共查询到20条相似文献，搜索用时 32 毫秒
1.
We have obtained static and spherically symmetric self-gravitating solution of the field equations for anisotropic distribution of matter in higher- dimensional in the context of Einstein’s general theory of relativity. This work is an extension of the previous work of Hector Rago (Astrophys. Space Sci. 183:333, 1991) for four dimensional space-time. The solutions are matched to the analytical solutions for spherically symmetric self gravitating distribution of anisotropic matter obtained by Hector Rago (1991) for n=2. 相似文献
2.
The present study deals with spatial homogeneous and anisotropic locally rotationally symmetric (LRS) Bianchi-II dark energy model in general relativity. The Einstein’s field equations have been solved exactly by taking into account the proportionality relation between one of the components of shear scalar $(\sigma^{1}_{1})$ and expansion scalar (?), which, for some suitable choices of problem parameters, yields time dependent equation of state (EoS) and deceleration parameter (DP), representing a model which generates a transition of universe from early decelerating phase to present accelerating phase. The physical and geometrical behavior of universe have been discussed in detail. 相似文献
3.
The exact higher dimensional solutions of Einstein-Maxwell field equations for spherically symmetric distribution of charged perfect fluid are obtained by using the method originally used by Hajj-Boutros and Sfeila (Gen. Relativ. Gravit. 18(4):395, 1986) for four-dimensional space-time. The new exact solutions have been generated from those of Khadekar et al. (J. Indian Math. Soc. 68(1–4):33, 2001), Humi and Mansour (Phys. Rev. D 29(6):1076, 1984) and Banerjee and Santos (J. Math. Phys. 22(4):824, 1981) in the frame work of higher dimensional space-time. The various physical properties are also discussed. 相似文献
4.
P. Chauvet 《Astrophysics and Space Science》1983,90(1):51-58
By a rescalation of the scalar field ? of the Jordan-Brans and Dicke cosmology, the general solutions of the Friedmannian ‘vacuum’ Universe are obtained. Only the flat space solution was previously known. Each solution is caracterized by the sign of the second time derivative of the rescaled field ψ≡?R 3 (R being the scale factor of the Robertson-Walker line-element): \(\ddot \psi\) = 0 (flat space), \(\ddot \psi\) < 0 (closed space), and \(\ddot \psi\) > 0 (open space), so that the solutions are mutually exclusive. Of these, the open space one is damped-oscillatory andR attains its absolute minimum, equal to zero, in only one of the two ‘extreme’ cycles. Otherwise,R min remains positive. If the ?-field is dominant near the singularity, these solutions may have physical significance. Also obtained, by the method mentioned above, is the general flat space solution for a ‘dust’ Universe and from it a closed space ‘dust’ solution. Both were found before by different authors, each one using a different method and, therefore, seemed up to now unrelated. 相似文献
5.
Demetrios D. Dionysiou 《Astrophysics and Space Science》1982,88(2):493-499
A spherically-symmetric static scalar field in general relativity is considered. The field equations are defined by $$\begin{gathered} R_{ik} = - \mu \varphi _i \varphi _k ,\varphi _i = \frac{{\partial \varphi }}{{\partial x^i }}, \varphi ^i = g^{ik} \varphi _k , \hfill \\ \hfill \\ \end{gathered} $$ where ?=?(r,t) is a scalar field. In the past, the same problem was considered by Bergmann and Leipnik (1957) and Buchdahl (1959) with the assumption that ?=?(r) be independent oft and recently by Wyman (1981) with the assumption ?=?(r, t). The object of this paper is to give explicit results with a different approach and under a more general condition $$\phi _{;i}^i = ( - g)^{ - 1/2} \frac{\partial }{{\partial x^i }}\left[ {( - g)^{1/2} g^{ik} \frac{\partial }{{\partial x^k }}} \right] = - 4\pi ( -g )^{ - 1/2} \rho $$ where ?=?(r, t) is the mass or the charge density of the sources of the field. 相似文献
6.
