2,812 research outputs found
The double-Kerr equilibrium configurations involving one extreme object
We demonstrate the existence of equilibrium states in the limiting cases of
the double-Kerr solution when one of the constituents is an extreme object. In
the `extreme-subextreme' case the negative mass of one of the constituents is
required for the balance, whereas in the `extreme-superextreme' equilibrium
configurations both Kerr particles may have positive masses. We also show that
the well-known relation |J|=M^2 between the mass and angular momentum in the
extreme single Kerr solution ceases to be a characteristic property of the
extreme Kerr particle in a binary system.Comment: 12 pages, 3 figures, submitted to Class. Quantum Gra
Determining parameters of the Neugebauer family of vacuum spacetimes in terms of data specified on the symmetry axis
We express the complex potential E and the metrical fields omega and gamma of
all stationary axisymmetric vacuum spacetimes that result from the application
of two successive quadruple-Neugebauer (or two double-Harrison) transformations
to Minkowski space in terms of data specified on the symmetry axis, which are
in turn easily expressed in terms of multipole moments. Moreover, we suggest
how, in future papers, we shall apply our approach to do the same thing for
those vacuum solutions that arise from the application of more than two
successive transformations, and for those electrovac solutions that have axis
data similar to that of the vacuum solutions of the Neugebauer family.
(References revised following response from referee.)Comment: 18 pages (REVTEX
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
Fully Electrified Neugebauer Spacetimes
Generalizing a method presented in an earlier paper, we express the complex
potentials E and Phi of all stationary axisymmetric electrovac spacetimes that
correspond to axis data of the form E(z,0) = (U-W)/(U+W) , Phi(z,0) = V/(U+W) ,
where U = z^{2} + U_{1} z + U_{2} , V = V_{1} z + V_{2} , W = W_{1} z + W_{2} ,
in terms of the complex parameters U_{1}, V_{1}, W_{1}, U_{2}, V_{2} and W_{2},
that are directly associated with the various multipole moments. (Revised to
clarify certain subtle points.)Comment: 25 pages, REVTE
On interrelations between Sibgatullin's and Alekseev's approaches to the construction of exact solutions of the Einstein-Maxwell equations
The integral equations involved in Alekseev's "monodromy transform" technique
are shown to be simple combinations of Sibgatullin's integral equations and
normalizing conditions. An additional complex conjugation introduced by
Alekseev in the integrands makes his scheme mathematically inconsistent;
besides, in the electrovac case all Alekseev's principal value integrals
contain an intrinsic error which has never been identified before. We also
explain how operates a non-trivial double-step algorithm devised by Alekseev
for rewriting, by purely algebraic manipulations and in a different (more
complicated) parameter set, any particular specialization of the known
analytically extended N-soliton electrovac solution obtained in 1995 with the
aid of Sibgatullin's method.Comment: 7 pages, no figures, section II extende
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
Fabrication of a focusing soft X-ray collector payload
A large area X-ray focusing collector with arc minute resolution and a position sensitive detector capable of operating in the soft X-ray region was developed for use on sounding rockets in studying stellar X-ray sources. The focusing payload consists of the following components, which are described: (1) a crossed paraboloid mirror assembly; (2) an aspect camera and star tracker; (3) a focal plane assembly containing an imaging proportional counter and its preamplifiers, high voltage power supplies and gas system; (4) a fiducial system; and (5) housekeeping, data handling, instrumentation and telemetry electronics. The design, tests, and operation are described
Physical interpretation of NUT solution
We show that the well-known NUT solution can be correctly interpreted as
describing the exterior field of two counter-rotating semi-infinite sources
possessing negative masses and infinite angular momenta which are attached to
the poles of a static finite rod of positive mass.Comment: 7 pages, 1 figure, submitted to Classical and Quantum Gravit
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