共查询到20条相似文献，搜索用时 15 毫秒
1.
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
2.
Uwe Kasper 《Astronomische Nachrichten》1972,294(5):201-206
In the framework of TREDER 's gravitational theory we elaborate the consequences of a class of field equations for some solar-system effects and their connection to the problem of cosmological singularity. These equations read on special conditions with components of the energy momentum tensor, KRONECKER 's symbol, tetrad components). ω is a real parameter. If we choose the integration constants of the static spherically symmetric vacuum case in such a way that red shift is the same like that of EINSTEIN 's theory and the source of gravitational field is that of a point mass we obtain for the perihelion rotation the expression is EINSTEINS value of the perihelion rotation.) For we obtain But only if ω > 2/5 cosmological models exist which have no cosmological singularity. On the other hand for ω > 2/5 the value is greater than. 相似文献
3.
Ioannis Gkigkitzis Ioannis Haranas Samantha Kirk 《Astrophysics and Space Science》2013,346(2):553-557
In this study, we have investigated the geometrical and physical properties of stationary axisymmetric solutions. The expressions for the axial-vector and the gravitational energy and momentum densities are obtained in the context of teleparallel equivalent of general relativity. The obtained results are compared with that obtained previously in the context of Møller’s tetrad theory of gravitation. We discussed special cases of these solutions. 相似文献
4.
Gamal G. L. Nashed 《Astrophysics and Space Science》2011,335(2):593-598
We give a class of spherically symmetric-Anti de Sitter (Ads), exact solution in the teleparallel equivalent of general relativity
(TEGR). The solution depends on an arbitrary function F(R)\mathcal{F}(R) and reproduce the metric of Schwarzschild Ads space-time. In the context of the Hamiltonian formulation of the TEGR we compute
the gravitational energy of this class. The calculation is carried out by means of an expression for the energy of the gravitational
field that naturally arises from the integral form of the constraint equations of the formalism. We show that the form of
the energy depends on the arbitrary function. We make a constrain on this arbitrary function to give the correct form of energy. 相似文献
5.
Motoyuki Saijo † Shin'ichirou Yoshida ‡ 《Monthly notices of the Royal Astronomical Society》2006,368(3):1429-1442
We study the nature of non-axisymmetric dynamical instabilities in differentially rotating stars with both linear eigenmode analysis and hydrodynamic simulations in Newtonian gravity. We especially investigate the following three types of instability; the one-armed spiral instability, the low T /| W | bar instability, and the high T /| W | bar instability, where T is the rotational kinetic energy and W is the gravitational potential energy. The nature of the dynamical instabilities is clarified by using a canonical angular momentum as a diagnostic. We find that the one-armed spiral and the low T /| W | bar instabilities occur around the corotation radius, and they grow through the inflow of canonical angular momentum around the corotation radius. The result is a clear contrast to that of a classical dynamical bar instability in high T /| W | . We also discuss the feature of gravitational waves generated from these three types of instability. 相似文献
6.
Gamal G. L. Nashed 《Astrophysics and Space Science》2013,348(2):591-598
A general tetrad fields, with an arbitrary function of radial coordinate, preserving spherical symmetry, is provided. Such tetrad is split into two matrices: The first matrix represents a Local Lorentz Transformation (LLT), which contains an arbitrary function. The second matrix represents a proper tetrad fields which satisfy the field equations of f(T) gravitational theory. This general tetrad is applied to the field equations of f(T). We derive a solution with one constant of integration to the resulting field equations of f(T). This solution gives a vanishing value of the scalar torsion. We calculate the energy associated with this solution to investigate what is the nature of the constant of integration. 相似文献
7.
The gravitational collapse of molecular clouds or cloud cores is expected to lead to the formation of stars that begin their lives in a state of rapid rotation. It is known that, in at least some specific cases, rapidly rotating, slf-gravitating bodies are subject to instabilities that cause them to assume ellipsoidal shapes. In this paper we investigate the consequences of such instabilities on the angular momentum evolution of a star in the process of formation from a collapsing cloud, and surrounded by a protostellar disk, with a view toward applications to the formation of the Solar System. We use a specific model of star formation to demonstrate the possibility that such a star would become unstable, that the resulting distortion of the star would generate spiral density waves in the circumstellar disk, and that the torque associated with these waves would regulate the angular momentum of the star as it feeds angular momentum to the disk. We conclude that the angular momentum so transported to the disk would not spread the disk to, say, Solar System dimensions, by the action of the spiral density waves alone. However, a viscous disk could effectively extract stellar angular momentum and attain Solar System size. Our results also indicate that viscous disks could feed mass and angular momentum to a growing protostar in such a manner that distortions of the star would occur before gravitational torques could balance the influx of angular momentum. In other situations (in which the viscosity was small), a gap could be cleared between the disk and star. 相似文献
8.
We consider macroscopic flow of energy and momentum between the solar wind and outer magnetosphere. We point out that using the integral form of magnetohydrodynamic equations is more natural than the differential form for consideration of energy and momentum flows and should yield more accurate results from magnetic field data. We use the notation of general relativity because it is straightforward and brief. 相似文献
9.
