279 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
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
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
Time-Symmetric ADI and Causal Reconnection: Stable Numerical Techniques for Hyperbolic Systems on Moving Grids
Moving grids are of interest in the numerical solution of hydrodynamical
problems and in numerical relativity. We show that conventional integration
methods for the simple wave equation in one and more than one dimension exhibit
a number of instabilities on moving grids. We introduce two techniques, which
we call causal reconnection and time-symmetric ADI, which together allow
integration of the wave equation with absolute local stability in any number of
dimensions on grids that may move very much faster than the wave speed and that
can even accelerate. These methods allow very long time-steps, are fully
second-order accurate, and offer the computational efficiency of
operator-splitting.Comment: 45 pages, 19 figures. Published in 1994 but not previously available
in the electronic archive
End-to-end algorithm for hierarchical area searches for long-duration GW sources for GEO 600
We describe a hierarchical, highly parallel computer algorithm to perform
searches for unknown sources of continuous gravitational waves -- spinning
neutron stars in the Galaxy -- over wide areas of the sky and wide frequency
bandwidths. We optimize the algorithm for an observing period of 4 months and
an available computing power of 20 Gflops, in a search for neutron stars
resembling millisecond pulsars. We show that, if we restrict the search to the
galactic plane, the method will detect any star whose signal is stronger than
15 times the noise level of a detector over that search period. Since
on grounds of confidence the minimum identifiable signal should be about 10
times noise, our algorithm does only 50% worse than this and runs on a computer
with achievable processing speed.Comment: 7 pages, for proceedings of Jan 1999 Moriond meeting "Gravitational
Waves and Experimental Gravity
The generalized F-statistic: multiple detectors and multiple GW pulsars
The F-statistic, derived by Jaranowski, Krolak & Schutz (1998), is the
optimal (frequentist) statistic for the detection of nearly periodic
gravitational waves from known neutron stars, in the presence of stationary,
Gaussian detector noise. The F-statistic was originally derived for the case of
a single detector, whose noise spectral density was assumed constant in time,
and for a single known neutron star. Here we show how the F-statistic can be
straightforwardly generalized to the cases of 1) a network of detectors with
time-varying noise curves, and 2) a population of known sources. Fortunately,
all the important ingredients that go into our generalized F-statistics are
already calculated in the single-source/single-detector searches that are
currently implemented, e.g., in the LIGO Software Library, so implementation of
optimal multi-detector, multi-source searches should require negligible
additional cost in computational power or software development.Comment: 6 pages, 0 figures, submitted to PRD; section IV substantially
enlarged and revised, and a few typos correcte
Constraining the Equation of State with Moment of Inertia Measurements
We estimate that the moment of inertia of star A in the recently discovered
double pulsar system PSR J0737-3039 may be determined after a few years of
observation to something like 10% accuracy. This would enable accurate
estimates of the radius of the star and the presure of matter in the vicinity
of 1 to 2 times the nuclear saturation density, which would in turn provide
strong constraints on the equation of state of neutron stars and the physics of
their interiors.Comment: Submitted to ApJ, 4 figure
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