Showing papers on "Deceleration parameter published in 1976"

Dynamical friction: the Hubble diagram as a cosmological test.

Abstract: Effects on the Hubble diagram of the frictional accretion of small cluster galaxies by large ones, to which Ostriker and Tremaine have recently drawn attention, must be accurately determined if the magnitude-redshift relation is to become a viable cosmological test. We find that the process might be detectable through the concomitant change in galaxy colors, but that its effect on the dispersion of magnitudes of first-ranked cluster galaxies would be negligible even if the change in average magnitude is very important. The sign of the effect of accretion on the luminosity observed within a given aperture depends on the structures of the galaxies involved. The size of the effect not only depends sensitively on the galaxy structures, but is also amplified when the relatively recent collapse times of the clusters are taken into account. It is vital to answer the complicated observational and theoretical questions raised by these preliminary calculations, because the Hubble diagram remains the most promising approach to the deceleration parameter q/sub 0/. Local tests of the density of the universe do not give equivalent information. (AIP)

The dynamics of the intergalactic medium in the vicinity of clusters of galaxies

Abstract: Numerical solutions to the problem of infall of matter into clusters of galaxies are presented. It is assumed that the universe can be described by a Friedmann cosmological model with a Hubble constant 50 km/s/Mpc. It is found that physically reasonable models having a deceleration parameter of 1/2 lead to excessive X-ray emission from clusters of galaxies. Models including a heat flux due to thermal conduction, heating of the intracluster medium by galaxy motions, and a gas outflow from the galaxies in the cluster are discussed, and the results are compared with the observational data in both the X-ray and radio bands. It is concluded that the density parameter must be less than 0.2 in order that the predicted X-ray emission not exceed that observed. No models have been found which give a good description of the observed cluster X-ray sources, with the exception of a fully adiabatic model in a high-density universe.

The effect of intergalactic dust on the measurement of the cosmological deceleration parameter q 0

Abstract: In a recent attempt to explain the cosmic microwave background without the big bang, a thermalization mechanism involving intergalactic whisker grains of graphite was proposed. The effect of absorption by the intergalactic medium in general, and of the above type in particular, on the measurement of the deceleration parameterq 0 of the expanding universe is discussed. Its effect is shown to be comparable in magnitude but opposite to that of the luminosity evolution in galaxies. A consequential selection effect is also discussed.

Some astrophysical effects of the time variation of all masses.

Abstract: The possibility that all rest-masses change with time was recently raised as a result of group-theoretical analysis of masses and spins in curved spacetime. In the present paper astrophysical and cosmological results of such a mass variation are derived and compared with the results of (a) Dirac's old theory of varying gravitation constant G;(b) Dirac's new theories with additive and multiplicative creation of matter; (c) the Hoyle-Narlikar theory. For all these theories we obtain an approximate correction to the cosmological deceleration parameter q/sub 0/ by estimating the evolution of giant elliptical galaxies when the masses of all particles or G vary with time. We then show that of the three cosmologies of Dirac, all but the one with multiplicative creation of matter lead to evolutionary corrections which result in a large negative value of the corrected q/sub 0/, independent of model parameters. This is in contradiction to the predicted value of q/sub 0/ for these cosmologies and the observations of q/sub 0/ even when a large allowance is made for uncertainties. The same conflict is shown to occur in the Hoyle-narlikar cosmology. When the masses of all particles vary according to the group-theoretical analysis, we find that no such conflictmore » arises; and for reasonable model parameters and the present measurements of q/sub 0/, the corrected q/sub 0/>0 as required by the theory. The mass-changing cosmology is also shown to be compatible with the evidence for the big bang. We then show that this same mass-variation gives rise to a slow increase in the average blackbody temperature of the Earth when all atmospheric effects are neglected. Finally, we discuss relevant observational tests of the mass-varying cosmology: in particular, Shapiro's radar ranging experiments. (AIP)« less