Hydrogen recombination in an expanding universe

Leningrad State University; Special Astrophysical Observatory, USSR Academy of Sciences. Translated from Astrofizika, Vol. 34, No. 2, pp. 249–264, March–April, 1991.     

Gravitational clustering of galaxies in an expanding universe

We inquire the phenomena of clustering of galaxies in an expanding universe from a theoretical point of view on the basis of thermodynamics and correlation functions. The partial differential equation is developed both for the point mass and extended mass structures of a two-point correlation function by using thermodynamic equations in combination with the equation of state taking gravitational interaction between particles into consideration. The unique solution physically satisfies a set of boundary conditions for correlated systems and provides a new insight into the gravitational clustering problem.     

The stochastic behaviour of a galactic model dynamical system

We study the stochastic behaviour of a time-independent dynamical system that has closed zero velocity curves for arbitrarily large energies. Thus no escapes appear in such a system and we can study the stochasticity of the system for any value of the energy. The numerical results show that the degree of stochasticity grows as the energy increases from zero, but then it reaches a maximum and for still larger energies it decreases slowly.     

Concerning the instantaneous mass and the extent of an expanding universe

In this article we want to answer the cosmologically relevant question what, with some good semantic and physical reason, could be called the massM _u of an infinitely extended, homogeneously matter‐filled and expanding universe. To answer this question we produce a space‐like sum of instantaneous cosmic energy depositions surrounding equally each spacepoint in the homogeneous universe. We calculate the added‐up instantaneous cosmic energy per volume around an arbitrary space point in the expanding universe. To carry out this sum we use as basic metrics an analogy to the inner Schwarzschild metric applied to stars, but this time applied to the spacepoint‐related universe. It is then shown that this leads to the added‐up proper energy within a sphere of a finite outer critical radius defining the point‐related infinity. As a surprise this radius turns out to be reciprocal to the square root of the prevailing average cosmic energy density. The equivalent mass of the universe can then also be calculated and, by the expression which is obtained here, shows a scaling with this critical radius of this universe, a virtue of the universe which was already often called for in earlier works by E. Mach, H. Thirring and F. Hoyle and others. This radius on the other hand can be shown to be nearly equal to the Schwarzschild radius of the so‐defined mass M _u of the universe. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Formation of galaxies in the expanding universe

The possibility of the formation of galaxies both during the galactic clustering of small structural units originated earlier and at fragmentation of larger formations is considered. A selfsimilar spectrum of long-wave perturbations is obtained. The results of numerical calculations and conclusions of Press and Schechter's (1974) work are discussed.Translated by Miss Eva Vokálová, Astronomical Institute of Charles University, Prague.     

Mach–poincaré gravodynamics and condensation phenomena in an expanding universe

We discuss the condensation phenomena in a very simple model, which allows for transparent calculations. We compare the condensation times of subsystems decoupled from the cosmological expansion in different approaches to Mach-Poincaré gravodynamics with Newtonian mechanics. In all cases contracting subsystems without inner rotation collapse, only the time-scales differ.     

Propagation of a burst of radiation in an expanding and recombining universe: Thomson scattering

The propagation of an instantaneous burst of nonpolarized isotropic radiation from the time of its onset at some redshift z ₀ to the time of its recording at the present epoch is considered within the framework of a flat cosmological model. Thomson (Rayleigh) scattering by free electrons is believed to be the only source of opacity. The spatial distributions of the mean (over the directions) radiation intensity as well as the angular distributions of the radiation intensity and polarization at various distances from the burst center have been constructed. The mean intensity profile normalized to the total number of photons emitted during the burst is shown to depend weakly on the initial conditions (the burst time z ₀, the width and shape of the initial radiation distribution) at fairly high z ₀ (≥1400). As regards the angular intensity and polarization distributions, they turn out to be rather narrow (3–10 arcmin), while the polarization can reach 70%. On average, the expected polarization can be about 15%.     

Magnetohydrodynamic effects on the growth of condensations in an expanding universe and the formation of galaxies

We review evidence for the existence of the Galaxy's (Milky Way's) magnetic field and the evidence for an intergalactic magnetic field permeating an ionized inter-galactic medium. The magnetohydrodynamics of such an inter-galactic medium during the post-recombination expansion and the effects of MHD on the formation of galaxies are then considered: isotropic cosmologies, the interaction of magnetic fields with isotropic backgrounds, detailed MHD perturbation computations, and an analysis of related MHD galaxyformation studies.     

Effect of dynamical cosmological constant in presence of modified Chaplygin gas for accelerating universe

In this paper we have considered the Universe to be filled with Modified Gas and the Cosmological Constant Λ to be time-dependent with or without the Gravitational Constant G to be time-dependent. We have considered various phenomenological models for Λ, viz., and . Using these models it is possible to show the accelerated expansion of the Universe at the present epoch. Also we have shown the natures of G and Λ over the total age of the Universe. Using the statefinder parameters we have shown the diagrammatical representation of the evolution of the Universe starting from radiation era to ΛCDM model.     

