共查询到20条相似文献，搜索用时 171 毫秒
1.
A study of imperfect fluid interacting with the gravitational field for spherically-symmetric Robertson-Walker metric has been carried out. Exact solutions of the field equations of viscous fluid have been obtained under different equations of state. The corresponding physical interpretations of the solutions have been investigated. It has been shown that the occurrence of Big-Bang does not take place when the viscous fluid as only source term interacts with the gravitational field at the initial stages. 相似文献
2.
Koijam Maniharsingh 《Astrophysics and Space Science》1991,182(1):141-153
The dynamics of particle creation in the slowly rotating Robertson-Walker universe is studied by use of the Brans-Dicke theory, and four interesting solutions are obtained. Along with the discussion of the nature of the gravitational constant and other physical parameters in these model universes, the behaviour of these solutions with respect to Dirac's hypotheses are investigated. Also it is found that the expansion law is determined by the particles created by the expansion itself. Except for the case of a flat universe, the metric rotation as well as the matter rotation is found to have a damping effect on the creation of particles. 相似文献
3.
Koijam Manihar Singh 《Astrophysics and Space Science》2010,325(1):127-135
Some new interesting solutions, the dynamics, behaviour and phenomena of rotating charged perfect fluid models are investigated,
and their physical and geometrical properties are studied in order to substantiate the possibility of the existence of such
astrophysical bodies in this Universe. The nature and role of the metric rotation Ω(r,t) as well as that of the matter rotation ω(r,t) are studied for uniform and non-uniform motions. The reactions of the gravitational and charged fields with respect to the
rotational motion are studied and possible results are explored for real astrophysical situations, and in some solutions we
find the spatial restrictions on the models for realistic conditions. Rotating models which are expanding are obtained in
which the rotational motions are decaying with time. 相似文献
4.
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
5.
We obtain some cosmological models that are exact solutions of Einstein's field equations. The metric utilized is Marder's metric which is Bianchi Type I and the curvature source is a cloud of strings which are one dimensional objects. Bianchi type cosmological models play an important role in the study of the universe on a scale which anisotropy is not ignored. In this paper we have investigated the effect of cosmic strings on the cosmic microwave background anisotropy. Various physical and geometrical properties of the model are also discussed. The solutions have reported that the cosmic microwave background anisotropy may due to the cosmic strings. 相似文献
6.
M. Farasat Shamir 《Astrophysics and Space Science》2010,330(1):183-189
The modified theories of gravity, especially the f(R) gravity, have attracted much attention in the last decade. In this context, we study the exact vacuum solutions of Bianchi
type I, III and Kantowski-Sachs spacetimes in the metric version of f(R) gravity. The field equations are solved by taking expansion scalar θ proportional to shear scalar σ which gives A=B
n
, where A and B are the metric coefficients. The physical behavior of the solutions has been discussed using some physical quantities. Also,
the function of the Ricci scalar is evaluated in each case. 相似文献
7.
Manihar Singh Koijam 《Astrophysics and Space Science》1989,161(1):111-123
Certain new analytic solutions for rotating perfect-fluid spheres in the Robertson-Walker universe are found out to substantiate the possibility of the existence of rotating cosmological objects coupled with zero-mass scalar field. Exact solutions for the metric rotation (r, t) and the matter rotation (r, t) under different conditions are obtained and their nature and role are investigated. Except for perfect dragging the scalar field is found to have a damping effect on the rotation of matter. In some solutions we find out the restrictions on the radii of the models for realistic astrophysical situations. Rotating models which can also be expanding are also obtained, in which case the rotational velocities are found to decay with the time; and these models may be taken as examples of real astrophysical objects in the Universe. 相似文献
8.
Solutions of Brans-Dicke field equations are obtained when the source of the gravitational field is a perfect fluid with pressure equal to energy density and the metric is cylindrically symmetric of Marder-type. Various physical and geometrical properties of the model have been discussed. Finally the solutions have been transformed to the original form of Brans-Dicke (1961) theory and then through unit transformation to a general form. 相似文献
9.
Koijam Maniharsingh 《Astrophysics and Space Science》1991,182(2):207-219
The dynamics of a slowly-rotating cosmological viscous-fluid universe is investigated and the rotational perturbations of such models are studied in order to substantiate the possibility that the Universe is endowed with slow rotation, in the course of presentation of some new analytic solutions. Three different cases are taken up in which the nature and role of the metric rotation (r, t) as well as that of the matter rotation (r, t) are discussed. The periods of physical validity of some of the models and the effect of viscosity on the rotational motion are also found out. Rotating models which are expanding as well are obtained, where in all the cases the rotational velocities are found to decay with the time; and these models may be taken as good examples of real astrophysical situations. 相似文献
10.
The present study deals with the inhomogeneous plane symmetric models in scalar-tensor theory of gravitation. We used symmetry group analysis method to solve the field equations analytically. A new class of similarity solutions have been obtained by considering the inhomogeneous nature of metric potential. The physical behavior and geometrical aspects of the derived models are also discussed. 相似文献
11.
This paper is devoted to the study of role of particle creation and bulk viscosity on evolution of homogeneous and anisotropic
model of the universe represented by Bianchi type I space time metric. Particle creation and bulk viscosity have been considered
as separated irreversible processes. In order to discuss physical and geometrical behaviour of the model, a new set of exact
solutions of Einstein’s field equation have been obtained in non-causal, truncated and full causal theories. Dynamical behaviours
of models have also been discussed. 相似文献
12.