Giulio Calamai 《Astrophysics and Space Science》1970,6(2):240-257
The second variation of the mass-energy (by constant baryon number) is analysed to inquire into the stability of the equilibrium for a spherical mass under the action of its own gravitation. The equations of general relativity are used. For zero density at the surface, the sphere is stable if (and only if) a solution of a second order equation (Jacobi equation) has only one zero in the interior (at center) of the sphere. The results obtained in this way coincide of course with those obtained by means of the Chandrasekhar-Misner-Zapolsky variational principle, but the solution of the Jacobi equation is more simple and straightforward. In particular, the stability of the several modes are analysed without making any choice of a trial function for the Lagrangian displacement.The method is applied to the GrattonR-polytropic model of supermassive stars.Work done in the Laboratorio Astrofisico, Frascati-Roma, Italy. 相似文献
7.
A spatially homogeneous and anisotropic Bianchi type-VI0 space-time filled with perfect fluid in general relativity and also in the framework of f(R,T) gravity proposed by Harko et al. (in arXiv:1104.2669 [gr-qc], 2011) has been studied with an appropriate choice of the function f(R,T). The field equations have been solved by using the anisotropy feature of the universe in Bianchi type-VI0 space time. Some important features of the models, thus obtained, have been discussed. We noticed that the involvement of new function f(R,T) doesn’t affect the geometry of the space-time but slightly changes the matter distribution. 相似文献
8.
Pavel Voráček 《Astrophysics and Space Science》1982,81(1-2):85-94
Four situations are shown where the Schwarzschild metric cannot be used or is subject to unsurmountable problems. The first is the question of a metric useful for PPN-formalism checking different gravitational theories. The second problem occurs in connection with Mach's principle, when the flatness of the spacetime inside a massive hollow sphere is a generally accepted solution. The metrical discontinuity on the same spherical shell is a third problem. The fourth one is the anisotropy of the mass-energy of a test particle in the gravitational field. Three principles for solution are proposed:
- The space is not dilated, but rather contracted, in the gravitational field; then the measurement-rods are shorter and measured distances have greater magnitudes.
- The potential energy is to be related to a potential level where a stationary observer is placed and the general relativistic potential must be used.
- A new metric must be introduced which is distinct from the Schwarzschild metric, so that the space in the gravitational field is warped isotropically.
9.
The first post-Newtonian approximation of general relativity is used to account for the motion of solar system bodies and near-Earth objects which are slow moving and produce weak gravitational fields. The \(n\)-body relativistic equations of motion are given by the Einstein-Infeld-Hoffmann equations. For \(n=2\), we investigate the associated dynamics of two-body systems in the first post-Newtonian approximation. By direct integration of the associated planar equations of motion, we deduce a new expression that characterises the orbit of test particles in the first post-Newtonian regime generalising the well-known Binet equation for Newtonian mechanics. The expression so obtained does not appear to have been given in the literature and is consistent with classical orbiting theory in the Newtonian limit. Further, the accuracy of the post-Newtonian Binet equation is numerically verified by comparing secular variations of known expression with the full general relativistic orbit equation. 相似文献
10.
Markus J. Aschwanden 《Journal of Astrophysics and Astronomy》2008,29(1-2):3-16
Celebrating the diamond jubilee of the Physics Research Laboratory (PRL) in Ahmedabad, India, we look back over the last six decades in solar physics and contemplate on the ten outstanding problems (or research foci) in solar physics:
- The solar neutrino problem
- Structure of the solar interior (helioseismology)
- The solar magnetic field (dynamo, solar cycle, corona)
- Hydrodynamics of coronal loops
- MHD oscillations and waves (coronal seismology)
- The coronal heating problem
- Self-organized criticality (from nanoflares to giant flares)
- Magnetic reconnection processes
- Particle acceleration processes
- Coronal mass ejections and coronal dimming
11.
