Showing papers on "Dark fluid published in 1986"

Dark matter in the universe.

Abstract: What is the universe made of? What kind of matter is com­ monest, how much is there and how is it distributed? These ques­ tions, always a focus of cosmology, have become even more intriguing over the past few years as evidence has piled up to support the proposition that most of the mass in the universe is dark-invisible to any existing tele­ scope or other observational device­ and new developments in both high­ energy physics and astrophysics have made possible new predictions of the makeup and distribution of this possi­ bly exotic form of matter. There is already overwhelming evi­ dence that the visible matter within galaxies may account for less than 10 percent of the galaxies' actual mass: the rest, not yet directly detectable by observers on the earth, is probably dis­ tributed within and around each gal­ axy. Theoretical considerations now suggest this may be only the tip of the cosmic "iceberg" of dark matter: much greater amounts of dark matter may be distributed throughout the uni­ verse, perhaps in configurations en­ tirely independent of the distribution of galaxies. It may be that this mass can be accounted for only by the exis­ tence of new kinds of matter. The question of dark matter-how much of it there is, how it is distributed and what it is made of-is intimately linked to questions about the overall structure and evolution of the uni­ verse: because dark matter is probably the dominant form of mass in the uni­ verse, it must have affected the evolu­ tion of the features observable today. Questions of structure in turn depend for their answers on a deep bond that has formed between macro physics and microphysics, the bodies of knowledge that respectively describe interactions on the largest scale (that of the uni­ verse as a whole) and the smallest scale (that of the fundamental particles that make up all matter).

Towards a Physical Model for Galactic Rotation Curves

Abstract: Extensive and meticulous observations of the rotation curves of galaxies show that they are either flat or gently going up, but rarely decreasing, at large galactocentric distances. Here we show that the gravitational potential which would lead to such rotation curves arises naturally when the visible matter modelled as a collisionless Maxwellian gas is embedded in a dark halo of collisionless particles with a much higher dispersion in velocities.

A new approach to the problem of dark matter

Abstract: The properties of X’s (the elementary constituents of dark matter) are chosenad hoc with the primary aim of solving three troublesome astrophysical puzzles : a X should have a mass larger than 4 proton masses and a collision cross-section with nucleons of ~ 2.10-37 cm2; easily escaping « dark radiation » could be emitted in a collision. X’s would steadily accrete into stars and concentrate in their cores; they would speed up significantly the evolution of low-mass stars and modify the final scenario. The71Gra neutrino experiment should allow definite conclusions concerning the presence of X’s in the Sun.

The self-similar cosmological paradigm; galactic scale phenomena and the «dark matter»

Abstract: Empirical estimates for the radii, velocity distribution, rotation periods and masses of galaxies are compared with predictions derived from a self-similar cosmological model previously presented by the author. This model also predicts the existence of an undiscovered class of stellar objects that may account for the enigmatic "dark matter", which is known to be the dominant constituent of galaxies but which has yet to be identified.

Dark matter, cosmic strings, and large scale structure

Abstract: Although the hypothesis of cold dark matter with a Zeldovich spectrum of primordial Gaussian fluctuations appears to give a picture of galaxy and cluster formation that is in reasonably good agreement with the available observations, there are indications that this model leads to less structure on very large scales than is observed. This paper gives a progress report on our efforts to study the formation of large scale structure in models with either (a) an additional feature in the fluctuation spectrum on large scales, such as can arise in a hybrid model with comparable amounts of baryonic and cold dark matter, or (b) non-Gaussian fluctuations, for example those that arise from cosmic strings. Although we cannot yet tell whether either approach will ultimately be sucessful, our preliminary results confirm that cosmic strings can lead to the sorts of rich cluster correlations that are observed.

Dynamical effects of dark matter in systems of galaxies

Abstract: SeveralN-body experiments were performed in order to simulate the dynamical behaviour of systems of galaxies gravitationally dominated by a massive dark background We discuss mass estimates from the dynamics of the luminous component (M VT) under the influence of such a background, assuming a constant dark/luminous mass ratio (M D/M L) and plausible physical conditions We extend in this way previous studies (Smith, 1980, 1984) about the dependence ofM VT on the relative distributions of dark and luminous matter (Limber, 1959) We found that the observed ratio of the virial theorem mass to luminosity (M VT/L) in systems of galaxies of different sizes could be the result of different stages of their post-virialisation evolution as was previously suggested by White and Rees (1978) and Barnes (1983) This evolution is mainly the result of the dynamical friction that dark matter exerts on the luminous component Thus our results give support to the idea that compact groups of galaxies are dynamically more evolved than large clusters, which is expected from the ‘hierarchical clustering’ picture for the formation of such structures

Weak Interaction and the Large Scale Structure of the Universe

Abstract: The combined problems of large scale structure, the need for non-baryonic dark matter if Ω = 1, and the need to make galaxies early in the history of the universe seem to be placing severe constraints on cosmological models. In addition, it is shown that the bulk of the baryonic matter is also dark and must be accounted for as well. The nucleosynthesis arguments are now strongly supported by high energy collider experiments as well as astronomical abundance data. The arguments for dark matter are reviewed and it is shown that observational dynamical arguments and nucleosynthesis are all still consistent at Ω ~ 0.1. However, the inflation paradigm requires Ω = 1, thus, the need for non-baryonic dark matter. A non-zero cosmological constant is argued to be an inappropriate solution. Dark matter candidates fall into two categories, hot (neutrino-like) and cold (axion or massive photino-like). New observations of large scale structure in the universe (voids, foam, and large scale velocity fields) seem to be most easily understood if the dominant matter of the universe is in the form of low mass (9eV ≤ m ν ≤ 35eV) neutrinos. Cold dark matter, even with biasing, seems unable to duplicate the combination of these observations (of particular significance here are the large velocity fields, if real). However, galaxy formation is difficult with hot matter.

Dark matter and cosmological nucleosynthesis

Abstract: It is shown that big bang nucleosynthesis requires at least some of the baryons in the universe must be dark. All current solutions seem to require at least two ad hoc assumptions. Of these more complex but complete solutions, the ability to produce large scale free structures where these dark baryons lie may be the best way to resolve the different proposed solutions to the several different dark matter problems.