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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1979

Cosmology of a charged universe

The Proca generalization of electrodynamics admits the possibility that the universe could possess a net electric charge uniformly distributed throughout space, while possessing no electric field. A general-relativistic model of cosmological expansion dominated by such a charged background has been calculated, and is consistent with present observational limits on the Hubble constant, the deceleration parameter, and the age of the universe. However, if this cosmology applied at the present epoch, the very early expansion of the universe would have been too rapid for cosmological nucleosynthesis or thermalization of the background radiation to have occurred. Hence, domination of the present expansion by background charge appears to be incompatible with the 3-K background and big-bang production of light elements. If the present background charge density were sufficiently small (but not strictly zero), expansion from the epoch of nucleosynthesis would proceed according to the conventional scenario, but the energy due to the background charge would have dominated at some earlier epoch. This last possibility leads to equality of pressure and energy density in the primordial universe.

Barnes, A.↗
NASA NTRS1979

A limit to the X-ray luminosity of nearby normal galaxies

The hypothesis that normal galaxies are on the average more luminous in the X-ray region than the Milky Way galaxy or M31 and therefore are possible candidates for the low-luminosity sources of the 2 to 60 keV extragalactic diffuse background is tested. Data from the A-2 detectors on the HEAO-1 spacecraft were examined for emission from positions coincident with 76 selected normal galaxies, and upper limits to the average galactic luminosity for various luminosity distributions resulting in the observed count rate distribution were determined. For uniform and exponential galactic luminosity distributions, limits of 2.7 x 10 to the 38th erg/sec and 3.4 x 10 to the 38th erg/sec, respectively, at the 90% confidence level were obtained. It is shown that the Hubble-constant-independent upper limit to galactic emissivity is less than 1% of the diffuse background emissivity, indicating that normal galaxies are not responsible for the diffuse X-ray background and have luminosities comparable to that of the Galaxy.

Worrall, D. M.↗
NASA NTRS1980

QSO evolution and the intergalactic medium

A model is developed of a cold, photoionized intergalactic medium in which only discrete, evolving sources (quasars) produce the observed extragalactic hard X-ray background. Constraints on the model are imposed by observed optical depth limits to various redshifts, far UV and visible flux measurements, X-ray background and source counts in the region 2-6 keV, and it makes use of results of the Palomar Bright Quasar Survey and the Braccesi Quasar survey to obtain expressions for the quasar evolution function, absolute luminosity, present number density and switch-on redshift. Results of computer modeling reveal an intergalactic medium with a density with respect to closure less than 0.35, temperature of 16,000 K and fractional ion abundances of approximately 0.000001 for H I and 0.001 for He II, under the assumption of a Hubble constant of 50 km/sec per Mpc. In addition, spectral indices of -0.4 and -1.3 are obtained for the regions of the emission spectrum above and below 4 x 10 to the 18th Hz.

Sherman, R. D.↗
NASA NTRS1980

B2 1141 + 37 - A giant radio galaxy with remarkable radio and optical properties

Observations of the giant radio galaxy B2 1141+37, which has a widely separated two-component radio structure and is optically identified with a tight chain of galaxies, are reported. The source was observed at 4900 MHz with the VLA at an effective integration time of 17 min. The map obtained shows two radio lobes with maxima coinciding with those in a previous 1415 MHz map and intensities about 1.5 times smaller than those obtained by extrapolating the spectrum defined by the flux density at 408 and 1415 MHz. Measurements of the redshifts of the two brightest galaxies identified with the radio source with an image intensified dissector scanner result in values of 0.1145 and 0.1155, which imply, with a Hubble constant of 50 km/sec per Mpc, a distance of 687 Mpc to the radio source and a separation of 1.0 Mpc between the lobes making it one of the largest radio sources known.

Ulrich, M. H.↗
NASA NTRS1981

Q0957+561 - Detailed models of the gravitational lens effect

The galaxy responsible for causing multiple gravitational lens images of QSO Q0957+561 has been reobserved spectroscopically and a more accurate redshift of 0.36 was obtained. In addition, detailed models of the gravitational lens effect were computed. These models, which can explain all optical and radio data for the system, predict delays of up to five years between variations in the A and B images (with A preceding B). It is suggested that the third image is rather faint and located close to the center of the lens galaxy; it is possible that this third image contributes to the observed galaxy core. The possibility that this system can be used to measure the Hubble constant is discussed.