Koijam Manihar Singh 《Astrophysics and Space Science》2010,325(2):293-302
Investigations are made on slowly rotating radiating Universes coupled with a scalar field in the spherically symmetric Einstein
formalism, and some new interesting solutions are obtained. Their physical and geometrical properties are studied from various
angles. The rotational perturbations of such models are examined in order to substantiate the possibility that the universe
is endowed with some rotation. The nature and role of the metric rotation as well as that of the rotation of matter are studied,
and the effects of radiation and scalar fields on them are discussed. The models here turn out to be rotating as well as expanding
ones, which may be taken as good examples of real astrophysical objects in this universe. The periods of the physical validity
and the restrictions on the radii of the models for real astrophysical situations are obtained and discussed. The models obtained
here are theoretically satisfactory and therefore there is a possibility that there may be less known objects in this universe
which may be represented by our model Universes obtained here and many unknown properties of this universe may be explored
and unfolded in the study of these models. 相似文献
13.
The problem of electromagnetic field interacting with viscous fluid without and with zero-mass scalar field has been studied. It has been shown that electromagnetic field cannot interact with viscous fluid for spherically-symmetric Robertson-Walker metric. Exact solutions corresponding to the problem of electromagnetic field interactions in presence of viscous fluid and zero-mass scalar field have been obtained subject to various physical conditions. It presents a scope for the study of imperfect fluid FRW models showing the existence of the electromagnetic field due to the presence of zero-mass scalar field. 相似文献
14.
Koijam Manihar Singh 《Astrophysics and Space Science》2009,323(3):297-306
Presenting some interesting new solutions, rotating models of anisotropic two-fluid universes coupled with a magnetic field
are investigated and studied, where the anisotropic pressure is generated by the presence of two non-interacting perfect fluids
which are in relative motion with respect to each other. Here special discussion is made of the physically interesting class
of models in which one fluid is a comoving radiative perfect fluid which is taken to model the cosmic microwave background
and the second a non-comoving perfect fluid which will model the observed material content of the universe. Besides studying
their physical and dynamical properties the effects of rotation on these models are studied and the reactions of the magnetic
and gravitational fields with respect to the rotational motion are discussed. Analysis on the rotational perturbations are
also made, in the course of which the amount of anisotropy induced in pressure distribution by a small deviation from the
Friedmann metric is also investigated. The models obtained here are found to be theoretically satisfactory and thereby substantiates
the possibilities of existence of such astrophysical objects in this Universe and may be taken as good examples of real astrophysical
situations. 相似文献
15.
Static and spherical symmetric solutions of the field equations in the bimetric general theory of gravitation are obtained
for perfect and anisotropic charged fluids under the assumption that the physical metric admits a one-parameter group of conformal
motion. All solutions are matched to the Reissner–Nordstrom metric and possess positive energy density larger than the stresses,
everywhere within the sphere. The solution agrees with Einstein’s general relativity for a physical system comparable to the
size of the universe, such as the solar system. 相似文献
16.
The Brans-Dicke field equations for a perfect fluid distribution representing slowly rotating fluid spheres are investigated. Exact solutions are obtained for differential rotation and perfect dragging by imposing some physical restrictions on the matter rotation (r,t). The physical properties are discussed fork=±1. 相似文献
17.
The Brans-Dicke field equations for a viscous distribution representing slowly rotating fluid spheres are investigated. Exact solutions are obtained for differential rotation by imposing physical restrictions on the matter rotation (r,t). The physical properties are discussed fork=±1. 相似文献
18.
Tapas K.Das 《Monthly notices of the Royal Astronomical Society》2002,330(3):563-566
The equations governing general relativistic, spherically symmetric, hydrodynamic accretion of polytropic fluid on to black holes are solved in the Schwarzschild metric to investigate some of the transonic properties of the flow. Only stationary solutions are discussed. For such accretion, it has been shown that real physical sonic points may form even for flow with γ <4/3 or γ >5/3 . The behaviour of some flow variables in the close vicinity of the event horizon is studied as a function of specific energy and the polytropic index of the flow. 相似文献
19.
Static and spherically-symmetric solutions of the field equations in the bimetric theory of gravitation are obtained for isotropic and anisotropic distributions of matter when the physical metric admits a one-parameter group of conformal motions. The solutions agree with Einstein's general relativity for physical systems comparable to the size of the Universe, such as the solar system. 相似文献
20.
Koijam Maniharsingh 《Astrophysics and Space Science》1991,180(2):253-271
The dynamics of slowly rotating magneto-viscous fluid universe coupled with zero-mass scalar field is investigated, and the rotational perturbations of such models are studied in order to substantiate the possibility that the Universe is endowed with slow rotation, in the course of presentation of several new analytic solutions. Four different cases are taken up in which the nature and role of the metric rotation (r, t) as well as that of the matter rotation(r,t) are discussed. Except for the case of perfect drag, the scalar field is found to have a damping effect on the rotational motion. This damping effect is seen to be roughly analogous to the viscosity. The periods of physical validity of some of the models are also found out. Most of the rotating models obtained here come out to be expanding ones as well which may be taken as good examples of real astrophysical situations. 相似文献