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NASA NTRS1988

Probes of large-scale structure in the universe

A general formalism is developed which shows that the gravitational instability theory for the origin of the large-scale structure of the universe is now capable of critically confronting observational results on cosmic background radiation angular anisotropies, large-scale bulk motions, and large-scale clumpiness in the galaxy counts. The results indicate that presently advocated cosmological models will have considerable difficulty in simultaneously explaining the observational results.

Suto, Yasushi↗
NASA NTRS1988

A particle astrophysics magnet facility: ASTROMAG

The primary scientific objectives of ASTROMAG are to: examine cosmological models by searching for antimatter and dark matter candidates; study the origin and evolution of matter in the galaxy by direct sampling of galactic matter; and study the origin and acceleration of the relativistic particle plasma in the galaxy and its effects on the dynamics and evolution of the galaxy. These general scientific objectives will be met by ASTROMAG with particle detection instruments designed to make the following observations: search, for anti-nuclei of helium and heavier element; measure the spectra of anti-protons and positrons; measure the isotopic composition of cosmic ray nuclei at energies of several GeV/amu; and measure the energy spectra of cosmic ray nuclei to very high energies.

Ormes, Jonathan F.↗
NASA NTRS1989

Gravitational instability in a primordial collapsing gas cloud

This paper presents an analysis of the linear evolution of short-wavelength perturbations in a background fluid flow which is undergoing gravitational collapse on large scales. Local evolution equations for perturbations to an arbitrary flow are derived in the linear regime and the short-wavelength limit. Local perturbation behavior in an inhomogeneous flow is found to be the same as that in a homogeneous anisotropic flow having the same local velocity field. Background flows in which the scale factors vary as power laws in time are considered to illustrate the relative effects of self-gravity, pressure and kinematics of the background flow on the density perturbation evolution. Perturbation analyses are then presented for more realistic background flows arising from the evolution into the nonlinear regime of initially small density perturbations in an isotropically expanding cosmological model. For low-pressure, inhomogeneous collapses, kinematic effects tend to dominate over self-gravity in driving perturbation growth as the collapse proceeds.

Lacey, Cedric G.↗
NASA NTRS1989

Astromag - Particle astrophysics magnet facility for Space Station Freedom

The Astromag (for astrophysics magnet) superconducting magnet facility to be flown aboard the Space Station in the late 1990s is described together with its scientific objectives. The Astromag facility is basically a magnetic spectrometer capable of determining the momentum per unit charge and the sign of the charge of fully ionized cosmic rays. The Astromag's science goals include investigating the origin and the evolution of matter in the Galaxy by direct sampling of Galactic material, examining cosmological models by searching for antimatter and an evidence of dark matter, and studying the origin of extremely energetic particles and their effects on the dynamics and evolution of the Galaxy. The Astromag's instrumentation will include an array of particle detectors (the WIZard instrument), a large spectrometer (LISA), and a stack of passive high-resolution track detectors in the Astromag's magnetic field (the SCIN/MAGIC instrument).

Jones, W. Vernon↗
NASA NTRS1989

Dark matter candidates

The types of particles which may provide the nonluminous mass required by big-bang cosmological models are listed and briefly characterized. The observational evidence for the existence of dark matter (outweighing the luminous component by at least a factor of 10) is reviewed; the theoretical arguments favoring mainly nonbaryonic dark matter are summarized; and particular attention is given to weakly interacting massive particles (WIMPs) remaining as relics from the early universe. The WIMPs are classified as thermal relics (heavy stable neutrinos and lighter neutralinos), asymmetric relics (including baryons), nonthermal relics (superheavy magnetic monopoles, axions, and soliton stars), and truly exotic relics (relativistic debris or vacuum energy). Explanations for the current apparent baryon/exotica ratio of about 0.1 in different theoretical scenarios are considered, and the problems of experimental and/or observational dark-matter detection are examined.

Turner, Michael S.↗
NASA NTRS1990

The redshift peak at z = 0.06

A catalog of galaxies whose optical spectra contain strong broad emission lines and continua, probably of nonthermal origin, has been completed. The catalog contains about 900 objects, about 700 of which have z of 0.2 or less. A histogram of the redshift distribution for all of the objects in the redshift range 0.02-0.2 and with a large peak at z = 0.06 is shown. Possible interpretations of the peak, which was first seen in 1968, are considered. It is concluded that the only way to explain the peak (and others like it that make up a series of peaks) and still maintain the cosmological redshift hypothesis is to go to cosmological models in which the universe has a multiply connected topology.

