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The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment aiming to directly detect gravitational waves. Cofounded in 1992 by Kip Thorne and Ronald Drever of Caltech and Rainer Weiss of MIT, LIGO is a joint project between scientists at MIT, Caltech, and many other colleges and universities. Scientists involved in the project and the analysis of the data for gravitational-wave astronomy are organised by the LIGO Scientific Collaboration. LIGO is funded by the National Science Foundation (NSF), with important contributions from the UK Science and Technology Facilities Council, the Max Planck Society of Germany, and the Australian Research Council. At the cost of $620 million, it is the largest and most ambitious project ever funded by the NSF.〔Larger physics projects in the United States, such as Fermilab, have traditionally been funded by the Department of Energy.〕〔(LIGO Fact Sheet at NSF )〕 Initial LIGO operations between 2002 and 2010 did not detect any gravitational waves. This was followed by a multi-year shutdown while the detectors were replaced by much improved "Advanced LIGO" versions. As of February 2015, two such advanced detectors (one in Livingston, Louisiana and the other in Hanford, Washington) have been brought into engineering mode.〔(【引用サイトリンク】url=https://www.advancedligo.mit.edu/feb_2015_news.html )〕 On September 18, 2015, Advanced LIGO became fully operational and began formal science operations at twice the sensitivity of the initial LIGO interferometers. ==Mission== LIGO's mission is to directly observe gravitational waves of cosmic origin. These waves were first predicted by Einstein's general theory of relativity in 1916, when the technology necessary for their detection did not yet exist. Their existence was indirectly confirmed when observations of the binary pulsar PSR 1913+16 in 1974 showed an orbital decay which matched Einstein's predictions of energy loss by gravitational radiation. The Nobel Prize in Physics 1993 was awarded to Hulse and Taylor for this discovery.〔(【引用サイトリンク】url=http://www.nobelprize.org/nobel_prizes/physics/laureates/1993/ )〕 Direct detection of gravitational waves has long been sought. Their discovery would launch a new branch of astronomy to complement electromagnetic telescopes and neutrino observatories. Joseph Weber pioneered the effort to detect gravitational waves in the 1960s through his work on resonant mass bar detectors. Bar detectors continue to be used at six sites worldwide. By the 1970s, scientists including Rainer Weiss realized the applicability of laser interferometry to gravitational wave measurements. Robert Forward operated an interferometric detector at Hughes in the early 1970s.〔(California Institute of Technology announces death of Robert L Forward ) September 22, 2002〕 In fact as early as the 1960s, and perhaps before that, there were papers published on wave resonance of light and gravitational waves.〔V. B. Braginsky, L. P. Grishchuck, A. G. Doroshkevich, M .B. Mensky, I.D.Novikov, M. V. Sazhin and Y. B. Zeldovisch〕 Work was published in 1971 on methods to exploit this resonance for the detection of high-frequency gravitational waves. In 1962, M. E. Gertsenshtein and V. I. Pustovoit published the very first paper describing the principles for using interferometers for the detection of very long wavelength gravitational waves. The authors argued that by using interferometers the sensitivity can be 107–1010 times better than by using electromechanical experiments. Later, in 1965, Braginsky, extensively discussed gravitational-wave sources and their possible detection. He pointed out the 1962 paper and mentioned the possibility of detecting gravitational waves if the interferometric technology and measuring techniques improved. In August 2002, LIGO began its search for cosmic gravitational waves. Measurable emissions of gravitational waves are expected from binary systems (collisions and coalescences of neutron stars or black holes), supernova explosions of massive stars (which form neutron stars and black holes), accreting neutron stars, rotations of neutron stars with deformed crusts, and the remnants of gravitational radiation created by the birth of the universe. The observatory may, in theory, also observe more exotic hypothetical phenomena, such as gravitational waves caused by oscillating cosmic strings or colliding domain walls. Since the early 1990s, physicists have thought that technology has evolved to the point where detection of gravitational waves—of significant astrophysical interest—is now possible. ==Observatories== LIGO operates two gravitational wave observatories in unison: the LIGO Livingston Observatory () in Livingston, Louisiana, and the LIGO Hanford Observatory, on the DOE Hanford Site (), located near Richland, Washington. These sites are separated by 3,002 kilometers (1,865 miles). Since gravitational waves are expected to travel at the speed of light, this distance corresponds to a difference in gravitational wave arrival times of up to ten milliseconds. Through the use of triangulation, the difference in arrival times can determine the source of the wave in the sky. Each observatory supports an L-shaped ultra high vacuum system, measuring 4 kilometers (2.5 miles) on each side. Up to five interferometers can be set up in each vacuum system. The LIGO Livingston Observatory houses one laser interferometer in the primary configuration. This interferometer was successfully upgraded in 2004 with an active vibration isolation system based on hydraulic actuators providing a factor of 10 isolation in the 0.1 – 5 Hz band. Seismic vibration in this band is chiefly due to microseismic waves and anthropogenic sources (traffic, logging, etc.). The LIGO Hanford Observatory houses one interferometer, almost identical to the one at the Livingston Observatory. During the Initial and Enhanced LIGO eras, a half-length interferometer was operated in parallel with the main interferometer. For this 2 km interferometer, the Fabry–Pérot arm cavities had the same optical finesse, and thus half the storage time, as the 4 km interferometers. With half the storage time, the theoretical strain sensitivity was as good as the full length interferometers above 200 Hz but only half as good at low frequencies. During the same era, Hanford retained its original passive seismic isolation system due to limited geologic activity in Southeastern Washington. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「LIGO」の詳細全文を読む スポンサード リンク
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