Showing papers on "Hubble's law published in 1986"

Determining the Hubble constant from gravitational wave observations

Abstract: I report here how gravitational wave observations can be used to determine the Hubble constant, H0. The nearly monochromatic gravitational waves emitted by the decaying orbit of an ultra–compact, two–neutron–star binary system just before the stars coalesce are very likely to be detected by the kilometre–sized interferometric gravitational wave antennas now being designed1–4. The signal is easily identified and contains enough information to determine the absolute distance to the binary, independently of any assumptions about the masses of the stars. Ten events out to 100 Mpc may suffice to measure the Hubble constant to 3% accuracy.

Large-scale velocity fields as a test of cosmological models

Abstract: It has been suggested1,4,5–7 that the Hubble expansion on large scales (∼50h−1 Mpc, where h is the Hubble constant in units of 100 km s−1 Mpc−1) is distorted by bulk matter flows of surprisingly large amplitude Using Bayesian statistics of conditional probability, we show here that a high amplitude for large-scale matter flows can be used to rule out, at the 95% confidence level or better, both hot dark matter and cold dark matter models of the growth of structure in the Universe No random-phase initial conditions with constant-curvature initial perturbations are likely to be consistent with bulk flows relative to the cosmic microwave background (CMB) exceeding 700 km s−1 on scales of 50h−1 Mpc If the Universe is dominated by cold dark matter and galaxies are a biased mass tracer, then the bulk velocity on this scale should not exceed 150 km s−1

Evidence for a nonvanishing energy density of the vacuum (or cosmological constant)

Abstract: The better understanding of the synthesis of heavy elements by the r-process-based on an improved description of nuclear beta decay far from stability -, and the investigation of globular clusters led to a larger age of the universe of ≥ 15 × 109 a. It will be shown that with the assumption of inflationary expansion at the beginning of the evolution of the universe such a number leads to a nonvanishing cosmological constant A in the Friedmann equation for a Hubble constant H0 ≥ 45 Mpc-1 sec-1. Consequences of a nonvanishing A (corresponding to a nonvanishing energy density of the vacuum) are more stringent limits on the amount of dark matter in the universe and on the neutrino mass.

Simple model for the inflationary expansion of the early Universe.

Abstract: The evolution of the early Universe is studied under the following assumptions. (1) The large-scale structure of the Universe is homogeneous and isotropic and governed by the Robertson-Walker metric in flat space with a spatial scale factor a(t). (ii) Matter can be described by a quantum-mechanical N-vector model with a single- or double-well potential. (iii) The system is initially in thermal equilibrium at some high temperature T relative to the Planck temperature. Quantitative progress is possible in the large-N limit where the phase structure of the N-vector model is known exactly. The evolution of the system is characterized by three time regimes. For the earliest times the main effect of gravity is to rapidly decrease the kinetic energy of the system, while the potential energy and the local ''order''-parameter fluctuation S(t) change very little. Thus the system is driven far from equilibrium. There is rapid growth of a(t) during this period. One enters the intermediate time period after a(t) is sufficiently large that the spectrum of the order-parameter correlation function ''freezes'' due to red-shifting. By this time the energy density epsilon is dominated by the potential energy and one enters a de Sitter phase where, approximately, the pressure P =more » -epsilon and a(t) is growing exponentially. In this regime the Hubble constant and S(t) are decaying exponentially with precisely the same slow rate. The amount of inflation depends most strongly on the initial temperature (lnaapprox. =(T/T/sub P/)/sup 2/) where T/sub P/ is the Planck temperature.« less

The Hubble Ratio from Sosies of M31 in the Virgo S Cloud and in the Hercules Supercluster

Abstract: L'etude par la methode des galaxies sosies conduit a un rapport de Hubble H*=99±15 kms −1 Mpc −1 . La constante de Hubble peut en differer de quelques pourcent selon le modele cosmologique

On the distance measure for gravitational lenses

Abstract: A discussion is presented of some of the physical elements that are important for geometric optics in curved space-time, with a view toward interpreting data on gravitational lenses. This is important because each gravitational lens provides geometrical information about an arc that crosses a substantial portion of the universe. The propagation of photons along long arcs is highly sensitive to the mean density in the beam, averaged along the arc. Fluctuations about this mean are not important unless their scale is comparable to that of the universe. Tidal distortion is important if only a few lumps are involved. The variation in the geometrical optics is considerably greater if there is a nonzero cosmological constant.

Perturbation of the nearby extragalactic velocity field by the Local Group

Abstract: Etude de la relation vitesse-distance dans le champ galactique tres proche, a partir d'un echantillon de 48 galaxies. L'influence de la deceleration due a la masse du Groupe Local est faible; elle est negligeable au-dela de 25-3 Mpc

Directly observed relations in complete galaxy samples and the predictions of redshift-distance power laws.