Burbidge, G.↗
NASA NTRS1990

Gravitational lensing limits on the cosmological constant in a flat universe

Inflationary cosmological theories predict, and some more general aesthetic criteria suggest, that the large-scale spatial curvature of the universe k should be accurately zero (i.e., flat), a condition which is satisfied when the universe's present mean density and the value of the cosmological constant Lambda have certain pairs of values. Available data on the frequency of multiple image-lensing of high-redshift quasars by galaxies suggest that the cosmological constant cannot make a dominant contribution to producing a flat universe. In particular, if the mean density of the universe is as small as the baryon density inferred from standard cosmic nucleosynthesis calculations or as determined from typical dynamical studies of galaxies and galaxy clusters, then a value of Lambda large enough to produce a k = 0 universe would result in a substantially higher frequency of multiple-image lensing of quasars than has been observed so far. Shortcomings of the available lens data and uncertainties concerning galaxy properties allow some possibility of escaping this conclusion, but systematic searches for a gravitational lenses and continuing investigations of galaxy mass distributions should soon provide decisive information. It is also noted that nonzero-curvature cosmological models can account for the observed frequency of galaxy-quasar lens systems and for a variety of other constraints.

Turner, Edwin L.↗
NASA NTRS1991

Basic physics and cosmology from pulsar timing data

Radio pulsars provide unparalleled opportunities for making measurements of astrophysically interesting phenomena. The author concentrates on two particular applications of high precision timing observations of pulsars: tests of relativistic gravitation theory using the binary pulsar 1913+16, and tests of cosmological models using timing data from millisecond pulsars. New upper limits are presented for the energy density of a cosmic background of low frequency gravitational radiation.

Taylor, J. H.↗
NASA NTRS1992

The density evolution of IRAS galaxies

A maximum likelihood test for density evolution is applied to a full-sky redshift survey of 5297 galaxies selected from the IRAS data base and flux-limited at 1.2 Jy. No evidence for evolution is found. Attention is given to important systematic errors which decrease the certainty with which evolution can be measured, namely, limited knowledge of the cosmological model, the unknown intrinsic spectral energy distribution of IRAS galaxies from 16 to 140 microns, the effect of density fluctuations, a Malmquist-like bias arising from flux errors in the IRAS Point Source Catalog, and possible incompleteness of the sample at high redshifts and low Galactic latitudes. It is shown that the Malmquist bias could result in a significant overestimation of the evolution rate, especially if the catalog has a flux limit near the completion limit of the Point Source Catalog.

Fisher, Karl B.↗
NASA NTRS1992

Gravitational lensing of quasars as seen by the Hubble Space Telescope Snapshot Survey

Results from the ongoing HST Snapshot Survey are presented, with emphasis on 152 high-luminosity, z greater than 1 quasars. One quasar among those observed, 1208 + 1011, is a candidate lens system with subarcsecond image separation. Six other quasars have point sources within 6 arcsec. Ground-based observations of five of these cases show that the companion point sources are foreground Galactic stars. The predicted lensing frequency of the sample is calculated for a variety of cosmological models. The effect of uncertainties in some of the observational parameters upon the predictions is discussed. No correlation of the drift rate with time, right ascension, declination, or point error is found.

Maoz, D.↗
NASA NTRS1991

Gravitational lens determinations of cosmological parameters

Currently available attempts to determine the three classical cosmological parameters (H(0), Omega(0), and Lambda), using gravitational lens techniques and arguments are reviewed. These suggest that H(0) greater than about 75 km/s/Mpc, that contributions to Omega(0) by certain hypothetical types of dark matter are less than 1, and that Lambda is considerably smaller than 3H(0)-squared if a flat cosmological model is assumed. Unfortunately, none of these three conclusions is satisfactorily free of model dependence, possible systematic error, and caveats.

