排序方式: 共有59条查询结果,搜索用时 18 毫秒
21.
We propose a new model of a gravastar admitting conformal motion. While retaining the framework of the Mazur-Mottola model, the gravastar is assumed to be internally charged, with an exterior defined by a Reissner-Nordström instead of a Schwarzschild line element. The solutions, obtained by exploiting an assumed conformal Killing vector, involve (i) the interior region, (ii) the shell, and (iii) the exterior region of the sphere. Of these three cases the first one is of primary interest since the total gravitational mass here turns out to be an electromagnetic mass under some specific conditions. This suggests that the interior de Sitter vacuum of a charged gravastar is essentially an electromagnetic mass model that must generate gravitational mass which provides a stable configuration by balancing the repulsive pressure arising from charge with its attractive gravity to avert a singularity. Therefore the present model, like the Mazur-Mottola model, results in the construction of a compact astrophysical object, as an alternative to a black hole. We have also analyzed various other aspects such as the stress energy tensor in the thin shell and the entropy of the system. 相似文献
22.
Stefan Baessler Mathieu Beau Michael Kreuz Vladimir N. Kurlov Valery V. Nesvizhevsky Guillaume Pignol Konstantin V. Protasov Francis Vezzu Aleksey Yu. Voronin 《Comptes Rendus Physique》2011,12(8):707-728
The existence of quantum states of matter in a gravitational field was demonstrated recently in the Institut Laue–Langevin (ILL), Grenoble, in a series of experiments with ultra cold neutrons (UCN). UCN in low quantum states is an excellent probe for fundamental physics, in particular for constraining extra short-range forces; as well as a tool in quantum optics and surface physics. The GRANIT is a follow-up project based on a second-generation spectrometer with ultra-high energy resolution, permanently installed in ILL. It has been constructed in framework of an ANR grant; and will become operational in 2011. 相似文献
23.
Priv.‐Doz. Dr. Alban Kellerbauer 《Physik in unserer Zeit》2012,43(4):174-180
24.
A. Giazotto 《Physics letters. A》2012,376(5):667-670
The working principles of a new kind of accelerometer that allows tilt angle to be measured separately from linear acceleration are presented here. This device could have relevant applications for creating inertial platforms and where an inertial suspension for test masses is needed, as it is the case of interferometric gravitational wave detectors. 相似文献
25.
Thorne and Kidder give expressions which allow for analytical estimates of the “kick”, i.e. the recoil, produced from asymmetrical
gravitational radiation during the interaction of black holes, or in fact any gravitating compact bodies. (The Thorne-Kidder
formula uses momentum flux calculations based on the linearized General Relativity of gravitational radiation). We specifically
treat kicks arising in the binary interaction of equal mass black holes, when at least one of the black holes has significant
spin, a. Such configurations can produce very large kicks in computational simulations. We consider both fly-by and quasicircular orbits. For fly-by orbits we find substantial kicks from those Thorne-Kidder terms which are linear in a. For the quasi-circular case, we consider in addition the nonlinear contribution (O(a
2)) to the kicks, and provide a dynamical explanation for such terms discovered and displayed by [2]. However, in the cases
of maximal kick velocities, the dependence on spin is largely linear (reproduced in numerical results [6]). 相似文献
26.
The recently developed mean field theory of relativistic gravitation predicts the emergence of an “apparent matter” field at large scales describing the net effect of small-scale fluctuations on the large-scale dynamics of the universe. It is found that this so-called back reaction effect is much stronger for gravitational waves than for matter density fluctuations. At large scales, gravitational waves behave like radiation and, for them, the perturbative effect scales as the squared relative amplitude times squared frequency. In particular, a bath of gravitational waves of relative amplitude 10−5 and frequency would not be directly detectable by today’s technology but would generate an effective large-scale radiation of amplitude comparable to the unperturbed matter density of the universe. 相似文献
27.
Evans attempted to develop a classical unified field theory of gravitation and electromagnetism on the background of a spacetime
obeying a Riemann-Cartan geometry. In an accompanying paper I, we analyzed this theory and summarized it in nine equations.
We now propose a variational principle for a theory that implements some of the ideas that have been (imprecisely) indicated
by Evans and show that it yields two field equations. The second field equation is algebraic in the torsion and we can resolve
it with respect to the torsion. It turns out that for all physical cases the torsion vanishes and the first field equation,
together with Evans’ unified field theory, collapses to an ordinary Einstein equation. 相似文献
28.
We consider the astrophysical and cosmological implications of the existence of a minimum density and mass due to the presence
of the cosmological constant. If there is a minimum length in nature, then there is an absolute minimum mass corresponding
to a hypothetical particle with radius of the order of the Planck length. On the other hand, quantum mechanical considerations
suggest a different minimum mass. These particles associated with the dark energy can be interpreted as the “quanta” of the
cosmological constant. We study the possibility that these particles can form stable stellar-type configurations through gravitational
condensation, and their Jeans and Chandrasekhar masses are estimated. From the requirement of the energetic stability of the
minimum density configuration on a macroscopic scale one obtains a mass of the order of 1055 g, of the same order of magnitude as the mass of the universe. This mass can also be interpreted as the Jeans mass of the
dark energy fluid. Furthermore we present a representation of the cosmological constant and of the total mass of the universe
in terms of ‘classical’ fundamental constants. 相似文献
29.
We set constraints and an upper bound on the masses required for a configuration of n point lenses to produce the maximum of 5n − 5 images of a distant source. We show how this result can be used to detect and constrain the mass of planets or brown
dwarfs in multiple-star systems. 相似文献
30.
Experimental verification of the existence of gravimagnetic fields generated by currents of matter is important for a complete
understanding and formulation of gravitational physics. Although the rotational (intrinsic) gravimagnetic field has been extensively studied and is now being measured by the Gravity Probe B, the extrinsic gravimagnetic field generated by the translational current of matter is less well studied. The present paper uses the post-Newtonian
parametrized Einstein and light geodesics equations to show that the extrinsic gravimagnetic field generated by the translational current of matter can be measured by observing the relativistic time delay
and/or light deflection caused by the moving mass. We prove that the extrinsic gravimagnetic field is generated by the relativistic effect of the aberration of the gravity force caused by the Lorentz
transformation of the metric tensor and the Levi–Civita connection. We show that the Lorentz transformation of the gravity
field variables is equivalent to the technique of the retarded Lienard–Wiechert gravitational potentials predicting that a
light particle is deflected by gravitational field of a moving body from its retarded position so that both general-relativistic
phenomena—the aberration and the retardation of gravity—are tightly connected and observing the aberration of gravity proves
that gravity has a causal nature. We explain in this framework the 2002 deflection experiment of a quasar by Jupiter where
the aberration of gravity from its orbital motion was measured with accuracy 20%. We describe a theory of VLBI experiment
to measure the gravitational deflection of radio waves from a quasar by the Sun, as viewed by a moving observer from the geocentric
frame, to improve the measurement accuracy of the aberration of gravity to a few percent. 相似文献