arXiv subjects

Igor D. Novikov

Publications and source records attributed to Igor D. Novikov.

15 recordsLinked to original sources

arXiv2023

Uniform sky glow (CMB) observed through the throat of a wormhole

The problem of the possibility of observing a uniform sky glow through the throat of a Morris--Thorne wormhole by an observer located in another asymptotically flat space-time is considered. It is shown that an individual star has multiple images, and the image of a luminous sky has a complex structure and contains ring structures. The reasons for the emergence of such structures are considered. The distribution of radiation intensity in the image along the radial coordinate is constructed.In addition, an image of the Morris-Thorne wormhole was constructed against the background of uniform sky radiation in the observer's space. A comparison to observations can be made by producing a synthetic Morris-Thorne type wormhole image against a CMB background. This image has been constructed by a combination of the images for inner and outer areas.

gr-qc↗

arXiv2022

Silhouettes of wormholes traversed for radiation

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.

gr-qc↗

arXiv2021

Gravitational lensing and wormhole shadows

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

gr-qc↗

arXiv2020

Comparison of the spatial properties of entrances to black holes and wormholes

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.

gr-qc↗

arXiv2018

Shadow of rotating black holes on a standard background screen

We present the shape of the black hole shadow on the standard background screen as it is registered by the distant observer. The screen is an infinite plane, emitting the quanta uniformly distributed to a hemisphere. The source of emission is considered to be optically thin and optically thick. It is shown that the shape of a black hole shadow depends crucially on the angle between the plane and the view line to the distant observer. The shadow shapes for the different values of this angle are also presented. Both Schwarzschild and Kerr metrics are considered.

gr-qc↗

arXiv2009

Homogeneous singularities inside collapsing wormholes

We analyze analytically and numerically the origin of the singularity in the course of the collapse of a wormhole with the exotic scalar field Psi with negative energy density, and with this field Psi together with the ordered magnetic field H. We do this under the simplifying assumptions of the spherical symmetry and that in the vicinity of the singularity the solution of the Einstein equations depends only on one coordinate (the homogeneous approximation). In the framework of these assumptions we found the principal difference between the case of the collapse of the ordinary scalar field Phi with the positive energy density together with an ordered magnetic field H and the collapse of the exotic scalar field Psi together with the magnetic field H. The later case is important for the possible astrophysical manifestation of the wormholes.

gr-qc↗

arXiv2009

The Gauss-Legendre Sky Pixelization for the CMB polarization (GLESP-pol). Errors due to pixelization of the CMB sky

We present developing of method of the numerical analysis of polarization in the Gauss--Legendre Sky Pixelization (GLESP) scheme for the CMB maps. This incorporation of the polarization transforms in the pixelization scheme GLESP completes the creation of our new method for the numerical analysis of CMB maps. The comparison of GLESP and HEALPix calculations is done.

astro-ph.CO↗

arXiv2005

Correlations from Galactic foregrounds in the 1-year Wilkinson Microwave Anisotropy Probe WMAP data

We study a specific correlation in spherical harmonic multipole domain for cosmic microwave background (CMB) analysis. This group of correlation between Δl=4n, n=1,2... is caused by symmetric signal in the Galactic coordinate system. An estimator targeting such correlation therefore helps remove the localized bright point-like sources in the Galactic plane and the strong diffused component down to the CMB level. We use 3 toy models to illustrate the significance of these correlations and apply this estimator on some derived CMB maps with foreground residuals. In addition, we show that our proposed estimator significantly damp the phase correlations caused by Galactic foregrounds. This investigation provides the understanding of mode correlations caused by Galactic foregrounds, which is useful for paving the way for foreground cleaning methods for the CMB.

astro-ph↗

arXiv2005

"4n multipole periodicity" of the Galaxy image in the WMAP data

We present a specific periodicity of the Galaxy images in the multipole domain which can be used for separation of the cosmic microwave background (CMB) signal from the Galaxy and foreground component. This method takes into consideration all the coefficients of the expansion of the signal from the sky ΔT(Θ, ϕ) into spherical harmonics and dealing with combination of multipoles a_{l,m} and a_{l+Δ,m} for each multipole mode (\ell, -\ell \le m \le \ell) from the whole sky without galactic cut, masks or any dissection of the whole sky into disjoint regions. For the polar coordinate system we use particular values for Δ=4n, n=1,2,... which remove all bright point-like sources localized in the Galactic plane and strong diffused component down to the CMB level. To illustrate that significant correlations of the point like sources and foregrounds a_{l,m},a_{l+Δ,m} coefficients we apply this method to the WMAP Q,V and W bands in order to remove these marks of Galaxy from the maps. We believe that our method would be useful for separation of the CMB signal from different kind of "noises" in the maps.

astro-ph↗

arXiv2004

Foreground analysis from the 1-year Wilkinson Microwave Anisotropy Probe (WMAP) data

We present a detailed analysis on the phases of the WMAP foregrounds (synchrotron, free-free and dust emission) of the WMAP K-W bands in order to estimate the significance of the variation of the spectral indices at different components. We first extract the spectral-index varying signals by assuming that the invariant part among different frequency bands have 100% cross-correlation of phases. We then use the minimization of variance, which is normally used for extracting the CMB signals, to extract the frequency independent signals. Such a common signal in each foreground component could play a significant role for any kind of component separation methods, because the methods cannot discriminate frequency independent foregrounds and CMB.

