Contacts:
- Bruce Allen, University of Wisconsin, Milwaukee, (414) 229-6439, ballen@uwm.edu
- Albert Lazzarini, California Institute of Technology, (626) 395-8444, lazz@ligo.caltech.edu
- Roy Williams, California Institute of Technology, (626) 395-3670, roy@cacr.caltech.edu
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a facility dedicated to the detection of cosmic gravitational waves and the harnessing of these waves for scientific research. It will consist of two widely separated installations within the United States, operated in unison as a single observatory. When it reaches maturity, this observatory will be open for use by the national community and will become part of a planned worldwide network of gravitational-wave observatories.
Gravitational waves are ripples in the fabric of space and time produced by violent events in the distant universe, for example by the collision of two black holes or by the cores of supernova explosions. Gravitational waves are emitted by accelerating masses much as electromagnetic waves are produced by accelerating charges. These ripples in the space-time fabric travel to Earth, bringing with them information about their violent origins and about the nature of gravity.
Albert Einstein predicted the existence of these gravitational waves in 1916 in his general theory of relativity, but only now, in the 1990s, has technology become powerful enough to permit detecting them and harnessing them for science. Although they have not yet been detected directly, the influence of gravitational waves on a binary pulsar (two neutron stars orbiting each other) has been measured accurately and is in good agreement with the predictions. Scientists therefore have great confidence that gravitational waves exist. Joseph Taylor and Russel Hulse were awarded the 1993 Nobel Prize in Physics for their discovery of this binary pulsar.
The data challenge of LIGO stems from the very small expected size of the signal in comparison to noise sources (seismic, acoustic, electrical, and many others), and from the great rarity of the events to be detected (less than one per year). Many other data channels must be monitored in addition to the gravity-wave instrument itself, and their effects carefully subtracted. Large amounts of peripheral data must be stored, since the confirmation of a candidate inspiral event will demand very close examination.
 This image is an artist's rendition of two neutron stars merging to form a black hole. Gravitational radiation strips energy from the orbiting stars, which spiral toward each other until they merge with a vast release of energy. LIGO, it is hoped, will detect such events.
These pictures show one of the two LIGO laboratories, in Hanford, Washington (shown here), the other in Livingston, Louisiana. There are two 4km arms at right angles, each with laser beams in high vacuum. The objective is to detect changes in length a thousand times smaller than an atomic nucleus.
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