共查询到20条相似文献，搜索用时 15 毫秒
1.
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.
2.
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
3.
T. Padmanabhan 《Astrophysics and Space Science》2003,285(2):407-417
The Einstein-Hilbert action (and thus the dynamics of gravity) can be obtained by: (i) combining the principle of equivalence, special relativity and quantum theory in the Rindler frame and (ii) postulating that the horizon area must be proportional to the entropy. This approach uses the local Rindler frame as a natural extension of the local inertial frame, and leads to the interpretation that the gravitational action represents the free energy of the spacetime geometry. As an aside, one obtains an insight into the peculiar structure of Einstein-Hilbert action and a natural explanation to the questions: (i) Why does the covariant action for gravity contain second derivatives of the metric tensor? (ii) Why is the gravitational coupling constant positive? Some geometrical features of gravitational action are clarified. 相似文献
4.
David F. Roscoe 《Astrophysics and Space Science》1995,227(1-2):119-132
It is shown that global four-momentum conservation provides all the necessary structure toderive a metric gravity theory which conforms to the requirements of the Strong Equivalence Principle (Will, 1981), and which satisfies all empirical tests up to, and including, those derived from the binary pulsar measurements. Significant consequences arising from this theory are: concepts of curved spacetimes become strictly superfluous to the function of describing gravitational physics; gravitational processes become direct particle/particle interactions; these interactions are arbitrated by wave processes of a kind familiar in electromagnetism; gravitational waves carry energy-momentum in the direction of their propogation vector; the essential singularities at gravitational origins, which are features of both Newtonian gravitation and General Relativity, do not exist. 相似文献
5.
We describe the departure from equilibrium of matter distributions representing sources for a class of Weyl metric. It is
shown that, for extremely high gravitational fields, slight deviations from spherical symmetry may weaken its tendency to
a catastrophic collapse. For critical values of surface gravitational potential, in contrast with the exactly spherically
symmetric case, the speed of entering the collapse regime decreases substantially, at least for specific cases.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
The stability of a recently proposed general relativistic model of galaxies is studied in some detail. This model is a general relativistic version of the well-known Miyamoto–Nagai model that represents well a thick galactic disc. The stability of the disc is investigated under a general first-order perturbation keeping the space–time metric frozen (no gravitational radiation is taken into account). We find that the stability is associated with the thickness of the disc. We find that flat galaxies have more non-stable modes than the thick ones, i.e. flat galaxies have a tendency to form more complex structures like rings, bars and spiral arms. 相似文献
7.
This paper presents a scalar-tensor theory of gravitation with a flat background metric and an arbitrary coupling function. In what concerns PPN approximation as well as the speed and polarization of the weak gravitational wave, the suggested theory coincides with GR, while in the case of the strong field of gravitation it may considerably differ from GR. 相似文献
8.
A solution of linearized Einstein field equations in vacuum is given and discussed. First it is shown that, computing from our particular metric the linearized connections, the linearized Riemann tensor and the linearized Ricci tensor, the linearized Ricci tensor results equal to zero. Then the effect on test masses of our solution, which is a gravitational wave, is discussed. In our solution test masses have an apparent motion in the direction of propagation of the wave, while in the transverse direction they appear at rest. In this way it is possible to think that gravitational waves would be longitudinal waves, but, from careful investigation of this solution, it is shown that the tidal forces associated with gravitational waves act along the directions orthogonal to the direction of propagation of waves. The computation is first made in the long wavelengths approximation (wavelength much larger than the linear distances between test masses), then the analysis is generalized to all gravitational waves.
In the last sections of this paper it is shown that the frequency dependent angular pattern of interferometers can be obtained from our solution and the total signal seen from an interferometer for the stochastic background of gravitational waves is computed. 相似文献
9.
Few years ago, Cho and Vilenkin have proposed that topological defects can arise in symmetry breaking models without having degenerate vacua. These types of defects are known as vacuumless defects. In the present work, the gravitational field of a vacuumless global string and global monopole have been investigated in the context of Lyra geometry. We find the metric of the vacuumless global string and global monopole in the weak field approximations. It has been shown that the vacuumless global string can have repulsive whereas global monopole exerts attractive gravitational effects on a test particle. It is dissimilar to the case studied in general relativity. 相似文献
10.
Wang Yong-jiu 《Chinese Astronomy and Astrophysics》1984,8(4):283-285
In this paper, a metric containing five arbitrary functions of time is obtained which describes the gravitational field of an arbitrary accelerated and charged point-mass (star). It is a further generalization of Vaidya's star metric, [1]. In particular cases, it reduces to the Reissner-Nortström metric and the Kinnersley metric [2]. Since the various parameters of the source can vary arbitrarily in time, this metric is of wide applicability and may prove to be useful for various specific astronomical objects. 相似文献
11.
The problem of semiclassical gravitational effects of globalmonopole in Kalb-Ramond backgroundinvestigated. It is shown that the monopoleexerts repulsive gravitational force on nonrelativistic matter and space around it hasa deficit solid angle. 相似文献
12.
The equation of motion written down using a metric obtained from the Kerr metric allows us to get both the deflection angle of light ray bending by the gravitational field of the Sun and its corresponding time delay. We reproduce the experimental data of Epstein-Shapiro and also it is in accordance with the theoretical results obtained by Brumberget al. (1990) using another approach to this problem.Presented at the 2nd UN/ESA Workshop, held in Bogotá, Colombia, 9–13 November, 1992. 相似文献
13.
