共查询到20条相似文献，搜索用时 15 毫秒
1.
In an earlier paper Arp, Bi, Chu and Zhu investigated various quasar samples and recognized a periodicity of remarkable degree in them. Their conclusion was that the existence of such a periodicity is a counterevidence against the cosmological origin of quasar redshifts. Since this question is of great importance in a cosmological context, here we reanalyze some of the samples together with a galaxy sample of the pencil-beam survey of Broadhurstet al. Our result is that on the plane of cosmological parameters (0, 0) there is a non-negligible region where two quasar samples and the galaxy sample are simultaneously fairly periodic. Pure periodicity is still compatible with cosmological principles, at least on length scales much longer than the period length. So the regularities can fit into a cosmological context. 相似文献
2.
Relativistic cosmological field equations are obtained for a non-static stationary Bertotti-Robinson-type space-time for interacting perfect fluid and electromagnetic field. The cosmological solution to the field equations are obtained and the nature of the electromagnetic field as well the perfect fluid are studied. The electromagnetic field generated here corresponds to a special generic case and the perfect fluid distribution degenerates into a barotropic perfect fluid with equation of statep+=0, >0. It is shown here that the interacting barotropic fluid can generate gravitation only when the cosmological constant being a function ofx in a dynamic field. 相似文献
3.
Miloslav Dubec 《Astrophysics and Space Science》1991,175(2):207-213
A theory of gravitation in a flat space is briefly described, which gives a completely new view on cosmological problems. Instead of expansion of the Universe, a contraction of bodies and clusters is obtained. This theory excludes the closed solutions as non-physical ones and gives a simple condition for the stability of gravitationally-bounded systems with respect to cosmological gravitational field. 相似文献
4.
Exponential and power law solutions for homogeneous cosmological modelshave been discussed in a generalized scalar-tensor theory where both thecosmological term and coupling parameter are taken tobe functions of the scalar field , along with the bulk viscousstress of the cosmic fluid. Assuming simple relationships of the scalarfield with the cosmological term and the coupling parameter, all thesolutions are studied in Dicke's revised units. By use of a conformaltransformation, the solutions are also expressed in atomic units. 相似文献
5.
Harald H. Soleng 《Astrophysics and Space Science》1987,136(1):109-111
An example of a cosmological model with variable gravitational couplingG and a time-dependent cosmological term , has recently been presented. It has been shown that there is no creation of matter and that the rest mass of particles stays constant in this model. In this paper we will generalize the field equations to the case where bothG and depend both on time and position. It is shown that even in this case there may be no creation. 相似文献
6.
The perturbation by a spherical rotating shell is investigated in a homogeneous and isotropic cosmological model of viscous fluid distribution to first order in angular velocity (r, t) of matter and the metric rotation function (r, t) which is uniform and non-uniform the exact solutions for (r, t) are obtained for all cosmological models. The physical properties of these solutions are discussed. 相似文献
7.
M.G. Larionov 《Astrophysics and Space Science》1997,252(1-2):139-149
The possibility of using a Friedmann-Lemaître model with a non-zero cosmological constant is investigated on the basis of analyses of the RATAN-600 and 87GB radio surveys and optical constraints. A zero deceleration parameter and critical matter density are features of the model. The model is in agreement with current observational data, including estimates of the age of the Universe, Hubble constant measurements, and the - z relation. A value for the cosmological constant is determined and its physical nature discussed. 相似文献
8.
J. G. Laros 《Astrophysics and Space Science》1996,244(1-2):105-109
Gamma-Ray Burst (GRB) locations are distributed isotropically on the sky, but the intensity distribution of the bursts seems clearly incompatible with spatial homogeneity. Of the scenarios that attempt to provide an explanation, there are two that enjoy current popularity: (1) GRBs are produced by high-velocity neutron stars that have formed an extended (100 kpc) spherical halo or corona around our galaxy. (2) The bursters are at cosmological distances, with redshifts near unity for the weaker events. The major evidence used to argue for or against each of these scenarios remains inconclusive. Assuming, not unreasonably, that the cosmological scenario is correct, one can discuss the advantages and disadvantages of studying GRBs as opposed to other objects at moderate redshift. We find that the advantages of GRBs-high intensity, penetrating radiation, rapid variability, and no expected source evolution-are offset by observational difficulties pertaining to the extraction of cosmological information from GRB data. If the cosmological scenario proves to be correct and if the observational difficulties are overcome, then cosmologists certainly should care. 相似文献
9.
Einstein field equations are considered for zero-curvature Robertson-Walker models in the case of a viscous fluid distribution interacting with zero-rest-mass scalar fields. Exact solutions are obtained for two different phases of the early universe viz. the inflationary phase and the radiation-dominated phase, by using the 'gamma-law' equation of state p = (-1). The index describing the material content varies continuously with cosmological time. The gravitational 'constant' and bulk viscosity are both allowed to depend on the cosmic time. Some physical properties of the cosmological models are also discussed. 相似文献
10.
Robertson-Walker cosmological model with bulk viscosity is investigated with equation of statep=(–1). The cosmological solution of the model is obtained with the help of the special law of variation for Hubble's deceleration parameter. Some physical consequences of the solution is studied pertaining to two extreme cases of the equation of state. 相似文献
11.