Turner, Edwin L.↗
NASA NTRS1991

The new discussion of a neutrino mass and issues in the formation of large-scale structure

It is argued that the discrepancy between the large-scale structure predicted by cosmological models with neutrino mass (hot dark matter) do not differ drastically from the observed structure. Evidence from the correlation amplitude, nonlinearity and the onset of galaxy formation, large-scale streaming velocities, and the topology of large-scale structure is considered. Hot dark matter models seem to be as accurate predictors of the large-scale structure as are cold dark matter models.

Melott, Adrian L.↗
NASA NTRS1993

Methodological problems with gamma-ray burst hardness/intensity correlations

The hardness and intensity are easily measured quantities for all gamma-ray bursts (GRBs), and so, many past and current studies have sought correlations between them. This Letter presents many serious methodological problems with the practical definitions for both hardness and intensity. These difficulties are such that significant correlations can be easily introduced as artifacts of the reduction procedure. In particular, cosmological models of GRBs cannot be tested with hardness/intensity correlations with current instrumentation and the time evolution of the hardness in a given burst may be correlated with intensity for reasons that are unrelated to intrinsic change in the spectral shape.

Schaefer, Bradley E.↗
NASA NTRS1993

Gamma-ray bursts from stellar mass accretion disks around black holes

A cosmological model for gamma-ray bursts is explored in which the radiation is produced as a broadly beamed pair fireball along the rotation axis of an accreting black hole. The black hole may be a consequence of neutron star merger or neutron star-black hole merger, but for long complex bursts, it is more likely to come from the collapse of a single Wolf-Rayet star endowed with rotation ('failed' Type Ib supernova). The disk is geometrically thick and typically has a mass inside 100 km of several tenths of a solar mass. In the failed supernova case, the disk is fed for a longer period of time by the collapsing star. At its inner edge the disk is thick to its own neutrino emission and evolves on a viscous time scale of several seconds. In a region roughly 30 km across, interior to the accretion disk and along its axis of rotation, a pair fireball is generated by neutrino annihilation and electron-neutrino scattering which deposit approximately 10 exp 50 ergs/s.

Woosley, S. E.↗
NASA NTRS1993

The mass function of clusters of galaxies

The mass function of clusters of galaxies is derived separately from optical and X-ray observations of their respective properties. The mass function was extended to the faint end, to lower masses than the rich clusters, using small groups of galaxies. The derived mass function is within the mass range from approximately 10 exp 12 to not less than 10 exp 15/h solar masses. The deduced density range n is approximately 10 exp -2 to 10 exp -8 cubic h/cubic Mpc. The observed shape of the mass function exhibits a shallow power-law decrease with mass at the faint end, and a steep exponential decrease with mass at the massive end. A summary of some constraints placed by the observed mass function on current cosmological models is presented.

Bahcall, Neta A.↗
NASA NTRS1993

BATSE observations of gamma-ray burst spectra. I - Spectral diversity

We studied the time-averaged gamma-ray burst spectra accumulated by the spectroscopy detectors of the Burst and Transient Source Experiment. The spectra are described well at low energy by a power-law continuum with an exponential cutoff and by a steeper power law at high energy. However, the spectral parameters vary from burst to burst with no universal values. The break in the spectrum ranges from below 100 keV to more than 1 MeV, but peaks below 200 keV with only a small fraction of the spectra breaking above 400 keV; it is therefore unlikely that a majority of the burst spectra are shaped directly by pair processes, unless bursts originate from a broad redshift range. The correlations among burst parameters do not fulfill the predictions of the cosmological models of burst origin. No correlations with burst morphology or the spatial distribution were found. We demonstrate the importance of using a complete spectral description even if a partial description (e.g., a model without a high-energy tail) is statistically satisfactory.

Band, D.↗
NASA NTRS1992

Gamma ray bursts from collisions of primordial small mass black holes with comets

Recent results of BATSE (a collaborative project on independent sky surveys of gamm ray bursts and optical sky patrols) reinforce the isotropic distribution of gamm-ray bursts. Alternatively to cosmological models, collisions between small mas primordial black holes and comets in the Oort cloud are proposed. Assuming typical Oort cloud densities and velocities for comets and primordial black holes, many of the observed properties of gamma-ray bursts can be explained.

Bickert, K. F.↗