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Two sites for catching gravitational waves.

Situated on an arid plateau in central Washington state, the Department of Energy's vast Hanford Reservation has long served as a center for the extraction of plutonium from spent nuclear fuel. Last week, the National Science Foundation (NSF) designated a site on the Hanford Reservation as one of two locations for the twin facilities of a unique, sophisticated observatory dedicated to the detection of a very different, much more elusive type of radiation - gravitational waves. The other chosen site lies in a flat, wooded area near Livingston, La., about 30 miles east of Baton Rouge.

Following more than a decade of feasibility studies and political wrangling, this decision clears the way for construction of the Laser Interferometer Grvitational-Wave Observatory (LIGO). "Overall, I am convinced that the Louisiana-Washington sites will best serve the scientific objectives of this important project," says NSF Director Walter E. Massey, who made the decision.

Consisting of two facilities separated by at least 2,400 kilometers but operating in unison to avoid false signals, the observatory will cost about $210 million and take five years to build. Last October, Congress approved $23.5 million in first-year funding to cover the costs of selecting the sites, completing the engineering design of the facilities and starting site preparation.

The building of LIGO represents a bold gamble to detect the distinctive imprint of gravitational waves resulting from such violent cosmic events as the collapse of stellar cores and collisions between black holes. The project furnishes an important means of testing Einstein's general theory of relativity, in which massive bodies such as stars influence other objects not by acting on them directly but instead by warping space and time.

When such a body abruptly changes its motion or its mass, the space-time in its vicinity undergoes a corresponding convulsion. This disturbance travels outward as a gravitational wave that jostles any objects in its path.

To detect a gravitational wave passing through Earth, each LIGO facility will have two evacuated steel pipes, 4 feet in diameter and 2.5 miles long, extending at right angles to each other. Laser light will pass up and down the pipes, bouncing between pairs of mirrors attached to heavy weights.

A gravitational wave passing through the facility would imperceptibly move one set of weights closer together and the other farther apart. That slight change in the distance traveled by the laser beams in the two branches would show up as a shift in the interference pattern created where the two beams recombine.

A tend of scientists from the California Institute of Technology in Pasadena, location of an experimental prototype facility, and the Massachusetts Institute of Technology will oversee the construction and operation of the LIGO facilities.
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Author:Peterson, Ivars
Publication:Science News
Date:Feb 29, 1992
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