Young, P.↗
NASA NTRS1982

Evidence for 200 second variability in the X-ray flux of the quasar 1525 + 227

Sixteen hundred seconds of Einstein Observatory IPC data for 1525 + 227, a bright, nearby quasar show significant intensity fluctuations on a time scale of 200 seconds. Similar fluctuations were not detected 13 months later during a follow-up 12,500 second observation. Interpretation of the time variations requires a Hubble constant equal to or greater than 100 km/s per Mpc to obtain even marginal consistency with standard isotropic emission models. An alternative interpretation invokes anisotropic emission probably due to the presence of relativistic motions with associated beaming effects.

Matilsky, T.↗
NASA NTRS1983

The dynamics of rich clusters of galaxies. II - The Perseus cluster

The dynamics of the Perseus cluster are analyzed using self-consistent equilibrium analytical models. Using existing data in the literature plus new radial velocities reported here, composite surface density and velocity dispersion profiles are derived. These profiles have been compared with dynamical models described by Kent and Gunn (1982). The best fit suggest the presence of a significant degree of anisotropy in the velocity distribution: galaxy orbits are constrained to pass within a radius of seven cluster radii, or 1.3 deg of the cluster center. For Hubble constant = 50, a core radius of 340 kpc 11 arcmin and a mass to visual light ratio M/L = 300 are found. Using these results, X-ray observations of the intracluster medium in Perseus are reanalyzed. A previously noted discrepancy between the observed temperature of the hot gas and the cluster velocity dispersion is reduced but not eliminated. A cooling accretion flow previously deduced to exist in this cluster is shown to extend to only about one-third of the cluster radius.

Kent, S. M.↗
NASA NTRS1983

Astrophysical consequences of a violation of the strong equivalence principle

The consequences of a supposed violation of the strong equivalence principle (SEP) for photons are analyzed theoretically and investigated using published observational data on the age of stars and globular clusters, the past temperature of the earth, the 3-K black-body radiation, and big-bang nucleosynthesis. It is shown that the photon number is unaffected by an SEP violation, which influences only massive particles. The observational data are found to be compatible with an SEP violation of the order of the Hubble constant during the matter-dominated era, while not demanding such a violation. More direct-measurement studies, based on data such as those from the Viking program, are proposed.

Canuto, V. M.↗
NASA NTRS1983

The value of Ho

A brief discussion of the systematic effects of selection bias on the extragalactic distance scale is given. Distance indicators with intrinsic scatter yield only upper limits to Ho, unless the true intrinsic scatter is either small or well determined. Several distance indicators (luminosity index, diameters, globular clusters, 21 cm line widths) are discussed. It is concluded that type I supernovae, calibrated through brightest M supergiants, yield presently the most reliable determination of the large-scale value of the Hubble constant, i.e., 50 + or - 7 km/s Mpc.

Tammann, G. A.↗
NASA NTRS1983

The Einstein observatory medium sensitivity survey - The quasars sample

A complete sample of X-ray-selected quasars and Seyfert galaxies extracted from the Einstein Observatory Medium Sensitivity Survey is described, and their physical characteristics are discussed. A Hubble constant of 50 km/s per Mpc and a Friedmann universe with a deceleration parameter of q(0)=0 are assumed throughout the survey, and the sample of X-ray sources was selected according to the following criteria: the significance of the detection exceeds a confidence level of 5 beta; the source is physically unrelated to the target of the IPC observation; and that the source is at a galactic latitude higher than 20 deg. The redshift and optical luminosity distributions of 55 Active Galactic Nuclei (AGNs) detected in the survey are discussed. A number flux relation for the different classes of extragalactic objects are analyzed in detail, using a Maximum Likelihood method and the assumption that the relation can be represented as a power law.

Gioia, I. M.↗
NASA NTRS1986

Spectral flux from low-density photospheres - Numerical results

Radiative transfer through sharp, quasi-static atmospheres whose opacity is dominated by hydrogen is considered at densities low enough that scattering usually dominates absorption and radiative excitations usually dominate collisional excitations. Numerical results for the continuum spectral flux are obtained for effective temperatures T(e) = 6000-16,000 K and scale heights Delta-R = 10 to the 10th - 10 to the 14th cm. Spectra are significantly different than if LTE level populations were assumed. Comparison with observations of the Type II supernova 1980k tends to increase the value of the Hubble constant previously obtained by the Baade (1926) method.

Hershkowitz, S.↗
NASA NTRS1986

Spectral flux from low-density photospheres - Approximate results

Radiative transfer through sharp, quasi-static atmospheres containing mostly hydrogen is considered at densities low enough that scattering dominates absorption and collisional excitations are negligible. It is found that the balance between photoionization and radiative recombination which governs the atomic level populations greatly reduces the effective absorptive opacity. Approximate results for the emergent continuum spectral flux are obtained, significantly different than if local thermodynamic equilibrium level populations were assumed. The flux jumps at the photoionization thresholds are relatively small for the photospheric temperatures T sub p(v) greater than or about 6000 K considered, and T sub p increases toward the far-ultraviolet. It appears that the lack of a Balmer jump in spectra of Type II supernovae implies that the flux is diluted below that of a blackbody at the same color temperature, which increases the value of the Hubble constant obtained by the Baade (1926) method.

