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At least 1,063 records · Page 59
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NASA NTRS1986

Monopoles, cosmology, and astrophysics - Update 1985

The characteristics of the superheavy magnetic monopoles (MMs) predicted by GUTs are reviewed, and recent developments in astrophysical MM search techniques are surveyed. Theoretical models of the birth, current distribution, and motion of MMs are examined; the observational implications of MM mass, magnetic charge, and ability to catalyze nucleon decay are considered; estimates of the average and local flux limits for MMs of 10 to the 25th eV are given (less than about 3 x 10 to the -15th and less than about 3 x 10 to the -11th/sq cm sr sec, respectively); and the possibility of detecting MMs in the sun (if they can escape annihilation there) is discussed.

Turner, Michael S.↗
NASA NTRS1987

Gauge invariant quantum cosmology

The study of boundary conditions, the Hamiltonian constraint, reparameterization-invariance, and quantum dynamics, is presently approached by means of the path-integral quantization of minisuperspace models. The separation of the wave functions for expansion and contraction by the Feynman boundary conditions is such that there can be no interference between them. This is implemented by the choice of a contour in the complex plane, in order to define the phase of the square-root Arnowitt, Deser, and Misner (1960) Hamiltonian for expansion, collapse, and the classically forbidden region.

Berger, Beverly K.↗
NASA NTRS1987

Helium diffusion in stars and the value of the cosmological constant

The effect of He diffusion on the evolution of stars is to speed it up by increasing the mean atomic weight at the center, thereby minimizing the apparent conflict between the great ages of globular clusters and the age of the universe, as arrived at via the Hubble constant. Attention is presently given to the consequences of work on this effect by Noerdlinger and Arrigo (1980) and Stringfellow et al. (1983), implying that Tayler's (1986) estimate for globular clusters of 16 Gyr should be reduced to 13 Gyr.

Noerdlinger, Peter↗
NASA NTRS1987

Cosmological implication of a new measurement of the submillimeter background radiation

A new submillimeter measurement of the cosmic background radiation (T. Matsumoto et al., 1988) reveals excess brightness between 1000 and 300 microns. The excess corresponds to about 10 percent of the undistorted blackbody radiation. The observed excess is consistent with thermal emission from dust with a relative density of 0.0001-0.00001, if the dust is heated at a redshift z of about 10-40.

Hayakawa, Satio↗
NASA NTRS1987

X-ray surveys as tools to investigate the cosmological evolution of quasars, BL Lac objects and clusters of galaxies

A progress report on a major extension of the Einstein Observatory Medium Sensitivity Survey (MSS) is presented. The MSS consists of X-ray sources serendipitously discovered with the IPC on board the Einstein Observatory in the energy range 0.3-3.5 keV, at fluxes between 10 to the -11th and 10 to the -13th ergs/sq cm/s. The basic properties of the extragalactic sources identified with AGN and clusters of galaxies are discussed.

Gioia, Isabella M.↗
NASA NTRS1988

Cosmological structure formation from soft topological defects

Some models have extremely low-mass pseudo-Goldstone bosons that can lead to vacuum phase transitions at late times, after the decoupling of the microwave background.. This can generate structure formation at redshifts z greater than or approx 10 on mass scales as large as M approx 10 to the 18th solar masses. Such low energy transitions can lead to large but phenomenologically acceptable density inhomogeneities in soft topological defects (e.g., domain walls) with minimal variations in the microwave anisotropy, as small as delta Y/T less than or approx 10 to the minus 6 power. This mechanism is independent of the existence of hot, cold, or baryonic dark matter. It is a novel alternative to both cosmic string and to inflationary quantum fluctuations as the origin of structure in the Universe.

Hill, Christopher T.↗
NASA NTRS1988

Atlas of Galaxies Useful for Measuring the Cosmological Distance Scale

A critical first step in determining distances to galaxies is to measure some property of primary objects such as stars of specific types, H II regions, and supernovae remnants that are resolved out of the general galactic star content. With the completion of the Mount Wilson/Palomar/Las Campanas survey of bright galaxies in 1985, excellent large-scale photographs of the complete Shapley-Ames sample were on hand. Most of the galaxies useful for distance scale calibration are in this collection. This atlas contains photographs of 322 galaxies including the majority of all Shapley-Ames bright galaxies, plus cluster members in the Virgo Cluster core that might be usefully resolved by the Hubble Space Telescope (HST). Because of crowding and high background-disk surface brightness, the choice of field position is crucial for programs involving resolution of particular galaxies into stars. The purpose of this atlas is to facilitate this choice. Enough information is given herein (coordinates of the galaxy centers and the scale of the photography) to allow optimum placement of the HST wide-field planetary camera format of approximately 150 arc-seconds on a side.

