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A facility dedicated to the detection and measurement of cosmic gravitational waves.
It consists of two widely separated installations, or detectors, within the United
States, operated in unison as a single observatory. One installation is located in
Hanford (Washington) and the other in Livingston (Louisiana), 3,000 km apart. Funded
by the National Science Foundation (NSF), LIGO was designed and constructed by a team
of scientists from the California Institute of Technology, the Massachusetts Institute
of Technology, and by industrial contractors. Construction of the facilities was completed
in 1999. Initial operation of the detectors began in 2001. Each LIGO detector beams
laser light down arms 4 km long, which are arranged in the shape of an 'L.' If a gravitational
wave passes through the detector system, the distance traveled by the laser beam changes
by a minuscule amount -- less than one-thousandth of the size of an atomic nucleus
(10^-18 m). Still, LIGO should be able to pick this difference up. LIGO directly detected
gravitational waves for the first time from a binary black hole merger (GW150914)
on September 14, 2015. The Nobel Prize in physics 2017 was awarded to three physicists
(Rainer Weiss, Barry C. Barish, and Kip S. Thorne) for decisive contributions to the
LIGO detector and the observation of gravitational waves. LIGO had a prominent role
in the detection of GW170817, the first event with an electromagnetic counterpart.
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