Showing papers on "Cosmology published in 1983"

The Perturbation Spectrum Evolving from a Nonsingular Initially De-Sitter Cosmology and the Microwave Background Anisotropy

Abstract: Spectra are calculated for the primordial adiabatic perturbations and the gravitational waves that would develop in the author's 1980 model of a nonsingular cosmology with an initial de Sitter quantum stage resulting from gravitational vacuum polarization. The gravitational-wave spectrum will be flat; the adiabatic-perturbation spectrum, nearly so. In that event the most promising way to detect large-scale temperature anisotropy in the cosmic microwave background would be to measure ..delta..T/T correlations over 5/sup 0/--10/sup 0/ angles.

The structure and evolution of the universe

Abstract: Though the kinematics of the evolving universe became known decades ago, research into the physics of processes occurring in the expanding universe received a reliable observational and theoretical basis only in more recent years. These achievements have led in turn to the emergence of new problems, on which an unusually active assault has begun. This second volume of "Relativistic Astrophysics "provides a remarkably complete picture of the present state of cosmology. It is a synthesis of the theoretical foundations of contemporary cosmology, which are derived from work in relativity, plasma theory, thermodynamics, hydrodynamics, and particle physics. It presents the theoretical work that explains, describes, and predicts the nature of the universe, the physical process that occur in it, the formation of galaxies, the synthesis of the light elements, and the cosmological singularity and the theory of gravitation. This book, long and eagerly awaited, is essential for everyone whose work is related to cosmology and astrophysics.

Clustering in a neutrino-dominated universe

Abstract: We have simulated the nonlinear growth of structure in a universe dominated by massive neutrinos using initial conditions derived from detailed linear calculations of earlier evolution. Codes based on a direct N-body integrator and on a fast Fourier transform Poisson solver produce very similar results. The coherencce length of the neutrino distribution at early times is directly related to the mass of the neutrino and thence to the present density of the universe. We find this length to be too large to be consistent with the observed clustering scale of galaxies if other cosmological parameters are to remain within their accepted ranges. The conventional neutrino-dominated picture appears to be ruled out.

Entropy from Extra Dimensions

Abstract: The phenomenon of ''dynamical compactification'' in a universe with 4+n/sub c/ dimensions is studied, and it is found that if the whole process is adiabatic, entropy is pumped into the effective four-dimensional universe. Some cosmological consequences of this fact are discussed.

Nonlinear evolution of large-scale structure in the universe

Abstract: Using N-body simulations we study the nonlinear development of primordial density perturbation in an Einstein--de Sitter universe. We compare the evolution of an initial distribution without small-scale density fluctuations to evolution from a random Poisson distribution. These initial conditions mimic the assumptions of the adiabatic and isothermal theories of galaxy formation. The large-scale structures which form in the two cases are markedly dissimilar. In particular, the correlation function xi(r) and the visual appearance of our adiabatic (or ''pancake'') models match better the observed distribution of galaxies. This distribution is characterized by large-scale filamentary structure. Because the pancake models do not evolve in a self-similar fashion, the slope of xi(r) steepens with time; as a result there is a unique epoch at which these models fit the galaxy observations. We find the ratio of cutoff length to correlation length at this time to be lambda/sub min//r/sub 0/ = 5.1; its expected value in a neutrino dominated universe is 4(..cap omega..h)/sup -1/ (H/sub 0/ = 100h km s/sup -1/ Mpc/sup -1/). At early epochs these models predict a negligible amplitude for xi(r) and could explain the lack of measurable clustering in the Ly..cap alpha.. absorption lines of high-redshift quasars. However, large-scale structuremore » in our models collapses after z = 2. If this collapse precedes galaxy formation as in the usual pancake theory, galaxies formed uncomfortably recently. The extent of this problem may depend on the cosmological model used; the present series of experiments should be extended in the future to include models with ..cap omega..<1.« less

Possible Astronomical Effects of Mirror Particles

Abstract: A discussion is given of the astronomical implications of a model wherein every elementary particle would have a corresponding mirror (M-) particle of the same mass, and to each interaction (strong, weak, electromagnetic) there would correspond an M-interaction Ordinary (O-) and M-particles could interact essentially only by gravitation As the model properties are strictly symmetric, so also would be the cosmological evolution of O- and M-matter Qualitative consideration of how M-irregularities would evolve in the early universe suggests that on mass scales M< or approx =10/sup 6/ M/sub sun/ there will be practically no mixing of O- and M-matter except by accretion The model can be tested by improving the observational data on the primordial helium abundance, the missing mass in the galactic disk, and perhaps the nonradial oscillations of the sun

The large-scale structure of the universe

Abstract: A survey is given of theories for the origin of large-scale structure in the universe: clusters and superclusters of galaxies, and vast black regions practically devoid of galaxies. Special attention is paid to the theory of a neutrino-dominated universe—a cosmology in which electron neutrinos with a rest mass of a few tens of electron volts would contribute the bulk of the mean density. The evolution of small perturbations is discussed, and estimates are made for the temperature anisotropy of the microwave background radiation on various angular scales. The nonlinear stage in the evolution of smooth irrotational perturbations in a lowpressure medium is described in detail. Numerical experiments simulating large-scale structure formation processes are discussed, as well as their interpretation in the context of catastrophe theory.

