135 research outputs found
Search For Gravitational Waves Through the Electromagnetic Faraday Rotation
A method is given which renders indirect detection of strong gravitational
waves possible. This is based on the reflection (collision) of a linearly
polarized electromagnetic shock wave from (with) a cross polarized impulsive
and shock gravitational waves in accordance with the general theory of
relativity. This highly non-linear process induces a detectable Faraday
rotation in the polarization vector of the electromagnetic field.Comment: Final version. Minor revision, new figures and references are added.
To appear in Physical Review
Reflection of electromagnetic waves from mixtures of plane gravitational and scalar waves
We consider colliding wave packets consisting of hybrid mixtures of
electromagnetic, gravitational and scalar waves. Irrespective of the scalar
field, the electromagnetic wave still reflects from the gravitational wave.
Some reflection processes are given for different choice of packets in which
the Coulomb-like component vanishes. Exact solution for multiple
reflection of an electromagnetic wave from successive impulsive gravitational
waves is obtained in a closed form. It is shown that a succesive sign flip in
the Maxwell spinor arises as a result of encountering with an impulsive train
(i.e. the Dirac's comb curvature) of gravitational waves. Such an observable
effect may be helpful in the detection of gravitational wave bursts.Comment: 20 pages, 3 ps figures, small typos corrected, published versio
The centrifugal force reversal and X-ray bursts
Heyl (2000) made an interesting suggestion that the observed shifts in QPO
frequency in type I X-ray bursts could be influenced by the same geometrical
effect of strong gravity as the one that causes centrifugal force reversal
discovered by Abramowicz and Lasota (1974). However, his main result contains a
sign error. Here we derive the correct formula and conclude that constraints on
the M(R) relation for neutron stars deduced from the rotational-modulation
model of QPO frequency shifts are of no practical interest because the correct
formula implies a weak condition R* > 1.3 Rs, where Rs is the Schwarzschild
radius. We also argue against the relevance of the rotational-modulation model
to the observed frequency modulations.Comment: 3 pages, Minor revisions, A&A Letters, in pres
Back Reaction of Hawking Radiation on Black Hole Geometry
We propose a model for the geometry of a dynamical spherical shell in which
the metric is asymptotically Schwarzschild, but deviates from Ricci-flatness in
a finite neighbourhood of the shell. Hence, the geometry corresponds to a
`hairy' black hole, with the hair originating on the shell. The metric is
regular for an infalling shell, but it bifurcates, leading to two disconnected
Schwarzschild-like spacetime geometries. The shell is interpreted as either
collapsing matter or as Hawking radiation, depending on whether or not the
shell is infalling or outgoing. In this model, the Hawking radiation results
from tunnelling between the two geometries. Using this model, the back reaction
correction from Hawking radiation is calculated.Comment: Latex file, 15 pages, 4 figures enclosed, uses eps
No-go theorem for false vacuum black holes
We study the possibility of non-singular black hole solutions in the theory
of general relativity coupled to a non-linear scalar field with a positive
potential possessing two minima: a `false vacuum' with positive energy and a
`true vacuum' with zero energy. Assuming that the scalar field starts at the
false vacuum at the origin and comes to the true vacuum at spatial infinity, we
prove a no-go theorem by extending a no-hair theorem to the black hole
interior: no smooth solutions exist which interpolate between the local de
Sitter solution near the origin and the asymptotic Schwarzschild solution
through a regular event horizon or several horizons.Comment: 16 pages, 1 figure, Latex, some references added, to appear in
Classical and Quantum Gravit
On critical behaviour in gravitational collapse
We give an approach to studying the critical behaviour that has been observed
in numerical studies of gravitational collapse. These studies suggest, among
other things, that black holes initially form with infinitesimal mass. We show
generally how a black hole mass formula can be extracted from a transcendental
equation.
Using our approach, we give an explicit one parameter set of metrics that are
asymptotically flat and describe the collapse of apriori unspecified but
physical matter fields. The black hole mass formula obtained from this metric
exhibits a mass gap - that is, at the onset of black hole formation, the mass
is finite and non-zero.Comment: 11 pages, RevTex, 2 figures (available from VH
Pair of null gravitating shells I. Space of solutions and its symmetries
The dynamical system constituted by two spherically symmetric thin shells and
their own gravitational field is studied. The shells can be distinguished from
each other, and they can intersect. At each intersection, they exchange energy
on the Dray, 't Hooft and Redmount formula. There are bound states: if the
shells intersect, one, or both, external shells can be bound in the field of
internal shells. The space of all solutions to classical dynamical equations
has six components; each has the trivial topology but a non trivial boundary.
Points within each component are labeled by four parameters. Three of the
parameters determine the geometry of the corresponding solution spacetime and
shell trajectories and the fourth describes the position of the system with
respect to an observer frame. An account of symmetries associated with
spacetime diffeomorphisms is given. The group is generated by an infinitesimal
time shift, an infinitesimal dilatation and a time reversal.Comment: 28 pages, 9 figure included in the text, Latex file using amstex,
epic and graphi
Self-gravitating fluid shells and their non-spherical oscillations in Newtonian theory
We summarize the general formalism describing surface flows in
three-dimensional space in a form which is suitable for various astrophysical
applications. We then apply the formalism to the analysis of non-radial
perturbations of self-gravitating spherical fluid shells.
Spherically symmetric gravitating shells (or bubbles) have been used in
numerous model problems especially in general relativity and cosmology. A
radially oscillating shell was recently suggested as a model for a variable
cosmic object. Within Newtonian gravity we show that self-gravitating static
fluid shells are unstable with respect to linear non-radial perturbations. Only
shells (bubbles) with a negative mass (or with a charge the repulsion of which
is compensated by a tension) are stable.Comment: 20 pages, to be published in the Astrophysical Journal, typos
correcte
Geometry of Deformations of Relativistic Membranes
A kinematical description of infinitesimal deformations of the worldsheet
spanned in spacetime by a relativistic membrane is presented. This provides a
framework for obtaining both the classical equations of motion and the
equations describing infinitesimal deformations about solutions of these
equations when the action describing the dynamics of this membrane is
constructed using {\it any} local geometrical worldsheet scalars. As examples,
we consider a Nambu membrane, and an action quadratic in the extrinsic
curvature of the worldsheet.Comment: 20 pages, Plain Tex, sign errors corrected, many new references
added. To appear in Physical Review
Gravitational collapse of Type II fluid in higher dimensional space-times
We find the general solution of the Einstein equation for spherically
symmetric collapse of Type II fluid (null strange quark fluid) in higher
dimensions. It turns out that the nakedness and curvature strength of the shell
focusing singularities carry over to higher dimensions. However, there is
shrinkage of the initial data space for a naked singularity of the Vaidya
collapse due to the presence of strange quark matter.Comment: RevTex4 style, 4 pages; Accepted in Phys. Rev.
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