3,477 research outputs found
Non-existence of stationary two-black-hole configurations
We resume former discussions of the question, whether the spin-spin repulsion
and the gravitational attraction of two aligned black holes can balance each
other. To answer the question we formulate a boundary value problem for two
separate (Killing-) horizons and apply the inverse (scattering) method to solve
it. Making use of results of Manko, Ruiz and Sanabria-G\'omez and a novel black
hole criterion, we prove the non-existence of the equilibrium situation in
question.Comment: 15 pages, 3 figures; Contribution to Juergen Ehlers Memorial Issue
(GeRG journal
Space missions to comets
The broad impact of a cometary mission is assessed with particular emphasis on scientific interest in a fly-by mission to Halley's comet and a rendezvous with Tempel 2. Scientific results, speculations, and future plans are discussed
Near Infrared Imaging of the Hubble Deep Field with The Keck Telescope
Two deep K-band () images, with point-source detection limits of
mag (one sigma), taken with the Keck Telescope in subfields of the
Hubble Deep Field, are presented and analyzed. A sample of objects to K=24 mag
is constructed and and colors are measured. By
stacking visually selected objects, mean colors can be measured to
very faint levels; the mean color is constant with apparent
magnitude down to mag.Comment: Replaced with slightly revised source positions and corrected V-I
magnitudes (which were incorrect in the Tables and Figure 5). 18 pages. The
data are publicly available at http://www.cco.caltech.edu/~btsoifer/hdf.html
along with a high-resolution version of Fig.
Harrison transformation of hyperelliptic solutions and charged dust disks
We use a Harrison transformation on solutions to the stationary axisymmetric
Einstein equations to generate solutions of the Einstein-Maxwell equations. The
case of hyperelliptic solutions to the Ernst equation is studied in detail.
Analytic expressions for the metric and the multipole moments are obtained. As
an example we consider the transformation of a family of counter-rotating dust
disks. The resulting solutions can be interpreted as disks with currents and
matter with a purely azimuthal pressure or as two streams of freely moving
charged particles. We discuss interesting limiting cases as the extreme limit
where the charge becomes identical to the mass, and the ultrarelativistic limit
where the central redshift diverges.Comment: 20 pages, 9 figure
Proof of a generalized Geroch conjecture for the hyperbolic Ernst equation
We enunciate and prove here a generalization of Geroch's famous conjecture
concerning analytic solutions of the elliptic Ernst equation. Our
generalization is stated for solutions of the hyperbolic Ernst equation that
are not necessarily analytic, although it can be formulated also for solutions
of the elliptic Ernst equation that are nowhere axis-accessible.Comment: 75 pages (plus optional table of contents). Sign errors in elliptic
case equations (1A.13), (1A.15) and (1A.25) are corrected. Not relevant to
proof contained in pape
The luminosity function of the brightest galaxies in the IRAS survey
Results from a study of the far infrared properties of the brightest galaxies in the IRAS survey are described. There is a correlation between the infrared luminosity and the infrared to optical luminosity ratio and between the infrared luminosity and the far infrared color temperature in these galaxies. The infrared bright galaxies represent a significant component of extragalactic objects in the local universe, being comparable in space density to the Seyferts, optically identified starburst galaxies, and more numerous than quasars at the same bolometric luminosity. The far infrared luminosity in the local universe is approximately 25% of the starlight output in the same volume
Overview study of Space Power Technologies for the advanced energetics program
Space power technologies are reviewed to determine the state-of-the-art and to identify advanced or novel concepts which promise large increases in performance. The potential for incresed performance is judged relative to benchmarks based on technologies which have been flight tested. Space power technology concepts selected for their potentially high performance are prioritized in a list of R & D topical recommendations for the NASA program on Advanced Energetics. The technology categories studied are solar collection, nuclear power sources, energy conversion, energy storage, power transmission, and power processing. The emphasis is on electric power generation in space for satellite on board electric power, for electric propulsion, or for beamed power to spacecraft. Generic mission categories such as low Earth orbit missions and geosynchronous orbit missions are used to distinguish general requirements placed on the performance of power conversion technology. Each space power technology is judged on its own merits without reference to specific missions or power systems. Recommendations include 31 space power concepts which span the entire collection of technology categories studied and represent the critical technologies needed for higher power, lighter weight, more efficient power conversion in space
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