Abstract: Directly observed relations in complete galaxy samples (apparent magnitude or diameter vs. redshift) are compared with the predictions of redshift-distance power laws. The predictions are obtained by an objective, nonparametric, statistically uniform, and fully reproducible procedure. In all cases the linear law fits even more poorly than a cubic law, and the optimal law is approximately quadratic. Even a 1.2 power law is conspicuously better-fitting than a linear law. The results of the present study in terms of directly measured quantities are consistent with and confirm earlier studies in terms of theoretical quantities such as absolute magnitudes and diameters. They show that there is no positive evidence for the Hubble law in manifestly fair galaxy samples and that the law can be reconciled with the data in complete samples only, if at all, by the adjunction of a tissue of ancillary hypotheses, none of which is capable of direct observational substantiation.

Primordial density fluctuations

Abstract: For potentials with an almost flat section the authors derive a general expression for the time evolution of energy density correlations inside the horizon, for an arbitrary quantum state. The particular case of the de Sitter invariant vacuum is studied in detail. At the horizon they find an energy contrast being one order of magnitude larger than usual estimates based on the Hawking temperature. The source for this contribution are quantum fluctuations at short distances. The authors also estimate the small corrector due to the time dependence of the Hubble constant.

Measuring the Hubble Constant

Abstract: Hubble's celebrated constant, which relates the recessional velocities of galaxies to their distances, is perhaps the most important number in extragalactic astronomy. Using it, along with their favorite models, astronomers and cosmologists derive the age of the universe, estimate its size, calculate the luminosity of quasars and much more. Unfortunately, astronomers are far from agreeing on a value for Hubble's constant. Some believe that H0 is about 50 km/sec Mpc; others think it is closer to 100 km/sec Mpc. Depending on the details of the cosmological model chosen, this can lead to a discrepancy of a factor of 2—ten billion years or so—in the age of the universe.

Deviation from Hubble flow, biased galaxy formation, and the mass density of the Universe.

Abstract: A wide variety of numerical models of gravitational clustering are used to assess error in estimates of the mass density of the Universe from Virgo infall. The mean estimate of density is too low in both critical-density and low-density models, and it has a large dispersion in all models. Biased cold-dark-matter models produce an estimate of mass density in good agreement with observational estimates from infall.

Constraints on the Age of the Universe from Globular Clusters and the Cosmic Expansion Rate

Abstract: It is appropriate here to note the 60th birthday Allan Sandage has celebrated last month and who — in 1968 — first pointed out in a paper entitled “The Time Scale of Creation” [1] the amazing agreement of three totally independent time scales, i.e. the age of the oldest stars, the age of the radioactive elements, and the expansion age of the universe. During the last almost 20 years these ages have been revised numerically, but the agreement persists.

Evolution of a hot universe with massive unstable leptons

Abstract: The various aspects of the presence of unstable massive neutrinos in the early universe are analyzed in this paper. The thermal history of the universe and the cosmological nucleosynthesis are calculated. Bounds on the mean baryon density in the universe and on the mass and the decay constant of the heavy leptons are obtained. Comparison with the available observations of the abundance of light elements make it possible to show that a model with m H = 5-100 HeV and T H = 103-104 sec agrees satisfactorily with the observations if ~b = 0.030.06 and the Hubble constant is H 0 = 50 km-sec-l.Hpc -I.

Galaxy distances and deviations from universal expansion; Proceedings of the NATO Advanced Research Workshop, Kona, HI, Jan. 13-17, 1986

Abstract: A collection of papers on galaxy distances and deviations from universal expansion is presented. Individual topics addressed include: new results on the distance scale and the Hubble constant, Magellanic Clouds and the distance scale, CCD observations of Cepheids in nearby galaxies, distances using A supergiant stars, infrared calibration of the Cepheid distance scale, two stepping stones to the Hubble constant, physical models of supernovae and the distance scale, 21 cm line widths and distances of spiral galaxies, infrared color-luminosity relations for field galaxies, minimizing the scatter in the Tully-Fisher relation, photometry of galaxies and the local peculiar motion, elliptical galaxies and nonuniformities in the Hubble flow, and large-scale anisotropy in the Hubble flow. Also discussed are: improved distance indicator for elliptical galaxies, anisotropy of galaxies detected by IRAS, the local gravitational field, measurements of the CBR, measure of cosmological times, ages from nuclear cosmochronology, extragalactic gas at high redshift, supercluster infall models, Virgo infall and the mass density of the universe, dynamics of superclusters and Omega(0), distribution of galaxies versus dark matter, peculiar velocities and galaxy formation, cosmological shells and blast waves.

