47 research outputs found
Disk sources of the Kerr and Tomimatsu-Sato spacetimes: construction and physical properties
We construct the disk sources matched to the exact vacuum Kerr and to the two
classes of Tomimatsu-Sato spacetimes. We analyze two models of the matter
forming these disks. At each radius we consider either a rotating massive ring
with pressure or two counter-rotating streams of particles in circular geodesic
motion. Dragging effects present in such spacetimes lead either to rotation of
rings or asymmetry of both streams. We demonstrate that the model of rotating
rings is general enough to describe all axisymmetric stationary disk sources
with vanishing radial pressure which satisfy weak energy condition, and that
centrifugal effects present in the disk sources of spacetimes with large
angular momentum prevent the construction of highly compact sources made of
counter-rotating streams of geodesic particles. We illustrate the radial
distribution of the mass inside the disks and the angular velocities of both
geodesic streams
The fields of uniformly accelerated charges in de Sitter spacetime
The scalar and electromagnetic fields of charges uniformly accelerated in de
Sitter spacetime are constructed. They represent the generalization of the Born
solutions describing fields of two particles with hyperbolic motion in flat
spacetime. In the limit Lambda -> 0, the Born solutions are retrieved. Since in
the de Sitter universe the infinities I^+- are spacelike, the radiative
properties of the fields depend on the way in which a given point of I^+- is
approached. The fields must involve both retarded and advanced effects: Purely
retarded fields do not satisfy the constraints at the past infinity I^-.Comment: 5 pages, 3 figures, RevTeX; Slightly expanded version of the paper
published in Physical Review Letters. (The published version can be generated
from the same TeX source.); problem with the postscript fixe
Toroidal Perturbations of Friedmann-Robertson-Walker Universes
Explicit expressions are found for the axisymmetric metric perturbations of
the closed, flat and open FRW universes caused by toroidal motions of the
cosmic fluid. The perturbations are decomposed in vector spherical harmonics on
2-spheres, but the radial dependence is left general. Solutions for general
odd-parity -pole perturbations are given for either angular velocities or
angular momenta prescribed. In particular, in case of closed universes the
solutions require a special treatment of the Legendre equation.Comment: 13 page
The Newtonian limit of spacetimes for accelerated particles and black holes
Solutions of vacuum Einstein's field equations describing uniformly
accelerated particles or black holes belong to the class of boost-rotation
symmetric spacetimes. They are the only explicit solutions known which
represent moving finite objects. Their Newtonian limit is analyzed using the
Ehlers frame theory. Generic spacetimes with axial and boost symmetries are
first studied from the Newtonian perspective. The results are then illustrated
by specific examples such as C-metric, Bonnor-Swaminarayan solutions,
self-accelerating "dipole particles", and generalized boost-rotation symmetric
solutions describing freely falling particles in an external field. In contrast
to some previous discussions, our results are physically plausible in the sense
that the Newtonian limit corresponds to the fields of classical point masses
accelerated uniformly in classical mechanics. This corroborates the physical
significance of the boost-rotation symmetric spacetimes
Geodesics in spacetimes with expanding impulsive gravitational waves
We study geodesic motion in expanding spherical impulsive gravitational waves
propagating in a Minkowski background. Employing the continuous form of the
metric we find and examine a large family of geometrically preferred geodesics.
For the special class of axially symmetric spacetimes with the spherical
impulse generated by a snapping cosmic string we give a detailed physical
interpretation of the motion of test particles.Comment: 12 pages, Revtex, final versio