The evolution of structure in the universe from axions

Abstract: A scenario where axions provide the dark matter in the universe is considered. Fluctuations in the axion field density produced by domain walls and strings cause the appearance of axion clumps of masses of order 10 to the 6th power solar mass which most likely collapse to black holes by or at the time that the universe becomes axion dominated at T is approximately 10 eV. These objects form the building blocks for a clustering hierarchy theory of galaxy and supercluster formation on scales up to approximately 10 Mpc and approximately 10 to the 15th power solar mass.

Implications of a Class of Grand Unified Theories for Large Scale Structure in the Universe

Abstract: A class of grand unified theories in which cosmologicaly significant axion and neutrino energy densities arise naturally is discussed. To obtain large scale structure three scenarios are considered: (1) an inflationary scenario; (2) inflation followed by string production; and (3) a non-inflationary scenario with density fluctuations caused solely by strings. Inflation may be compatible with the recent observational indications that mega 1 on the scale of superclusters, particularly if strings are present.

Alignment of faint galaxy images: cosmological distortion and rotation

Abstract: We have examined the images of 44,462 randomly chosen galaxies between 22.5 and 23.5 J apparent magnitude in 35 fields for a coherent ellipticity due to cosmological image distortion arising from inhomogeneity and anisotropy in the large-scale mass distribution of the universe. Galaxy alignments would also be expected in a rotating universe, due to vorticity. Our result for a large-scale ellipticity is null with a 3 sigma upper limit of e/sub max/<0.04 out to a redshift of 0.6, implying that the cosmological distortion is small out to redshifts approx.1. Variations of the field-to-field ellipticity ..delta..e over the sky have a dispersion of ..delta..e<0.03. This sets a 3 sigma upper limit of ..cap omega delta..rho/rho<0.1 for the mass overdensity contrast in clusters of 10/sup 3/ Mpc size, and a 3 sigma upper limit to the Weyl tensor components of approx.1.5 x 10/sup -20/ yr/sup -2/. Connection with the large- and small-scale cosmic microwave background anisotropy is discussed. Our 3 sigma upper limit for the quadrupole moment of the ellipticity is 0.07.

Cluster analysis of the nonlinear evolution of large-scale structure in an axion/gravitino/photino-dominated universe

Abstract: The authors consider nonlinear evolution of the inflationary scale-free spectrum of adiabatic density perturbations in (1) a neutrino-dominated universe (sharp short-wavelength cutoff), and (2) an axion-, gravitino-, or photino-dominated universe (some small-scale power) In (2) galaxy formation begins long before the present (as defined by covariance function), resolving a possible problem in (1) Both models are found to be acceptable upon cluster analysis The authors believe that a new picture, based on (2), merits consideration

Theory of Matter and Cosmology in William Gilbert's De magnete

Abstract: ILLIAM GILBERT, the author of De magnete (1600) and the acknowledged father of magnetic and electrical sciences, has been the object of conflicting views: where some have discerned the first experimental philosopher, the \"transcendent genius\" of \"a marvelous originality of thought,\" others have seen nothing but \"a moderate peripatetic\" whose \"philosophy of nature does not move far from scholastic philosophy, except away from its logical consistency.\"1 Indeed, Gilbert's work can give the impression that his experimental method and his positive magnetic and electrical discoveries contrast with what might appear to be a backward-looking hodgepodge of Peripatetic and animistic philosophies of nature. In this paper I shall concentrate on Gilbert's theory of matter in order to show both how it evolved gradually out of the postulate that the (magnetic) earth was rotating and how far it in fact departed from the Peripatetic elemental theory. Gilbert's was the first seventeenth-century physics compatible with a non-Ptolemaic cosmology, and it succeeded fairly well in accounting for many important relevant phenomena. Although it still conformed to some metatheoretical notions of Aristotelian physics, its concepts cut across received distinctions and classifications. The traditional aspect of the theory is largely due to Gilbert's continued usage of scholastic terms, many of which he endowed, however, with new meanings. This Peripatetic vocabulary was liable to mislead not only modern historians, but also Gilbert's contemporaries. In this study, therefore, I try to reconstruct both the course of Gilbert's own thinking and the impressions his affirmations made on contemporary ears, informed by Peripatetic, Paracelsian, or alchemical thought. I shall limit the analysis to De magnete, whose lack of influence on the theory of matter, to which it was highly relevant, I shall try to explain.2

Density fluctuations from strings and galaxy formation

Abstract: The spectra of density fluctuations caused by strings in a universe dominated either by baryons, neutrinos, or axions are presented. Realistic scenarios for galaxy formation seem possible in all three cases. Examples of grand unified theories which lead to strings with the desired mass scales are given.

