Stationary configurations of two extreme black holes obtainable from the Kinnersley-Chitre solution

Stationary axisymmetric systems of two extreme Kerr sources separated by a massless strut, which arise as subfamilies of the well-known Kinnersley-Chitre solution, are studied. We present explicit analytical formulas for the individual masses and angular momenta of the constituents and establish the range of the parameters for which such systems can be regarded as describing black holes. The mass-angular momentum relations and the interaction force in the black-hole configurations are also analyzed. Furthermore, we construct a charging generalization of the Kinnersley-Chitre metric and, as applications of the general formulas obtained, discuss two special cases describing a pair of identical co- and counterrotating extreme Kerr-Newman black holes kept apart by a conical singularity. From our analysis it follows in particular that the equality $m^2-a^2-e^2=0$ relating the mass, angular momentum per unit mass and electric charge of a single Kerr-Newman extreme black hole is no longer verified by the analogous extreme black-hole constituents in binary configurations.Comment: final version revised according to referee's suggestion

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

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

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

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

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