Open Universe Models Research Articles

Dust–radiation universes: stability analysis

Flat and open universe models are considered, containing a mixture of cold matter (dust) and radiation interacting only through gravity, with the aim of studying their stability with respect to linear scalar perturbations. To this end the perturbed universe is considered as a dynamical system, described by coupled differential equations for a gauge\hs invariant perturbation variable and a relevant background variable. The phase\hs space analysis of this dynamical system shows that flat dust\hs radiation models are unstable, and open models structurally unstable, with respect to adiabatic perturbations. It is shown that there are perturbations which decay even if their wavelength at equidensity is larger than the corresponding Jeans scale. Metric and curvature perturbations are also briefly discussed. We believe that this analysis gives a clearer idea of the stability properties of realistic universe models than the standard one based on the Jeans scale, despite our simplifying assumptions.

Perturbations of the Cosmic Microwave Background Radiation and Structure Formations

After the recent discovery of temperature fluctuations of the cosmic microwave background radiation by COBS, the study of the temperature fluctuations becomes more and more important for understanding formations of large scale structures of the universe. The treatments for the evolution of small density fluctuations of matters and radiation by gauge invariant formalism are summarized. And the expected values of temperature anisotropies in various cosmological models are shown. Both flat and open universe models with and without the cosmological constant are considered. As for open universe models, in particular, any work had never been done by the complete treatment on large scale anisotropies. However we could find the complete formula to handle large scale temperature anisotropies and here this formula is adopted

Surviving cosmological models after the discovery of large-angle anisotropies of the cosmic microwave background

Using new and first detections of the rms temperature fluctuations at 10° and the quadrupole anisotropy on the cosmic microwave background radiation by the COBE group together with the upper limits on small-scale anisotropies, constraints on various cosmological models are obtained. Complete analysis of the quadrupole anisotropy for flat and open universe models has been done

Constraints on open universe models from quadruple anisotropy of the cosmic microwave background

The quadrupole anisotropy of the cosmic microwave background expected in a variety of open universe models is evaluated by taking full account of contributions from both the generalized Sachs-Wolfe effect and intrinsic photon fluctuations at decoupling. Comparing the results with the observed upper limit of the quadrupole anisotropy, constraints on open universe models are derived. It is concluded that, even if the most conservative attitude is adopted, both hot and cold dark matter models with h = 0.5, Omega(0) not greater than 0.2 and all pure baryonic models with Omega(0) not greater than 0.2 are excluded if the initial density spectrum has the power-law index n not greater than 1, while both hot and cold dark matter models with h = 1.0, Omega(0) not greater than 0.2, and n not greater than 1 are marginally consistent with the observed upper limit of the quadrupole if one allows possible ambiguities in the normalization of the perturbation amplitudes. 29 refs.

Isocurvature baryon-dominated open universe - Structure of galactic halos

Structure of galactic halos in the isocurvature baryon-dominated open universe models is calculated. The halos' rotation curves are calculated analytically, based on the secondary infall paradigm. The nonvanishing curvature of the expanding universe introduces scale dependence of final virial structure of the halos, assuming they are formed dissipationlessly by hierarchical clustering. For primordial scale-free power spectra, with a spectral index in the range of n = 0 to -1, and Omega(0) of about 0.1, the predicted galactic halos rotation curves are found to be steeply decreasing with radius. Given the observed amplitude and extent of the rotation curves of giant spiral galaxies and the nucleosynthesis bounds on the baryon mean density, the allowed range of parameters yields only halos with falling rotation curves, in clear disagreement with the observed flat galactic rotation curves. 33 refs.

Large-scale cosmic microwave background anisotropies in isocurvature baryon open universe models

view Abstract Citations (29) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Large-Scale Cosmic Microwave Background Anisotropies in Isocurvature Baryon Open Universe Models Gorski, Krzysztof M. ; Silk, Joseph Abstract We calculate the large angular scale cosmic microwave background anisotropy in a low-density baryon-dominated universe with isocurvature primordial inhomogeneities. In models in which the initial power spectra of perturbations are steeper than white noise, P(k) is proportional to k^n^, n < 0, predictions for the quadrupole moment of the anisotropy are found to be in conflict with existing observational limits, if the universe remained fully ionized and Compton drag inhibited growth of inhomogeneities until z ~ 100. In order to lower the amplitude of the anisotropy, one has to substantially prolong the duration of the growth phase of density perturbations, while smearing out fine-scale anisotropies, thereby requiring reionization to occur at a redshift smaller than 100, but larger than the redshift of the last scattering surface (in a reionized model). A definitive test will require measurement of large angular scale anisotropy to a level σT/T ~ 3 x 10^-6^. Publication: The Astrophysical Journal Pub Date: November 1989 DOI: 10.1086/185564 Bibcode: 1989ApJ...346L...1G Keywords: Anisotropy; Baryons; Perturbation Theory; Relic Radiation; Compton Effect; Computational Astrophysics; Universe; White Noise; Astrophysics; COSMIC BACKGROUND RADIATION; COSMOLOGY full text sources ADS |

Expansion of a Thin Shell around a Void in Expanding Universe. II

Motion of a compressed shell in the dust universe model is investigated in a fully relativistic manner under the approximation of infinitesimally thin shell: All voids smaller than the horizon size expand similarly, but the voids larger than the horizon do not expand appreciably until the horizon encompasses their sizes. In the open universe model, the enlargement of the void stops actually after some period. In the flat universe, the void expands forever faster than the background and its radius R behaves asymptotically as R/a ∝t0.130, where a is the scale factor of the background universe. In the closed universe, the void expands much faster and tends to the light velocity at the final stage.