2,726 research outputs found
Singular sources in the Demianski-Newman spacetimes
The analysis of singular regions in the NUT solutions carried out in the
recent paper (Manko and Ruiz, 2005 Class. Quantum Grav. 22, p.3555) is now
extended to the Demianski-Newman vacuum and electrovacuum spacetimes. We show
that the effect which produces the NUT parameter in a more general situation
remains essentially the same as in the purely NUT solutions: it introduces the
semi-infinite singularities of infinite angular momenta and positive or
negative masses depending on the interrelations between the parameters; the
presence of the electromagnetic field additionally endows the singularities
with electric and magnetic charges. The exact formulae describing the mass,
charges and angular momentum distributions in the Demianski-Newman solutions
are obtained and concise general expressions P_n=(m+i\nu)(ia)^n,
Q_n=(q+ib)(ia)^n for the entire set of the respective Beig-Simon multipole
moments are derived. These moments correspond to a unique choice of the
integration constant in the expression of the metric function \omega which is
different from the original choice made by Demianski and Newman.Comment: 22 pages, 5 figures; submitted to Classical and Quantum Gravit
How can exact and approximate solutions of Einstein's field equations be compared?
The problem of comparison of the stationary axisymmetric vacuum solutions
obtained within the framework of exact and approximate approaches for the
description of the same general relativistic systems is considered. We suggest
two ways of carrying out such comparison: (i) through the calculation of the
Ernst complex potential associated with the approximate solution whose form on
the symmetry axis is subsequently used for the identification of the exact
solution possessing the same multipole structure, and (ii) the generation of
approximate solutions from exact ones by expanding the latter in series of
powers of a small parameter. The central result of our paper is the derivation
of the correct approximate analogues of the double-Kerr solution possessing the
physically meaningful equilibrium configurations. We also show that the
interpretation of an approximate solution originally attributed to it on the
basis of some general physical suppositions may not coincide with its true
nature established with the aid of a more accurate technique.Comment: 32 pages, 5 figure
Classical gravitational spin-spin interaction
I obtain an exact, axially symmetric, stationary solution of Einstein's
equations for two massless spinning particles. The term representing the
spin-spin interaction agrees with recently published approximate work. The
spin-spin force appears to be proportional to the inverse fourth power of the
coordinate distance between the particles.Comment: six pages, no figures, journal ref:accepted for Classical and Quantum
Gravit
Approaches to the Monopole-Dynamic Dipole Vacuum Solution Concerning the Structure of its Ernst's Potential on the Symmetry Axis
The FHP algorithm allows to obtain the relativistic multipole moments of a
vacuum stationary axisymmetric solution in terms of coefficients which appear
in the expansion of its Ernst's potential on the symmetry axis. First of all,
we will use this result in order to determine, at a certain approximation
degree, the Ernst's potential on the symmetry axis of the metric whose only
multipole moments are mass and angular momentum.
By using Sibgatullin's method we analyse a series of exacts solutions with
the afore mentioned multipole characteristic. Besides, we present an
approximate solution whose Ernst's potential is introduced as a power series of
a dimensionless parameter. The calculation of its multipole moments allows us
to understand the existing differences between both approximations to the
proposed pure multipole solution.Comment: 24 pages, plain TeX. To be published in General Relativity and
Gravitatio
Extending Sibgatullin's ansatz for the Ernst potential to generate a richer family of axially symmetric solutions of Einstein's equations
The scope of this talk is to present some preliminary results on an effort,
currently in progress, to generate an exact solution of Einstein's equation,
suitable for describing spacetime around a rotating compact object.
Specifically, the form of the Ernst potential on the symmetry axis and its
connection with the multipole moments is discussed thoroughly. The way to
calculate the multipole moments of spacetime directly from the value of the
Ernst potential on the symmetry axis is presented. Finally, a mixed ansatz is
formed for the Ernst potential including parameters additional to the ones
dictated by Sibgatullin. Thus, we believe that this talk can also serve as a
comment on choosing the appropriate ansatz for the Ernst potential.Comment: Talk given in the 11th Conference on Recent Developments in Gravity,
2-5 June 2004, Lesbos, Greec
Equatorial symmetry/antisymmetry of stationary axisymmetric electrovac spacetimes
Two theorems are proved concerning how stationary axisymmetric electrovac
spacetimes that are equatorially symmetric or equatorially antisymmetric can be
characterized correctly in terms of the Ernst potentials \E and or in
terms of axis-data.Comment: 8 page
Quantum Limits in Interferometric GW Antennas
We discuss a model for interferometric GW antennas illuminated by a laser beam and a vacuum squeezed field. The sensitivity of the antenna will depend on the properties of the radiation entering the two ports and on the optical characteristics of the interferometer components, e.g. mirrors, beam-splitter, lenses
A continuation of a program of high angular resolution studies of celestial X-ray sources Final report, 19 Feb. - 1 Aug. 1968
Refurbishment and reflight of instrumented payload on Aerobee rocket for X ray astronomy progra
Analytical approximation of the exterior gravitational field of rotating neutron stars
It is known that B\"acklund transformations can be used to generate
stationary axisymmetric solutions of Einstein's vacuum field equations with any
number of constants. We will use this class of exact solutions to describe the
exterior vacuum region of numerically calculated neutron stars. Therefore we
study how an Ernst potential given on the rotation axis and containing an
arbitrary number of constants can be used to determine the metric everywhere.
Then we review two methods to determine those constants from a numerically
calculated solution. Finally, we compare the metric and physical properties of
our analytic solution with the numerical data and find excellent agreement even
for a small number of parameters.Comment: 9 pages, 10 figures, 3 table
Bounds on the force between black holes
We treat the problem of N interacting, axisymmetric black holes and obtain
two relations among physical parameters of the system including the force
between the black holes. The first relation involves the total mass, the
angular momenta, the distances and the forces between the black holes. The
second one relates the angular momentum and area of each black hole with the
forces acting on it.Comment: 13 pages, no figure
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