Ernst Fischer 《Astrophysics and Space Science》1992,190(1):149-153
Applying the basic concepts of general relativity to the global motion of a particle in a mass-filled universe leads to a loss of momentum relative to the rest frame of the Universe. This loss is caused by the different running times of the gravitational interaction quanta exchanged with masses in front and behind the moving particle, if the signal velocity is limited to the speed of light. Due to this gravitational viscosity of space, the energy of photons will be reduced with the time, and thus with the distance of the emitting source. This red shift is superimposed on the Doppler shift in an expanding universe. A discussion of the limiting case of vanishing expansion leads to predictions about mass and radius of the Universe. The value of the mass density in such a steady-state universe must be about three times the closing density discussed in Big-Bang theories. The existence of the gravitational viscosity casts severe doubts on all estimations of the age of the Universe derived from the red-shift data. 相似文献
10.
11.
Tetsuya Tokano 《Planetary and Space Science》2010,58(5):814-829
The orientation of the atmospheric angular momentum vector of Titan and its temporal variation predicted by a general circulation model are analysed and interpreted. The atmospheric angular momentum vector is tilted by a few degrees from the polar axis and the vector rotates (precesses) westward with a constant period of 1 Titan day. The fast westward rotation is likely to be caused by migrating diurnal thermal tides. The tilt is almost cancelled out in the troposphere by the wavenumber 2 pattern of Saturn's gravitational tide, but is more pronounced in the stratosphere, where thermal tides are significant. The predicted tilt angle and the equatorial angular momentum vary with season and maximize when the hemispheric asymmetry of the axial angular momentum or superrotation attains its peak. 相似文献
12.
Paul S. Wesson 《Earth, Moon, and Planets》1984,30(3):275-280
Protostars in a group exert gravitational tidal torques on an aspherical nebula located in the group. The net torque transfers angular momentum from the orbital motions of the stars to rotation of the nebula. A relation can be derived between the parameters describing the protostars and the final angular momentum of the nebula. While the parameters concerned are uncertain, a conservative choice results in a value for the angular momentum equal to about 1/3 of that of the present solar system. This suggests that if the Sun formed in a group, tidal interactions with other protostars may account for a significant part of the angular momentum of the solar system. 相似文献
13.
Adri��n Rodr��guez Tatiana A. Michtchenko Octavio Miloni 《Celestial Mechanics and Dynamical Astronomy》2011,111(1-2):161-178
We investigate the secular dynamics of two-planet coplanar systems evolving under mutual gravitational interactions and dissipative forces. We consider two mechanisms responsible for the planetary migration: star-planet (or planet-satellite) tidal interactions and interactions of a planet with a gaseous disc. We show that each migration mechanism is characterized by a specific law of orbital angular momentum exchange. Calculating stationary solutions of the conservative secular problem and taking into account the orbital angular momentum leakage, we trace the evolutionary routes followed by the planet pairs during the migration process. This procedure allows us to recover the dynamical history of two-planet systems and constrain parameters of the involved physical processes. 相似文献
14.
We present a general parametrization for the leading order terms in a momentum power expansion of a non-universal Lorentz-violating, but rotational invariant, kinematics and its implications for two-body decay thresholds. The considered framework includes not only modified dispersion relations for particles, but also modified energy–momentum conservation laws, something which goes beyond effective field theory. As a particular and relevant example, bounds on the departures from special relativistic kinematics from the non-observation of vacuum Cherenkov radiation are discussed and compared with those obtained within the effective field theory scenario. 相似文献
15.
A non-static exact solution of the Einstein equations corresponding to a conformally invariant scalar field with trace-free energy momentum tensor is obtained for the Robertson-Walker type metric. Some physical properties of the solution are discussed. 相似文献
16.
We investigate the feasibility of using the Lense-Thirring effect to measure the rotational angular momentum of Jupiter and the Sun. This experiment uses gyroscopes in close Jovian and solar orbits. It is important because it provides direct, unique information. The angular momentum is not derivable from the gravitational moments when non-uniform rotation is present. Analysis shows that this experiment could be done around Jupiter with current technology, but could not be done around the Sun for some years.Supported in part, by a Dissertation Research Assistantship of the Graduate College, Iowa State University. 相似文献
17.
S. K. Tripathy S. K. Nayak S. K. Sahu T. R. Routray 《Astrophysics and Space Science》2009,323(1):91-96
Bianchi type-I string cosmological models are studied in Saez-Ballester theory of gravitation when the source for the energy
momentum tensor is a viscous string cloud coupled to gravitational field. The bulk viscosity is assumed to vary with time
and is related to the scalar expansion. The relationship between the proper energy density ρ and string tension density λ are investigated from two different cosmological models. 相似文献
18.
Farook Rahaman 《Astrophysics and Space Science》2002,280(4):337-343
We present an approximate solution of global monopole based on Lyra geometry retaining terms of the order 1/3
2 in the energy momentum tensor for a triplet scalar field. Also the gravitational field of the monopole solution has been
considered.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
Roland Sergysels 《Celestial Mechanics and Dynamical Astronomy》1988,44(1-2):155-166
As is well known, the orbital and rotational motions of a solid are coupled, and the integrals of energy and angular momentum (in a gravitational field with spherical symmetry) impose restrictions on them. We study the regions allowed to the motion in configurational space. It turns out that even in the crudest model (planar motion of a triple rod) the restrictions on the libration angle and the orbital radius of the center of mass are coupled, so that excessive ellipticity of the orbit excludes stabilization in the neighbourhood of the spoke equilibrium position by gravitational forces only.Chargé de Cours. 相似文献
20.