The problem of finding nonsingular charged analogue of Schwarzschild’s interior solutions has been reduced to that of finding a monotonically decreasing function f. The models are discussed in generality by imposing reality condition on f. It is shown that the physical solutions are possible only for surface density to central density ratio greater than or equal to 2/3 i.e. $\frac{\rho_{a}}{\rho_{0}}\ge2/3$ . The unphysical nature of solutions with linear equation state has been proved. A generalization procedure has been utilized to generalize solutions by Guilfoyle (1999). Recently found solutions by Gupta and Kumar (2005a, 2005b, 2005c) are generalized by taking particular form of f and seen to have higher mass and more stable. The maximum mass is found to be 1.59482 M Θ . The models have been found to be stable once the physical requirements are established due to mass to radius less than 4/9, total charge to total mass ratio less than 1 and redshift quite low. 相似文献
12.
Jörg Waldvogel 《Celestial Mechanics and Dynamical Astronomy》1982,28(1-2):69-82
The planar problem of three bodies is described by means of Murnaghan's symmetric variables (the sidesa j of the triangle and an ignorable angle), which directly allow for the elimination of the nodes. Then Lemaitre's regularized variables \(\alpha _j = \sqrt {(\alpha ^2 - \alpha _j )}\) , where \(\alpha ^2 = \tfrac{1}{2}(a_1 + a_2 + a_3 )\) , as well as their canonically conjugated momenta are introduced. By finally applying McGehee's scaling transformation \(\alpha _j = r^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-0em} 2}} \tilde \alpha _j\) , wherer 2 is the moment of inertia a system of 7 differential equations (with 2 first integrals) for the 5-dimensional triple collision manifold \(T\) is obtained. Moreover, the zero angular momentum solutions form a 4-dimensional invariant submanifold \(N \subset T\) represented by 6 differential equations with polynomial right-hand sides. The manifold \(N\) is of the topological typeS 2×S 2 with 12 points removed, and it contains all 5 restpoint (each one in 8 copies). The flow on \(T\) is gradient-like with a Lyapounov function stationary in the 40 restpoints. These variables are well suited for numerical studies of planar triple collision. 相似文献
13.
B. Kuchowicz 《Astrophysics and Space Science》1976,40(1):167-181
In axially-symmetric cosmological models of the Einstein-Cartan theory (which may be briefly called general relativity plus spin), the axis of symmetry is at the same time the direction of the magnetic field, and of the aligned spins. The general set of relevant equations is given. Some exact solutions of this set constitute quasi-Euclidean and semiclosed cosmologies with a uniform magnetic field and aligned spinning matter. In contrast to the situation in the framework of general relativity, one may obtain non-singular solutions. Such a behaviour of the solutions of the Einstein-Cartan theory is rendered possible by the specific spin-spin repulsive interaction which is inherent in the theory. 相似文献
14.
Markus J. Aschwanden 《Solar physics》2013,287(1-2):323-344
We derive an analytical approximation of nonlinear force-free magnetic field solutions (NLFFF) that can efficiently be used for fast forward-fitting to solar magnetic data, constrained either by observed line-of-sight magnetograms and stereoscopically triangulated coronal loops, or by 3D vector-magnetograph data. The derived NLFFF solutions provide the magnetic field components B x (x), B y (x), B z (x), the force-free parameter α(x), the electric current density j(x), and are accurate to second-order (of the nonlinear force-free α-parameter). The explicit expressions of a force-free field can easily be applied to modeling or forward-fitting of many coronal phenomena. 相似文献
15.
We study the effects of winds on advection dominated accretion flows in the presence of a global magnetic field under a self-similar treatment. The disk gas is assumed to be isothermal. For a steady state structure of such accretion flows a set of self similar solutions are presented. We consider the wind in a general magnetic field with three components (r,φ,z) in advection-dominated accretion flows. The mass-accretion rate $\dot{M}$ decreases with radius r as $\dot{M}\propto r^{s+1/2}$ , where s is an arbitrary constant. We will see, by increasing the wind parameter s, radial and rotational velocities increase. 相似文献
16.