New model of the metagalaxy

Abstract: The known physical laws do not exclude the existence of anticollapsing bodies in nature (anticollapse is a gravitational collapse with time reversal). In the paper it is shown that the metagalaxy, i.e. the observed part of the universe, may in first approximation be the interior of a giant anticollapsing body having a boundary beyond the particle horizon. This is the “anticollapse model” of the metagalaxy. The advantage of this model follows from the fact that some anisotropies in the metagalaxy, e.g. the cosine-anisotropy of the intensity of cosmic background radiation, the cosine-anisotropy of the Hubble parameter at a given distance, the gradient of the mean matter density, etc. are already considered in first approximation. The theoretical considerations about anticollapse show and the present-day cosmological observations support the opinion that the anticollapse model of the metagalaxy is better than the usual Friedmann model.

Cosmological deceleration and peculiar motion

Abstract: Le taux de variation du deplacement vers le rouge d'une source cosmologique isolee peut resulter partiellement du mouvement particulier de la source. On a obtenu une formule donnant ce taux et on l'applique a quelques cas observables

The motion of the sun and the local group and the velocity dispersion of "field" galaxies

Abstract: Distances to a complete sample of nearby galaxies with radial velocities less than 500 km/s computed via the blue Tully-Fisher relation are used to redetermine the vector of the solar motion, the streaming motion of the Local Group of galaxies and the velocity dispersion of field galaxies The Hubble expansion is found only outside the Local Group An upper limit of 120 km/s for the velocity dispersion of “field” galaxies within 10 Mpc is derived

On the determination of cosmological parameters

Abstract: 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.

Calibration of the Infrared Tully-Fisher Relation and the Global Value of the Hubble Constant

Abstract: Among existing secondary distance indicators, the IR Tully-Fisher relation is probably the most reliable available for measuring the far flung Hubble flow. Absolute calibration of the method, however, remains highly uncertain owing to the poor state of nearby galaxy distances. A coordinated ground-based and space attack on this problem, primarily involving Cepheids, holds out great promise for a measurement of the Hubble constant good to ten percent.

Vacuum Energy in Cosmic Dynamics

Abstract: The analysis of the Th/U ratio in meteorites and the evolutionary ages of globular clusters favour values of the cosmic age of (19±5)×109 yr. This evidence together with a Hubble parameterH 0>70 km s−1 Mpc−1=(14×109 yr)−1 cannot be reconciled in a Friedmann model with Λ=0. It requires a cosmological constant in the order of 10−56 cm−2, equivalent to a vacuum densityρ v =10−29 g cm−3 The Friedmann-Lemaitre models (Λ>0) with a hot big-bang have been calculated. They are based on a present value of the baryonic matter density ofρ 0=0.5×10−30 g cm−3 as derived from the primordial4He and2H abundances. For a Hubble parameter ofH 0=75 km s−1 Mpc−1, our analysis favours a set of models which can be represented by a model with Euclidean metric (density parameter Ω0=1.0, deceleration parameterq 0=−0.93, aget 0=19.7×109 yr) and by a closed model with perpetual expansion (Ω0=1.072,q 0=−1.0, aget 0=21.4×109 yr). A present density parameter close to one can indeed be expected if the conjecture of an exponential inflation of the very early universe is correct. The possible behaviour of the vacuum density is demonstrated with the help of Streeruwitz' formula in the context of the closed model with an inflationary phase at very early times.

Evidence for a Nonvanishing Energy Density of the Vacuum or Cosmological Constant

Abstract: The better understanding of the synthesis of heavy elements by the r-process-based on an improved description of nuclear beta decay far from stability -, and the investigation of globular clusters led to a larger age of the universe of ≥ 15 × 109 a. It will be shown that with the assumption of inflationary expansion at the beginning of the evolution of the universe such a number leads to a nonvanishing cosmological constant A in the Friedmann equation for a Hubble constant H0 ≥ 45 Mpc-1 sec-1. Consequences of a nonvanishing A (corresponding to a nonvanishing energy density of the vacuum) are more stringent limits on the amount of dark matter in the universe and on the neutrino mass.

New Results on the Distance Scale and the Hubble Constant

Abstract: The following topics are discussed: galactic extinction, primary distance indicators, distance moduli in the Local and Sculptor groups, luminosity index, HI line width, velocity dispersion, sosies, supernovae, Malmquist bias, distance to the Hercules supercluster and Hubble constant. The best estimate is still 90 ≦ H0 ≦ 100.