Sandage, Allan↗
NASA NTRS1989

Solitosynthesis: Cosmological evolution of non-topological solitons

The thermal creation, fusion, evaporation, and destruction of non-topological solitons (NTS) after a phase transition in the early universe is considered. By defining and following NTS statistical equilibrium and departures from it, and depending on particle physics parameters, one of three possible scenarios occurs. If reaction rates are high enough, a period of equilibrium occurs and relic abundances are determined by the freeze-out temperature. Equilibrium first drives most NTS's into their constituents (free phi particles) and then causes rapid fusion into large NTS's. If freeze-out occurs during the first phase, the NTS's are almost entirely destroyed, while if it occurs during the second phase, solitosynthesis occurs and NTS's may be cosmically relevant. For slow reaction rates the NTS's are born frozen out and have the abundance determined by the phase transition. Analytic approximations for determining the abundances are developed, and tested by numerically integrating a reaction network in an expanding universe. Unfortunately, for most of the parameter space considered, solito-destruction/evaporation occurs.

Griest, Kim↗
NASA NTRS1988

Infrared cosmology from space

The potential scientific impact of the Space Infrared Telescope Facility (SIRTF) on studies of high-redshift phenomena and the evolution of the universe is discussed. Several observational programs are described: (1) studies of very high redshift objects and their absorption spectra, and what they reveal about pregalactic gas and galaxy formation; (2) a large high-redshift galaxy survey for studying the evolution of galaxy clustering at z about 1 to 2; (3) generating a statistically complete catalog of several hundred gravitational lens systems; and (4) studies of the spectrum and anisotropy of the far-infrared background and what it reveals about the nature and distribution of pregalactic stars, gas, and dust.

Hogan, Craig J.↗
NASA NTRS1989

Cosmology and the Cosmic Background Explorer (COBE)

COBE, planned for launch aboard a Delta rocket, is NASA's first space mission specifically designed to study the diffuse IR and microwave background radiation. COBE has three instruments for performing precision measurements of the spectrum and angular distribution of the 3 K cosmic background radiation and for making an all-sky survey of the diffuse IR emission at wavelengths of 1-300 microns. COBE will carry differential microwave radiameters to search for anisotropies to a sensitivity per 7-deg pixel of 0.15 mK at frequencies of 53 and 90 GHz and of 0.3 mK at 32 GHz.

Boggess, Nancy W.↗
NASA NTRS1989

The area of isodensity contours in cosmological models and galaxy surveys

The contour crossing statistic, defined as the mean number of times per unit length that a straight line drawn through the field crosses a given contour, is applied to model density fields and to smoothed samples of galaxies. Models in which the matter is in a bubble structure, in a filamentary net, or in clusters can be distinguished from Gaussian density distributions. The shape of the contour crossing curve in the initially Gaussian fields considered remains Gaussian after gravitational evolution and biasing, as long as the smoothing length is longer than the mass correlation length. With a smoothing length of 5/h Mpc, models containing cosmic strings are indistinguishable from Gaussian distributions. Cosmic explosion models are significantly non-Gaussian, having a bubbly structure. Samples from the CfA survey and the Haynes and Giovanelli (1986) survey are more strongly non-Gaussian at a smoothing length of 6/h Mpc than any of the models examined. At a smoothing length of 12/h Mpc, the Haynes and Giovanelli sample appears Gaussian.

Ryden, Barbara S.↗
NASA NTRS1990

Cosmological baryon and lepton number in the presence of electroweak fermion-number violation

In the presence of rapid fermion-number violation due to nonperturbative electroweak effects certain relations between the baryon number of the Universe and the lepton numbers of the Universe are predicted. In some cases the electron-neutrino asymmetry is exactly specified in terms of the baryon asymmetry. Without introducing new particles, beyond the usual quarks and leptons, it is necessary that the Universe possess a nonzero value of B - L prior to the epoch of fermion-number violation if baryon and lepton asymmetries are to survive. Contrary to intuition, even though electroweak processes violate B + L, a nonzero value of B + L persists after the epoch of rapid fermion-number violation. If the standard model is extended to include lepton-number violation, for example through Majorana neutrino masses, then electroweak processes will reduce the baryon number to zero even in the presence of an initial B - L unless 20 M(sub L) approximately greater than the square root of (T(sub B - L) m(sub P1)) where M(sub L) sets the scale of lepton number violation and T(sub B - L) is the temperature at which a B - L asymmetry is produced. In many models this implies that neutrinos must be so light that they cannot contribute appreciably to the mass density of the Universe.

