUTHOR]

Abstract We develop a linear algorithm to extract extragalactic point sources for the Compact Source Catalogue of the upcoming Planck mission. This algorithm is based on a simple top-hat filter in the harmonic domain with an adaptive filtering range which does not require a priori knowledge of the cosmic microwave background power spectrum, and experimental parameters such as the beam size and shape or the pixel noise level. [ABSTRACT FROM AUTHOR]

We discuss some new problems of the modern cosmology which arose after the BOOMERANG and MAXIMA-1 successful missions. Statistics of high peaks of the CMB anisotropy is analyzed and we discuss possible inner structure of such peaks in the observational data of future MAP and PLANCK missions. We have investigated geometrical and statistical properties of the CMB polarization around such high isolated peaks of anisotropy in the presence of a polarized pixel noise and point sources. The structure of polarization fields in the vicinity of singular points with zero polarization is very sensitive to the level of pixel noises and point sources in the CMB maps. [ABSTRACT FROM AUTHOR]

We propose a power filter G[sub p] for linear reconstruction of the CMB signal from onedimensional scans of observational maps. This G[sub p] filter preserves the power spectrum of the CMB signal in contrast to the Wiener filter which diminishes the power spectrum of the reconstructed CMB signal. We demonstrate how peak statistics and a cluster analysis can be used to estimate the probability of the presence of a CMB signal in observational records. The efficiency of the G[sub p] filter is demonstrated on a toy model of an observational record consisting of a CMB signal and noise in the form of foreground point sources. [ABSTRACT FROM AUTHOR]

Analyzes the geometrical and statistical properties of the polarization of the cosmic microwave background (CMB). Singular points of the vector field which describes CMB polarization; Possible signature of primordial gravitational waves in CMB polarization; Methods of analysis of CMB anisotropy and polarization.

We discuss some aspects of the Cosmological Gene Project started at the Special Astrophysical Observatory (Russia) in 1999. The goal of the project is to measure the anisotropy and polarization of the Cosmic Microwave Background (CMB) and investigation of atmospheric fluctuations and foreground on arcmin-scales using the radiotelescope RATAN-600. We develop the cluster analysis of one-dimensional random fields for the application to the RATAN-600 scans. We analyze the specific properties of peak clusterisation in the RATAN-600 scans which to separate the primordial CMB signal from noise. [ABSTRACT FROM AUTHOR]

Geometrical and statistical properties of polarization of CMB are analyzed. Singular points of the vector field which describes CMB polarization are found and classified. Statistical distribution of the singularities is studied. A possible signature of tensor perturbations in CMB polarization is discussed. For a further analysis of CMB statistics, Minkowski functionals are used, which present a technically simple method to search for deviations from a Gaussian distribution. [ABSTRACT FROM AUTHOR]

An analysis is made of the singularities of the polarization field of the cosmic microwave background, where the polarization is equal to zero. It is found that the classification of the singular points differs from the usual three types known in ordinary differential equations. The new statistical properties of the polarization field are discussed, and new methods to detect the presence of primordial tensor perturbations are indicated. © 1999 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Cosmology is currently a broad and rapidly developing field of knowledge. [ABSTRACT FROM AUTHOR]