357 research outputs found
Aichelburg-Sexl boost of an isolated source in general relativity
A study of the Aichelburg--Sexl boost of the Schwarzschild field is described
in which the emphasis is placed on the field (curvature tensor) with the metric
playing a secondary role. This is motivated by a description of the Coulomb
field of a charged particle viewed by an observer whose speed relative to the
charge approaches the speed of light. Our approach is exemplified by carrying
out an Aichelburg-- Sexl type boost on the Weyl vacuum gravitational field due
to an isolated axially symmetric source. Detailed calculations of the boosts
transverse and parallel to the symmetry axis are given and the results, which
differ significantly, are discussed.Comment: 25 pages, LateX2
Morgan-Morgan-NUT disk space via the Ehlers transformation
Using the Ehlers transformation along with the gravitoelectromagnetic
approach to stationary spacetimes we start from the Morgan-Morgan disk
spacetime (without radial pressure) as the seed metric and find its
corresponding stationary spacetime. As expected from the Ehlers transformation
the stationary spacetime obtained suffers from a NUT-type singularity and the
new parameter introduced in the stationary case could be interpreted as the
gravitomagnetic monopole charge (or the NUT factor). As a consequence of this
singularity there are closed timelike curves (CTCs) in the singular region of
the spacetime. Some of the properties of this spacetime including its particle
velocity distribution, gravitational redshift, stability and energy conditions
are discussed.Comment: 18 pages, 5 figures, RevTex 4, replaced with the published versio
Measuring multipole moments of Weyl metrics by means of gyroscopes
Using the technique of Rindler and Perlick we calculate the total precession
per revolution of a gyroscope circumventing the source of Weyl metrics. We
establish thereby a link between the multipole moments of the source and an
``observable'' quantity. Special attention deserves the case of the
gamma-metric. As an extension of this result we also present the corresponding
expressions for some stationary space-times.Comment: 18 pages Latex, To appear in J.Math.Phy
Exact relativistic models of thin disks around static black holes in a magnetic field
The exact superposition of a central static black hole with surrounding thin
disk in presence of a magnetic field is investigated. We consider two models of
disk, one of infinite extension based on a Kuzmin-Chazy-Curzon metric and other
finite based on the first Morgan-Morgan disk. We also analyze a simple model of
active galactic nuclei consisting of black hole, a Kuzmin-Chazy-Curzon disk and
two rods representing jets, in presence of magnetic field. To explain the
stability of the disks we consider the matter of the disk made of two
pressureless streams of counterrotating charged particles (counterrotating
model) moving along electrogeodesic. Using the Rayleigh criterion we derivate
for circular orbits the stability conditions of the particles of the streams.
The influence of the magnetic field on the matter properties of the disk and on
its stability are also analyzed.Comment: 17 pages, 14 figures. arXiv admin note: text overlap with
arXiv:gr-qc/0409109 by other author
Relativistic Static Thin Disks with Radial Stress Suport
New solutions for static non-rotating thin disks of finite radius with
nonzero radial stress are studied. A method to introduce either radial pressure
or radial tension is presented. The method is based on the use of conformal
transformations.Comment: 19 pages, LaTeX, 7 figures, submitted to Class. Quan. Gra
Relativistic Static Thin Disks: The Counter-Rotating Model
A detailed study of the Counter-Rotating Model (CRM) for generic finite
static axially symmetric thin disks with nonzero radial pressure is presented.
We find a general constraint over the counter-rotating tangential velocities
needed to cast the surface energy-momentum tensor of the disk as the
superposition of two counter-rotating perfect fluids. We also found expressions
for the energy density and pressure of the counter-rotating fluids. Then we
shown that, in general, there is not possible to take the two counter-rotating
fluids as circulating along geodesics neither take the two counter-rotating
tangential velocities as equal and opposite. An specific example is studied
where we obtain some CRM with well defined counter-rotating tangential
velocities and stable against radial perturbations. The CRM obtained are in
agree with the strong energy condition, but there are regions of the disks with
negative energy density, in violation of the weak energy condition.Comment: 19 pages, 6 figures. Submitted to Physical Review
Geodesics in a quasispherical spacetime: A case of gravitational repulsion
Geodesics are studied in one of the Weyl metrics, referred to as the M--Q
solution. First, arguments are provided, supporting our belief that this
space--time is the more suitable (among the known solutions of the Weyl family)
for discussing the properties of strong quasi--spherical gravitational fields.
Then, the behaviour of geodesics is compared with the spherically symmetric
situation, bringing out the sensitivity of the trajectories to deviations from
spherical symmetry. Particular attention deserves the change of sign in proper
radial acceleration of test particles moving radially along symmetry axis,
close to the surface, and related to the quadrupole moment of the
source.Comment: 30 pages late
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