排序方式： 共有18条查询结果，搜索用时 15 毫秒
11.
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
12.
Koijam Maniharsingh 《Astrophysics and Space Science》1990,172(1):29-45
Certain new analytic solutions for slowly-rotating charged perfect-fluid universes coupled with zero-mass scalar field are found out to substantiate the possibility of the existence of rotating cosmological objects of such nature and their dynamics is investigated. The nature and role of the metric rotation (r, t) as well as that of the matter rotation (r, t) under different conditions are studied. The effects of the charged field and the scalar field on the rotational motion are also discussed. In some solutions we find out the temporal restrictions on the models for real astrophysical situations. Rotating models which are expanding as well are obtained, in which cases the rotational velocities are found to decay with the time, and these models may be taken as good examples of real astrophysical objects in this Universe. 相似文献
13.
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
14.
Manihar Singh Koijam 《Astrophysics and Space Science》1988,143(1):137-152
By considering a spherically-symmetric metric, certain new analytic solutions for charged rotating viscous-fluid cosmological models in the Einstein universe are found out. Five different cases in which the nature and role of the rotational velocity (r, t) is related to the local dragging of inertial frames and that of matter rotation (r, t), are investigated. Except for the case of perfect dragging, the electric field is found to have a damping effect on the rotation of matter. The damping effect is seen to be roughly analogous to the viscosity. In some solutions we find out the temporal restrictions for realistic astrophysical situations. Models which are rotating as well as expanding are also obtained and studied. 相似文献
15.
Koijam Manihar Singh 《Astrophysics and Space Science》1987,139(1):183-193
Certain new analytic solutions for the rotational perturbations of the Robertson-Walker universe are found out to substantiate the possibility of the existence of a rotating viscous universe with zero-mass scalar field. The values for (r, t) which is related to the local dragging of inertial frames are investigated. In all the cases the rotational velocity is found to decay with time. Except for perfect dragging the scalar field is found to have a damping effect on the rotation of matter. The damping effect is found to be roughly analogous to viscosity. In some solutions it is found that the scalar field may exist only during a time period in the course of evolution of the Universe. 相似文献
16.
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
17.
Rotational perturbations of charged cosmological viscous-fluid universes coupled with a scalar field
Manihar Singh Koijam 《Astrophysics and Space Science》1989,162(1):129-150
The dynamics of a slowly rotating charged viscous-fluid Universe coupled with a 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. The effects of charged field and scalar field on the rotational motion are discussed. Except for perfect dragging, the scalar field as well as the charged field is found to have a damping effect on the rotation of matter. Rotating models which are expanding as well are obtained, in which cases the rotational velocities are found to decay with the time, and these models may be taken as good examples of real astrophysical situations. The periods of physical validity of different models are also obtained. 相似文献
18.
Manihar Singh Koijam 《Astrophysics and Space Science》1988,149(1):149-161
One of the models which have stable limit cycles but are very close to the transition of the type I intermittency is examined in some detail. The work integrals are calculated for nonlinear oscillations with various amplitudes. The model reaches its limit cycle by saturation of the driving forces due to the ionized helium (He+) ionization. By increasing amplitudes damping becomes superior to the driving forces and so the limit cycle is stable. However, with even larger amplitudes the model becomes pulsational unstable indicating a large positive contribution to the work integral at rather deep interior. Strong luminosity drops are observed in this region during contraction phase. It is shown that the drops come from the neutral helium and hydrogen (He and H) ionization zones moved down to the deep interior at contraction phase with increasing amplitudes. A shock wave is generated by the radiation pressure at the ionization zones and propagates outwards at the phase. The zone between the ionization zones and the detached shock front is compressed locally. Thus, subsequent contraction leads the pressure at the zone becomes very high, causing remarkable enhancement of the opacities. Thus the driving becomes to work efficiently. This is a main driving force with finite amplitudes beyond the limit cycle, and makes the model to have an unstable fixed point beyond it. 相似文献