

Some time in the next decade, a new opportunity for testing
relativistic gravity will be realized, with the commissioning and
operation of kilometer-scale, laser interferometric gravitational
wave observatories in the U.S. (LIGO project), Europe (VIRGO and
GEO600 projects) and Japan (TAMA300 project). Gravitational-wave
searches at these observatories are scheduled to commence around
2002. The LIGO broad-band antennas will have the capability of
detecting and measuring the gravitational waveforms from
astronomical sources in a frequency band between about 10 Hz (the
seismic noise cutoff) and 500 Hz (the photon counting noise
cutoff), with a maximum sensitivity to strain at around 100 Hz of
(rms). The most promising source for detection and study of the
gravitational wave signal is the ``inspiralling compact binary''
- a binary system of neutron stars or black holes (or one of
each) in the final minutes of a death dance leading to a violent
merger. Such is the fate, for example, of the Hulse-Taylor binary
pulsar PSR 1913+16 in about 300 million years. Given the expected
sensitivity of the ``advanced LIGO'' (around 2007), which could
see such sources out to hundreds of megaparsecs, it has been
estimated that from 3 to 100 annual inspiral events could be
detectable. Other sources, such as supernova core collapse
events, instabilities in rapidly rotating nascent neutron stars,
signals from non-axisymmetric pulsars, and a stochastic
background of waves, may be detectable (for reviews, see [1,
127]; for updates on the status of various projects, see [65,
32]).
A similar network of cryogenic resonant-mass gravitational
antennas have been in operation for many years, albeit at lower
levels of sensitivity (
). While modest improvements in sensitivity may be expected in
the future, these resonant detectors are not expected to be
competitive with the large interferometers, unless new designs
involving bars of spherical, or nearly spherical shape come to
fruition. These systems are primarily sensitive to waves in
relatively narrow bands about frequencies in the hundreds to
thousands of Hz range [104,
73,
14,
110].
In addition, plans are being developed for an orbiting laser
interferometer space antenna (LISA for short). Such a system,
consisting of three spacecraft separated by millions of
kilometers, would be sensitive primarily in the very low
frequency band between
and
Hz, with peak strain sensitivity of order
[54].
In addition to opening a new astronomical window, the detailed
observation of gravitational waves by such observatories may
provide the means to test general relativistic predictions for
the polarization and speed of the waves, and for gravitational
radiation damping.


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The Confrontation between General Relativity and
Experiment
Clifford M. Will
http://www.livingreviews.org/lrr-2001-4
© Max-Planck-Gesellschaft. ISSN 1433-8351
Problems/Comments to
livrev@aei-potsdam.mpg.de
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