35,396 research outputs found
The art and science of black hole mergers
The merger of two black holes is one of the most extraordinary events in the
natural world. Made of pure gravity, the holes combine to form a single hole,
emitting a strong burst of gravitational radiation. Ground-based detectors are
currently searching for such bursts from holes formed in the evolution of
binary stars, and indeed the very first gravitational wave event detected may
well be a black-hole merger. The space-based LISA detector is being designed to
search for such bursts from merging massive black holes in the centers of
galaxies, events that would emit many thousands of solar masses of pure
gravitational wave energy over a period of only a few minutes. To assist
gravitational wave astronomers in their searches, and to be in a position to
understand the details of what they see, numerical relativists are performing
supercomputer simulations of these events. I review here the state of the art
of these simulations, what we have learned from them so far, and what
challenges remain before we have a full prediction of the waveforms to be
expected from these events.Comment: 12 pages, 3 figures, Proceedings of "Growing Black Holes", Garching
21-25 June 200
Sources of radiation from neutron stars
I give a brief introduction to the problem of detecting gravitational
radiation from neutron stars. After a review of the mechanisms by which such
stars may produce radiation, I consider the different search strategies
appropriate to the different kinds of sources: isolated known pulsars, neutron
stars in binaries, and unseen neutron stars. The problem of an all-sky survey
for unseen stars is the most taxing one that we face in analysing data from
interferometers. I describe the kinds of hierarchical methods that are now
being investigated to reach the maximal sensitivity, and I suggest a
replacement for standard Fourier-transform search methods that requires fewer
floating-point operations for Fourier-based searches over large parameter
spaces, and in addition is highly parallelizable, working just as well on a
loosely coupled network of workstations as on a tightly coupled parallel
computer.Comment: 11 pages, no figure
Getting Ready for GEO600 Data
Data of good quality is expected from a number of gravitational wave
detectors within the next two years. One of these, GEO600, has special
capabilities, such as narrow-band operation. I describe here the preparations
that are currently being made for the analysis of GEO600 data.Comment: 17 pages, 7 figures, proceedings of Yukawa International Seminar 199
Sources of gravitational waves
Sources of low frequency gravitational radiation are reviewed from an astrophysical point of view. Cosmological sources include the formation of massive black holes in galactic nuclei, the capture by such holes of neutron stars, the coalescence of orbiting pairs of giant black holes, and various means of producing a stochastic background of gravitational waves in the early universe. Sources local to our Galaxy include various kinds of close binaries and coalescing binaries. Gravitational wave astronomy can provide information that no other form of observing can supply; in particular, the positive identification of a cosmological background originating in the early universe would be an event as significant as was the detection of the cosmic microwave background
Gravitational Wave Astronomy: Delivering on the Promises
Now that LIGO and Virgo have begun to detect gravitational wave events with
regularity, the field of gravitational wave astronomy is beginning to realise
its promise. Binary black holes and, very recently, binary neutron stars have
been observed, and we are already learning much from them. The future, with
improved sensitivity, more detectors, and detectors like LISA in different
frequency bands, has even more promise to open a completely hidden side of the
Universe to our exploration.Comment: 12 pages, 1 figure, presented at a discussion meeting "Promises of
gravitational wave astronomy" held at the Royal Society London, 11 September
201
INTERNATIONAL MARKETS AND TRADE: AN IMPORTANT COMPONENT IN EXTENSION PROGRAMS
International Relations/Trade,
An optical VLA on the Moon
Optical observations on the Earth must cope with the refractive disturbances of the atmosphere, perturbations by the day-to-night thermal cycle, vibrations induced by the wind, and the bending of the telescope by gravity. These all conspire to limit telescope performance. In particular, in trying to improve angular resolution, there seems to be a practical limit of the order of a few tenths of an arc-second for the realizable angular resolution of single-aperture telescopes, largely imposed by the atmosphere, although other structural limitations would appear as limits at one-tenth of an arc-second or so
- …