A static model of the universe

It is shown that the observational data of cosmology and the universe evolution can be explained in the framework of static (non-expanding) models of the universe without singularity by introducing in the time part of the metrics the scale factor, dependent on time. The latter can be interpreted as a function of the light velocity evolution or the rate of cosmic time relative to the linear atomic time.Expressions for these functions have been obtained on the basis of the Einstein equation solution with the use of conformal metrics.The theory is consistent with the test of dependence of the angular galaxy dimension on the redshift.     

The Einstein static model of the universe as a whole

The Einstein static model of the universe as a whole is considered in Euclidean space and absolute time of a privileged reference frame. The universe as a whole is stable that specifies observers at rest relative to the global space of the universe. An observer in the centre of the universe is assumed to experience downward inertial acceleration along a certain radius due to the kinetic energy of the universe, with the total acceleration over all radii being equal zero. This yields the Doppler effect for the photon coming from the distant source that may explain the Hubble law in the static universe. The predictions of the model are qualitatively in agreement with the observations in the cosmological tests of a standard candle and a standard rod. Explanation of stretching of the light curve of SN Ia is proposed within the model considered.     

Accretion of holographic dark energy: dependency only upon horizon radius of expanding universe

In this paper we deal with accretion of dark energy in the holographic dark energy model for a general non-rotating static spherically symmetric black hole. The mass of the black hole increases or decreases depending on the nature of the holographic dark energy (quintessence or phantom) as well as on some integration parameters. It is to be illustrated that the enhancement or reduction of mass of a black hole is independent of the mass or size of the black hole itself. Rather it depends only upon the radius of the event horizon of the universe. Finally, the generalized second law of thermodynamics has been studied on the event horizon to be assured that the law holds even if when the black hole mass is decreasing though it is engrossing some mass.     

The Jeans's instability in an expanding medium

In this paper we solve, by the two time-scale method, the equation governing the evolution of a density perturbation in any expanding medium. The surprisingly simple result we obtain allows an accurate insight into the role played by cumulative but contradictory effects such as gravitational attraction forces and the expanding velocity field. Although the existence of a critical length is confirmed, there is no catastrophic growth of instability.     

Binaries in the universe. possible dynamical mechanisms of formation,evolution and disruption of different kinds of constituents of the universe

We study the dynamics of extended shells of relatively low-mass particles around and inside the orbit of two heavy centres of gravity (a binary) by computer simulations. The binary components are surrounded byN = 16 000 small mass particles in uniform random distribution on few spherical envelopes with different radii expanding with respective velocities. Some shells are inside the orbit of binary.We apply this model to binary galaxy systems with baryonic dark matter, e.g., massive black holes. In principle, we can apply this model to different kinds of objects (from binary star systems until superclusters of galaxies).It is shown that the shell expands homologously with a decreasing velocity and then, falls back into the binary system forming zones of compressed matter. At some moment of time there could be a collapse of these particles on to the heavier component of the binary. Further in time, some part of particles which were outside the binary orbit escape from the system. Other particles which were initially inside of the orbit are captured by binary components.We consider a number of different models with different initial parameters. For models with smaller radii of shells, about one-half of the particles escape from systems; whereas for larger values the shell disrupts as a whole. Escaping particles form collimated flows in planes of orbits of binaries. Positions of flows and directions of motion depend on positions of heavier components of binaries at the moment of a closest approach of particles and on ratios of masses of binary components.We show that during evolution of our models different kinds of structures of systems often are very similar to the observed structures of galaxies: spiral and elliptical galaxies, interacting galaxies, different kinds of flows and jets. Totally systems are expanding - after 40 periods of rotation of the binary the system expands by 300 times.     

Formation of difference in distribution between visible and invisible matters in the expanding universe

The visible and invisible matters in the universe have rather different density distributions. The formar is obvious clustered on the scales of galaxies, clusters and superclusters, while the latter is rather more uniform. Here we discuss the possibility of this difference forming during the stage of Jeans clustering. For a two-component universe, so long as the growth and decay time-scales of gravitational perturbation satisfy a certain relation, the perturbation will grow in one component and decay in the other. Specific calculations are made for the development of inhomogeneity in a universe consisting of two collisionless gases. It is found that as long as the densities of the Jeans lengths of the two components satisfy the relations ?₁ ? ?₂λ_1j ? λ_2j, then, whether the initial perturbation is in component 1 or component 2, the result will be component 1 having a large degree of inhomogeneity and component 2, a small one. If the invisible matter is mainly neutrino with a finite rest-mass, then the above result can be used to explain the quasi-uniform distribution of the invisible matter.     

A two-component model for the large-scale structure of the universe

I consider a two-component model for the distribution of galaxies and their aggregates, a self-similar compoent with a fractal structure and a random component. From the normalization of the observed correlation function, the ratio of the two components is estimated to be 1:4.     

Report on the dynamical evolution of an axially symmetric quasar model

The role of the angular momentum in the regular or chaotic character of motion in an axially symmetric quasar model is examined. It is found that, for a given value of the critical angular momentumL _zc , there are two values of the mass of the nucleusM _n for which transition from regular to chaotic motion occurs. The [L _zc – M _n ] relationship shows a linear dependence for the time independent model and an exponential dependence for the evolving model. Both cases are explained using theoretical arguments together with some numerical evidence. The evolution of the orbits is studied, as mass is transported from the disk to the nucleus. The results are compared with the outcomes derived for galactic models with massive nuclei.