A theory of gravitation with a flat background metric and a dynamical variable (variable gravitational constant) is investigated. It is shown that such bimetric scalar-tensor theory (BSTT) generalized GR as all the solutions of GR equations and(x) = constant satisfy BSTT equations, firstly, and BSTT equations contain non-Einstein solutions with the variable, secondly. Due to this fact, the problem on the agreement of BSTT with the observational data is reduced to the problem on the agreement of GR with the observational data and to the interpretation of the solutions with the variable. The latter may prove useful for the prediction of new effects. Examples of such effects are discussed. 相似文献
14.
Paul S. Wesson 《Astrophysics and Space Science》1974,30(1):71-94
Algebraic conditions on the continuity of the components of the metric tensor are employed to get an approximate metric in four limiting forms relevant to a condensation in an expanding Einstein/de Sitter substratum. The metric of the condensation is in general spherically-symmetric, nonstatic and asymptotically flat, passing over into the usual Friedmann solution at large distances and late times. The line-element derived supersedes an earlier incorrect formulation of the problem by Einstein and Straus. The metric is applicable in particular to clusters of galaxies, wich cannot avoid being involved in the expansion of the Universe for the density-distributions relevant to average loose clusters as presently observed. It is likely that all clusters, including compact ones, are in a state of dynamical evolution, a conclusion which may remove the missing mass problem. The results found agree, in this respect, with recent work by Noerdlinger and Petrosian, and give effective Hubble parmeters for systems in an expanding substratum. 相似文献
15.
We analyze the behavior of the scalar field as dark energy of the Universe in a static world of galaxies and clusters of galaxies. We find the analytical solutions of evolution equations of the density and velocity perturbations of dark matter and dark energy, which interact only gravitationally, along with the perturbations of metric in a static world with background Minkowski metric. It was shown that quintessential and phantom dark energy in the static world of galaxies and clusters of galaxies is gravitationally stable and can only oscillate by the influence of self-gravity. In the gravitational field of dark matter perturbations, it is able to condense monotonically, but the amplitude of density and velocity perturbations on all scales remains small. It was also illustrated that the “accretion” of phantom dark energy in the region of dark matter overdensities causes formation of dark energy underdensities-the regions with negative amplitude of density perturbations of dark energy. 相似文献
16.
Walter Petry 《Astrophysics and Space Science》1991,175(1):1-14
The study of a previously proposed theory of gravitation in flat space-time (Petry, 1981a) is continued. A conservation law for the angular momentum is derived. Additional to the usual form, there must be added a term coming from the spin of the gravitational field. The equations of motion and of spin angular momentum for a spinning test particle in a gravitational field are given. An approximation of the equations of the spin angular momentum in the rest frame of the test particle is studied. For a gyroscope in an orbit of a rotating massive body (e.g., the Earth) the precession of the spin axis agrees with the result of Einstein's general theory of relativity. 相似文献
17.
Vacuum field equations for the static and non-static plane-symmetric metric are obtained in self-creation theory of gravitation proposed by Barber (1982). It is shown that, in both static and non-static cases, the only plane-symmetric solution in vacuum is the empty flat space-time of Einstein's theory. It is observed that this result is quite different from that of the Brans-Dicke and other scalar-tensor theories of gravitation. 相似文献
18.
It is shown that the Bekenstein-Hawking entropy of black holes can accept a correction that effects on the radiation tunneling probability. By assumption of a spatially flat universe accompanied with expansion of metric, we could obtain an expression for entropy of black hole that is changing with respect to time and Bekenstein-Hawking temperature. 相似文献
19.
M. V. Sazhin V. E. Zharov A. V. Volynkin & T. A. Kalinina 《Monthly notices of the Royal Astronomical Society》1998,300(1):287-291
The fluctuation of the angular positions of reference extragalactic radio and optical sources under the influence of the irregular gravitational field of visible Galactic stars is considered. It is shown that these angular fluctuations range from a few up to hundreds of microarcseconds. This leads to a small rotation of the celestial reference frame. The non-diagonal coefficients of the rotation matrix are of the order of a microarcsecond. The temporal variation of these coefficients due to the proper motion of the foreground stars is of the order of one microsecond per 20 years. The celestial reference frame can therefore be considered inertial and homogeneous only to microarcsecond accuracy. Astrometric catalogues with microarcsecond accuracy will be unstable, and must be re-established every 20 years. 相似文献
20.
N. Tomimura 《Astrophysics and Space Science》1993,201(2):223-228
The gravitational collapse of a slowly rotating star with small deviations from spherical symmetry is studied. The exterior metric is chosen to be the Kerr metric in synchronous coordinates discarding terms of order (a/r)2. Interior geometry is constructed by adding an off-diagonal term in first order ofa to the exact solution of the non-rotating case. This term is determined in part by requiring the validity of the junction conditions at the star's surface and by demanding that the angular momentum of the source is equal toM A, in agreement with the value measured by a distant observer. The resulting stress-energy tensor describes a homogeneous, pressureless, ideal fluid which rotates nonuniformly relative to the synchronous frame which is no longer comoving the stellar matter. 相似文献