Inflation and time asymmetry in the Universe

Abstract: The recently proposed inflationary Universe scenario1–4 explains several of the mysteries of modern cosmology. I argue here that it also provides a natural explanation for the origin of time asymmetry (‘time's arrow’) in the Universe. The new feature which inflation injects into this long-standing problem is the temporary dominance of the cosmological term in the gravitational field equations, which acts as a sort of repulsive gravity. This term generates huge quantities of energy and radiation (or matter) entropy, while drastically reducing the entropy density of the gravitational field. It thus establishes a large gap between the radiation entropy and the gravitational entropy, which gravity is now trying to close.

The structure and expansion law of a shock wave in an expanding universe

Abstract: The structure and expansion law of a shock wave, generated by explosions of pregalactic objects or young galaxies in the early universe, is investigated with specific consideration of the expansion of the ambient medium. First, an asymptotic solution for adiabatic explosions is obtained by numerical integration of the similarity solution. Time-dependent numerical solutions and analytic approximation are presented for the more general case. Then radiative and Compton cooling are included in numerical studies of expanding shocks. Finally, some comments on the structure of intergalactic medium are presented.

An upper limit on the stochastic background of ultralow frequency gravitational waves

Abstract: Using pulse arrival time data for PSR 1237+25, a pulsar with unusually regular timing behavior, we place a firm upper limit on the magnitude of any stochastic background of low-frequency gravitational radiation in the universe. At frequencies between 0.3 x 10/sup -8/ Hz, the equivalent energy density limits are well below those needed to close the universe on account of gravitational waves alone.

Structure of the cosmic microwave background

Abstract: We predict the structure expected in the cosmic microwave background over large angular scales in realistic anisotropic and inhomogeneous universes. In a homogeneous anisotropic universe we find that there exist two possibilities, a quadrupole or a hotspot pattern with and without dipole contributions. A hotspot allows a direct observational test of an open universe. We show how infinite wavelength inhomogeneous perturbations of the Friedman universe can be represented as ensembles of different homogeneous universes.

Fragmentation of the universe

Abstract: We have tested the hypothesis that the universe underwent a single fragmentation event, separating into protogalactic volumes at a relatively early stage after the Big Bang. Assuming that the present total luminosity of each galaxy is proportional to its mass, we plotted the number and mass distribution of a thousand nearby galaxies just as we would in an analysis of fragments from a laboratory high-explosive experiment. The results are consistent with the single-fragmentation hypothesis.

Theory of Superdense Matter and Degenerate Stellar Configurations

Abstract: During the last two decades the theory of degenerate stellar configurations has been developed in works by Ambartsumian and Sahakian, as well as in some other papers. This article is further progress in this direction.

The evolution of voids in the expanding universe

Abstract: We examine the growth and nonlinear evolution of spherically symmetric, negative density perturbations in an otherwise uniform Friedmann cosmology. In general, the cavity expands and its density relative to the background decreases. In certain cases, the cavity comes to be surrounded by a narrow shell of matter with a density substantially greater than the mean cosmological value; we show that such an overdense shell can form even when no overdense region is present anywhere in the initial density profile. These ''walled-in'' cavities may be identified with recently observed, large-scale holes in the galaxy distribution, and the shells themselves with the superclusters which define the boundaries of such holes. However, we also show that there exist choices for the initial density profile which lead to the formation of deep cavities which are not surrounded by any overdense shells. We examine the behavior of the shell-growth phenomenon under various assumptions about the background universe and the initial density perturbation, and find that shell growth is enhanced for high values of the density parameter ..cap omega.., positive (repulsive) cosmological constant, steep density profile of the initial perturbation, large-amplitude perturbation, and/or early origin of the perturbation. We derive analytic criteria for classifying arbitrary initiallymore » negative density profiles to determine (a) whether shell crossing with formally infinite density will eventually occur for any given comoving mass coordinate, and (b) whether matter at adjacent mass coordinates will form a shell of finite overdensity which persists indefinitely.« less