6.2 Polarization of gravitational waves6 Gravitational Wave Tests of 6 Gravitational Wave Tests of

6.1 Gravitational wave observatories

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 tex2html_wrap_inline5535 (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 (tex2html_wrap_inline5537). 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 tex2html_wrap_inline5539 and tex2html_wrap_inline5541 Hz, with peak strain sensitivity of order tex2html_wrap_inline5543  [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.

6.2 Polarization of gravitational waves6 Gravitational Wave Tests of 6 Gravitational Wave Tests of

image The Confrontation between General Relativity and Experiment
Clifford M. Will
© Max-Planck-Gesellschaft. ISSN 1433-8351
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