In this paper we formulate the problem of the collapse of a spherically-symmetric, radiating body in general relativity. The requirement that the metric and its normal derivative be continuous across the boundary imposes conditions upon the evolution of the star and allows identification of physical phenomena measured by a distant observer. A solution to Einstein's field equations for the exterior of a spherically-symmetric radiating body is that derived originally by Vaidya in 1951. By requiring the continuity described above we identify the mass, luminosity, velocity, and time increment measured by a distant observer in terms of the metric parameters evaluated in a frame comoving with the outer boundary. We also assume that the interior metric is a sum of products of functions of the radius and time. The continuity requirements allow the evolution of two of the three functions of time to be determined. The evolution of the third function, describing the motion of the core, is determined by the imposition of an equation of state at the center. The adiabatic index derived from the Baym-Bethe-Pethick equation of state was used to provide this last equation. A major result is obtaining an analytic solution to Einstein's field equations describing the core of a collapsing star. As a consequence of this solution we found that for the relatively small values of the adiabatic index (max1.6), the star smoothly made the transition to a final collapsed state. Neither bounce nor shock wave was obtained. Also, there is a readily understood connection between the adiabatic index, and such parameters of the edge of the core as the velocity and acceleration. Finally, the analytic solutions provide the time-scales for the collapse which are significantly different from that of free-fall. The retarding effects of pressure upon the collapse are apparent. It is hoped that such analytic solutions will provide insight into more complicated dynamic systems in general relativity. 相似文献
17.
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
18.
Wen-Rui Hu 《Astrophysics and Space Science》1983,97(2):353-367
In Paper I (Hu, 1982), we discussed the the influence of fluctuation fields on the force-free field for the case of conventional turbulence and demonstrated the general relationships. In the present paper, by using the approach of local expansion, the equation of average force-free field is obtained as (1+b)?×B 0=(α#x002B;a)B 0#x002B;a (1)×B 0#x002B;K. The average coefficientsa,a (1),b, andK show the influence of the fluctuation fields in small scale on the configurations of magnetic field in large scale. As the average magnetic field is no longer parallel to the average electric current, the average configurations of force-free fields are more general and complex than the usual ones. From the view point of physics, the energy and momentum of the turbulent structures should have influence on the equilibrium of the average fields. Several examples are discussed, and they show the basic features of the fluctuation fields and the influence of fluctuation fields on the average configurations of magnetic fields. The astrophysical environments are often in the turbulent state, the results of the present paper may be applied to the turbulent plasma where the magnetic field is strong. 相似文献
19.
Attitude stability of spacecraft subjected to the gravity gradient torque in a central gravity field has been one of the most fundamental problems in space engineering since the beginning of the space age. Over the last two decades, the interest in asteroid missions for scientific exploration and near-Earth object hazard mitigation is increasing. In this paper, the problem of attitude stability is generalized to a rigid spacecraft on a stationary orbit around a uniformly-rotating asteroid. This generalized problem is studied via the linearized equations of motion, in which the harmonic coefficients $C_{20}$ and $C_{22}$ of the gravity field of the asteroid are considered. The necessary conditions of stability of this conservative system are investigated in detail with respect to three important parameters of the asteroid, which include the harmonic coefficients $C_{20}$ and $C_{22}$ , as well as the ratio of the mean radius to the radius of the stationary orbit. We find that, due to the significantly non-spherical shape and the rapid rotation of the asteroid, the attitude stability domain is modified significantly in comparison with the classical stability domain predicted by the Beletskii–DeBra–Delp method on a circular orbit in a central gravity field. Especially, when the spacecraft is located on the intermediate-moment principal axis of the asteroid, the stability domain can be totally different from the classical stability domain. Our results are useful for the design of attitude control system in the future asteroid missions. 相似文献
20.
R. Chaubey 《Astrophysics and Space Science》2009,321(3-4):241-246
The Bianchi type-V universe filled with dark energy from a wet dark fluid has been considered. A new equation of state for the dark energy component of the universe has been used. It is modeled on the equation of state p=γ(ρ?ρ ? ) which can describe a liquid, for example water. The exact solutions to the corresponding field equations are obtained in quadrature form. The solution for constant deceleration parameter have been studied in detail for power-law and exponential forms both. The case $\gamma =\frac{1}{3}$ has been also analysed. 相似文献