Hershkowitz, S.↗
NASA NTRS1985

The Virgo cluster redshift survey

A complete (99 percent) velocity survey is presented of the 471 galaxies brighter than m(pg) = 15.5 that are within the 6-deg radius of the central region of the Virgo cluster. There are 602 galaxies with measured velocities in the 6-deg circle, of which about 362 have the velocities lower than 3000 km/s and are assumed to be cluster members. From the velocity data, the cluster luminosity function was derived, and the mean Virgo velocity (for the Hubble constant and Virgo infall calculations) was calculated. In addition, the velocity data were used to study internal dynamics of the Virgo cluster.

Huchra, J. P.↗
NASA NTRS1986

On the determination of cosmological parameters

The current state of the observational determination of the Hubble constant, deceleration parameter, and the mean mass density is briefly reviewed. The methods of arriving at current values for these numbers are summarized. Prospects for further advances in these determinations are assessed.

Huchra, John P.↗
NASA NTRS1988

Lower bound on e+e- decay of massive neutrinos

Astronomical observations of SN1987A, such as the light curve, spectral intensities of lines, the X-ray emissions, etc., constrain the lifetime for the decay of a heavy neutrino 1 MeV less than or equivalent to m sub nu H less than or equal to 50 MeV through nu sub H yields nu sub 1+e(+)+e(-) exceeds 4 x 10 to the 15th exp(-m sub nuH/5MeV) seconds. Otherwise. resulting ionization energy deposits and stronger X-ray emission would have been observed. This coupled with traditional cosmological considerations argues that the lifetime of tau-neutrinos probably exceeds the age of the universe. This in turn would imply the standard cosmological mass bound does apply to nu sub tau, namely m sub nu sub tau less than or equivalent to 100 h squared eV (where h is the Hubble constant in units of 100 km/sec/mpc). The only significant loophole for these latter arguments would be if nu sub tau primarily decays rapidly into particles having very weak interactions.

Cowsik, R.↗
NASA NTRS1988

Analysis of spatially resolved IUE spectra of 0957+561A,B: A gravitationally lensed double quasar

A study of 18 IUE spectra of the gravitationally lensed quasar, 0957+561A,B was used to search for time delays between light variation in the 2 components. Evidence for substantial, rapid variability in Component A in 1980, followed by a light variation in the other component 20 months later is found. However, it is argued that these variations do not record the same event in the quasar, and so, cannot be used to derive a value for the Hubble constant. The cause of the rapid variation in Component A in 1980 is not understood, but it does not appear to be a microlensing event.

Altner, Bruce↗
NASA NTRS1988

The distribution of dark matter, galaxies, and the intergalactic medium in a cold dark matter dominated universe

The evolution and distribution of galaxies and the intergalactic medium (IGM) have been studied, along with collisionless dark matter in a Universe dominated by cold dark matter. The Einstein-deSitter universe with omega sub 0 = 1 and h = 0.5 was considered (here h = H sub 0 bar 100/kms/Mpc and H sub 0 is the present value of the Hubble constant). It is assumed that initially dark matter composes 90 pct and baryonic matter composes 10 pct of total mass, and that the primordial baryonic matter is comprised of H and He, with the abundance of He equal to 10 pct of H by number. Galaxies are allowed to form out of the IGM, if the total density and baryonic density satisfy an overdensity criterion. Subsequently, the newly formed galaxies release 10 to the 60th ergs of energy into the IGM over a period of 10 to the 8th years. Calculations have been performed with 32 to the 3rd dark matter particles and 32 to the 3rd cells in a cube with comoving side length L = 9.6/h Mpc. Dark matter particles and galaxies have been followed with an N-body code, while the IGM has been followed with a fluid code.

Ryu, Dongsu↗
NASA NTRS1989

Primordial lithium and the standard model(s)

The results of new theoretical work on surface Li-7 and Li-6 evolution in the oldest halo stars are presented, along with a new and refined analysis of the predicted primordial Li abundance resulting from big-bang nucleosynthesis. This makes it possible to determine the constraints which can be imposed on cosmology using primordial Li and both standard big-bang and stellar-evolution models. This leads to limits on the baryon density today of 0.0044-0.025 (where the Hubble constant is 100h km/sec Mpc) and imposes limitations on alternative nucleosynthesis scenarios.

Deliyannis, Constantine P.↗