Harvey, Jeffrey A.↗
NASA NTRS1989

An estimate of the velocity correlation tensor - Cosmological implications

The peculiar velocity correlation tensor in the cosmic background radiation is estimated using observations of large-scale streaming motions. Two models are considered, which assume gravitational instability and random phase fluctuations: the CDM (cold dark matter) model representing the standard Omega = 1 CDM dominated universe with adiabatic scale invariant initial fluctuations and the Peebles' baryon isocurvature (PBI) model, an Omega = 0.4 baryon dominated universe with initial isocurvature (entropy) fluctuations. In both cases, the assumed Hubble constant is H = 50 km/sec Mpc. Unlike the CDM model, low Omega, baryon dominated PBI scenarios containing entropy perturbations can lead to correlated velocities over scales exceeding 4,000 km/sec. Predictions of both the CDM and PBI models are discussed. The velocity field in the local standard of rest frame determined by the galaxies themselves is also considered.

Groth, Edward J.↗
NASA NTRS1990

The stability of a collisionless cosmological shell

The P3 M technique is used here to simulate the evolution of collisionless shells in an Omega = 1 universe. Starting from the spherical similarity solution, a bootstrap technique is used to follow the evolution over very large expansion factors. It is found that the overall structure follows the similarity solution for a long period during which bound clumps grow within the shell. At late times the growth of structure depends on induced velocity perturbations in material outside the shell. If such perturbations are suppressed, structure on the shell becomes self-similar. When induced motions in the background medium are included, the evolution at late times is dominated by large-scale modes as predicted by linear stability analysis. The stable final state appears to consist of one or two massive clumps on the edge of a spherical void. The possible application of these results to the origin of galaxies and large-scale structure is discussed.

White, Simon D. M.↗
NASA NTRS1990

The Extended Medium Sensitivity Survey distant cluster sample - X-ray cosmological evolution

The X-ray luminosity function of clusters of galaxies is determined at different cosmic epochs using data from the Einstein Observatory Extended Medium Sensitivity Survey. The sample consists of 67 X-ray-selected clusters that have been grouped in three redshift shells. Evolution is detected in the X-ray properties of clusters. The present volume density of high-luminosity clusters is found to be greater than it was in the past. Given the still limited data set, this result should be regarded as preliminary. It can be interpreted as the consequence of either luminosity evolution or modest density evolution.

Gioia, I. M.↗
NASA NTRS1990

The cosmological evolution models of active galaxies and the extragalactic gamma-ray background

The source spectra and angular fluctuations produced by various possible models of AGN evolution derived from observations in other wavelength bands are investigated. It is found that the sizes of the angular fluctuations are roughly constant between 10 and 100 MeV, independent of the models chosen. None of the models produce the spectral 'shelf' observed at a few MeV, and from the simulation, the AGN mechanism is only a minor contributor to the extragalactic gamma-ray background (EGB), with its flux only about 10 percent of what is observed. These evolution-independent effects imply that the EGB is not solely produced by the AGN mechanism.

Gao, Yi-Tian↗
NASA NTRS1990

Large-scale anisotropy in the extragalactic gamma-ray background as a probe for cosmological antimatter

Intrinsic anisotropies in the extragalactic gamma-ray background (EGB), which should be detectable with the forthcoming Gamma Ray Observatory, can be used to examine some of the mechanisms proposed to explain its origin, one of which, the baryon-symmetric big bang (BSBB) model, is investigated here. In this simulation, large domains containing matter and antimatter galaxies produce gamma rays by annihilation at the domain boundaries. This mechanism can produce mountain-chain-shaped angular fluctuations in the EGB flux.

Gao, Yi-Tian↗
NASA NTRS1990

Ultraviolet spectroscopy of planetary nebulae: Cosmological implications

Optical spectrophotometry of PW Vulpeculae (Nova Vul 1984 no. 1) is combined with ultraviolet data to estimate electron temperatures, densities, and abundances in the ejecta of this slow classical nova. The reddening, distance, and evolution of the ultraviolet spectrum are also discussed. Abundances are nearly solar, with the exception of Nitrogen, which is substantially higher. Although Neon has been reported to be enhanced in several novae, it does not seem to be the case for PW Vul. Photoionization model calculations are presented of the ejecta that give a reasonable match of the observed emission spectrum. A strong featureless continuum shows that very hot, presumably shock heated, gas plays a major role in determining the energetics of this nova. Emission from this hot gas is responsible for the ionization of the nebular gas. A calculation of the masses of both the hot coronal gas and the cooler nebular gas shows that the former may account for most of the mass of the ejecta.

Ferland, Gary J.↗