astro-ph↗

arXiv2003

Phase analysis of the 1-year WMAP data and its application for the CMB foreground separation

We present a new method based on phase analysis for the Galaxy and foreground component separation from the cosmic microwave background (CMB) signal. This method is based on a prevailing assumption that the phases of the underlying CMB signal should have no or little correlation with those of the foregrounds. This method takes into consideration all the phases of each multipole mode (l <= 50, -l <= m <=l) from the whole sky without galactic cut, masks or any dissection of the whole sky into disjoint regions. We use cross correlation of the phases to illustrate that significant correlations of the foregrounds manifest themselves in the phases of the WMAP 5 frequency bands, which are used for separation of the CMB from the signals. Our final phase-cleaned CMB map has the angular power spectrum in agreement with both the WMAP result and that from Tegmark, de Oliveira-Costa and Hamilton (TOH), the phases of our derived CMB signal, however, are slightly different from those of the WMAP Internal Linear Combination map and the TOH map.

astro-ph↗

arXiv2003

Developments in General Relativity: Black Hole Singularity and Beyond

At the 20-th Texas Symposium on Relativistic Astrophysics there was a plenary talk devoted to the recent developments in classical Relativity. In that talk the problems of gravitational collapse, collisions of black holes, and of black holes as celestial bodies were discussed. But probably the problems of the internal structure of black holes are a real great challenge. In my talk I want to outline the recent 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".

gr-qc↗

arXiv2000

Three-Dimensional Billiards with Time Machine

Self-collision of a non-relativistic classical point-like body, or particle, in the spacetime containing closed time-like curves (time-machine spacetime) is considered. A point-like body (particle) is an idealization of a small ideal elastic billiard ball. The known model of a time machine is used containing a wormhole leading to the past. If the body enters one of the mouths of the wormhole, it emerges from another mouth in an earlier time so that both the particle and its "incarnation" coexist during some time and may collide. Such self-collisions are considered in the case when the size of the body is much less than the radius of the mouth, and the latter is much less than the distance between the mouths. Three-dimensional configurations of trajectories with a self-collision are presented. Their dynamics is investigated in detail. Configurations corresponding to multiple wormhole traversals are discussed. It is shown that, for each world line describing self-collision of a particle, dynamically equivalent configurations exist in which the particle collides not with itself but with an identical particle having a closed trajectory (Jinnee of Time Machine).

gr-qc↗

arXiv2000

Decoherence Caused by Topology in a Time-Machine Spacetime

Non-relativistic quantum theory of non-interacting particles in the spacetime containing a region with closed time-like curves (time-machine spacetime) is considered with the help of the path-integral technique. It is argued that, in certain conditions, a sort of superselection may exist for evolution of a particle in such a spacetime. All types of evolution are classified by the number $n$ defined as the number of times the particle returns back to its past. It corresponds also to the topological class of trajectories of the particle. The evolutions corresponding to different values of $n$ are non-coherent. The amplitudes corresponding to such evolutions may not be superposed. Instead of one evolution operator, as in the conventional (coherent) description, evolution of the particle is described by a family $U_n$ of partial evolution operators. This is done in analogy with the formalism of quantum theory of measurements, but with essential new features in the dischronal region (the region with closed time-like curves) of the time-machine spacetime. Partial evolution operators $U_n$ are equal to integrals over the topological classes of paths if the evolution begins and ends in the chronal regions. If the evolution begins or/and ends in the dischronal region, the integral over the topological class should be multiplied by a certain projector to give the partial evolution operator $U_n$. Thus defined partial evolution operators possess the property of generalized unitarity and multiplicativity. The part of evolution containing repeated returning backward in time cannot be factorized: all backward passages of the particle have to be considered as a single act, that cannot be presented as gradually, step by step, passing through `causal loops'.

gr-qc↗

arXiv2000

On the Structure of Advective Accretion Disks At High Luminosity

Global solutions of optically thick advective accretion disks around black holes are constructed. The solutions are obtained by solving numerically a set of ordinary differential equations corresponding to a steady axisymmetric geometrically thin disk. We pay special attention to consistently satisfy the regularity conditions at singular points of the equations. For this reason we analytically expand a solution at the singular point, and use coefficients of the expansion in our iterative numerical procedure. We obtain consistent transonic solutions in a wide range of values of the viscosity parameter alpha and mass acretion rate. We compare two different form of viscosity: one takes the shear stress to be proportional to the pressure, while the other uses the angular velocity gradient-dependent stress. We find that there are two singular points in solutions corresponding to the pressure-proportional shear stress. The inner singular point locates close to the last stable orbit around black hole. This point changes its type from a saddle to node depending on values of alpha and accretion rate. The outer singular point locates at larger radius and is always of a saddle-type. We argue that, contrary to the previous investigations, a nodal-type inner singular point does not introduce multiple solutions. Only one integral curve, which corresponds to the unique global solution, passes simultaneously the inner and outer singular points independently of the type of inner singular point. Solutions with the angular velocity gradient-dependent shear stress have one singular point which is always of a saddle-type and corresponds to the unique global solution. The structure of accretion disks corresponding to both viscosities are similar.

astro-ph↗