S. Bellert 《Astrophysics and Space Science》1977,47(2):263-276
Rust (1974) stated that the classical (e.g., Doppler) explanations of the cosmological red shift contradict the results of astronomical observations of the period of changes in the brightness of supernovae. This paper is an attempt at explaining this discrepancy between observations and the theoretical predictions on the grounds of a hypothesis published by the author (Bellert, 1969). That hypothesis explains the cosmological red shift by the geometry of the space of events, which is a static space.We regret to report that, soon after the submission of this paper, Professor Bellert passed away on 27 March, 1976 in Warsaw. 相似文献
12.
Some Bianchi type I viscous fluid cosmological models with a variable cosmological constant are investigated in which the
expansion is considered only in two direction i.e. one of the Hubble parameter
is zero. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density whereas the coefficient
of shear viscosity is considered as constant in first case whereas in other case it is taken as proportional to scale of expansion
in the model. The cosmological constant Λ is found to be positive and is a decreasing function of time which is supported
by results from recent supernovae Ia observations. Some physical and geometric properties of the models are also discussed. 相似文献
13.
Cosmological solutions that obey the perfect fluid equation of state in Wesson's gravitational theory are presented assuming that the fifth dimension subspace is also homogeneous and isotropic like the usual homogeneous isotropic cosmological model. It is shown that the scale factor scales as
for the vanishing fifth component of the energy momentum tensor. The role of the fifth component as a cosmological constant is remarked, and an inflationary model is thus obtained. 相似文献
14.
Ivan I. Shevchenko 《Astrophysics and Space Science》1993,202(1):45-56
For the case of closed Friedmann models with the cosmological constant, an N - dependence is plotted, whereN is the conformal time of existence of the Universe, and is the ratio of the cosmological constant to its Einstein's value. The observational properties of the asymptotic model of the first kind (the so-called Al model) corresponding to the maximum of this dependence are analyzed. For the matter-dominated models, the maximum is achieved at the point = 1. Formulae for the calculation of the age of the Universe and for that of the photometric distance in the Al model are deduced. The observational properties of the A1 model are compared to the corresponding properties of the standard cosmological model ( = 0) which does not occupy any special distinguished position on the N - diagram. It is shown that from the standpoint of the modern observational cosmology these two models cannot be told one from another. However, the A1 model has better standing from the viewpoint of the strong wordings of the anthropic cosmological principle. 相似文献
15.
In this paper basic cosmological consequences of zatrikean pregeometry are studied. It is shown that many universal quantities can be calculated with simple applications of this theory. An equation directly linking the angular velocity of the universe, the Hubble constantH and the mean density of the universe is derived. The relation between the massM and the radiusR of the universe is examined. This relation leads to various cosmological scenarios, including variations in physical constants and/or violation of the mass conservation and/or variable geometrical properties. 相似文献
16.
We present a class of exact cosmological solutions of Brans-Dicke (B-D) equations with cosmological constant in flat Robertson-Walker metric. These solutions are based on the relation øR
n= constant between the B-D field and the scale factor of the universe. This relation turns out to be consistent with the equation of statep =m for the cosmic matter, provided thatn andm are suitably related to each other. Several special cases and asymptotic solutions are derived and discussed. 相似文献
17.
The origin of discrepancy between the observed redshift dependence of the angular size of double radio sources and the relation expected for constant diameter objects in homogenous relativistic cosmologies is reconsidered. A correlation between absolute magnitude and projected linear separation for the sources could account for this discrepancy by observational selection without requiring cosmological evolution of the entire source population. We conclude that it is premature to use the -z test as support either for astrophysical models of double radio source evolution, or for particular cosmological models. 相似文献
18.
Ewa Rydzyńska 《Astrophysics and Space Science》1989,159(1):11-19
In this paper we prove an equivalence of velocity and Bellert's dilatation of metric. It is the kind of principle such as the equality of gravitational and inertial masses, noted by Newton, or equivalence of acceleration and space curvature, proved by Einstein. Our equivalence can be a foundation of a new theory, as it was in the two mentioned cases.The result is presented in two ways. One of these is a comparison of cosmological theories; and a dependence between the most important cosmological models is obtained. In this paper one of the results from the previous paper of the author (Rydzyska, 1989) is corrected. 相似文献
19.
We use the generalized Brans-Dicke theory, in which the Pauli metric is identified to be the physical space-time metric, to study the Universe in different epochs. Exact analytical expressions for dilaton field , cosmological radiusR and density parameter are obtained fork=+1,0,–1 Universe in the radiation-dominated epoch. For matter dominated Epoch, exact analytical expressions for Hubble parameterH, cosmological radius, dilaton field, deceleration factorq, density parameter and the gravitational coupling of the ordinary matter are obtained for the flat Universe. Other important results are: (1) the density parameter is always less than unity for the flat Universe because the dilaton field plays a role as an effective dark matter, and (2) the new Brans-Dicke parameter must be larger than 31.75 in order to consistent with the observed data. 相似文献
20.
We review models of cosmological gamma-ray bursts (GRBs). The statistical and -ray transparency issues are summarized. Neutron-star and black-hole merger scenarios are described and estimates of merger rates are summarized. We review the simple fireball models for GRBs and the recent work on non-simple fireballs. Alternative cosmological models, including models where GRBs are analogs of active galactic nuclei and where they are produced by high-field, short period pulsars, are also mentioned. The value of neutrino astronomy to solve the GRB puzzle is briefly reviewed. 相似文献