Editing LIGO (section)

==Mission==
[[File:LIGO detector sensitivity curve.png|thumb|300px|upright=2| Detector noise curves for Initial and Advanced LIGO as a function of frequency. They lie above the bands for space-borne detectors like the [[Laser Interferometer Space Antenna|evolved Laser Interferometer Space Antenna]] (eLISA) and [[pulsar timing array]]s such as the [[European Pulsar Timing Array]] (EPTA). The characteristic strains of potential astrophysical sources are also shown. To be detectable the characteristic strain of a signal must be above the noise curve.<ref>{{cite web |title=Gravitational Wave Detectors and Sources |url=http://rhcole.com/apps/GWplotter/ |access-date=20 April 2014 |last1=Moore |first1=Christopher |last2=Cole |first2=Robert |last3=Berry |first3=Christopher |date=19 July 2013}}</ref> These frequencies that aLIGO can detect are in the range of [[Hearing#Frequency range|human hearing]].]]

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 [[Russell Alan Hulse|Hulse]] and [[Joseph Hooton Taylor, Jr.|Taylor]] for this discovery.<ref>{{cite web | title=The Nobel Prize in Physics 1993: Russell A. Hulse, Joseph H. Taylor Jr. |url=https://www.nobelprize.org/nobel_prizes/physics/laureates/1993/ |website=nobelprize.org}}</ref>

Direct detection of gravitational waves had long been sought. Their discovery has launched a new branch of astronomy to complement [[Electromagnetic radiation|electromagnetic]] telescopes and [[neutrino]] observatories. [[Joseph Weber]] pioneered the effort to detect gravitational waves in the 1960s through his work on [[Weber bar|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.<ref name="obituary">{{cite web |title=Obituary: Dr. Robert L. Forward |url=http://www.spaceref.com/news/viewpr.html?pid=9328 |archive-url=https://archive.today/20130902222420/http://www.spaceref.com/news/viewpr.html?pid=9328 |url-status=dead |archive-date=2 September 2013 |website=www.spaceref.com |date=21 September 2002 |access-date=3 September 2018 |language=en }}</ref>

In fact as early as the 1960s, and perhaps before that, there were papers published on wave resonance of light and gravitational waves.<ref>{{cite journal|author=M.E. Gertsenshtein|title=Wave Resonance of Light and Gravitational Waves|journal=JETP|volume=41|issue=1|pages=113–114|year=1961|url=http://www.jetp.ac.ru/cgi-bin/e/index/e/14/1/p84?a=list|access-date=19 January 2016|archive-date=6 February 2016|archive-url=https://web.archive.org/web/20160206055044/http://www.jetp.ac.ru/cgi-bin/e/index/e/14/1/p84?a=list|url-status=dead}}</ref> 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.<ref>{{Cite journal |title=On the detection of low frequency gravitational waves |first1=M. E. |last1=Gertsenshtein |first2=V. I. |last2=Pustovoit |journal=[[Journal of Experimental and Theoretical Physics|JETP]] |volume=43 |pages=605–607 |date=August 1962}}</ref> The authors argued that by using interferometers the sensitivity can be 10<sup>7</sup> to 10<sup>10</sup> times better than by using electromechanical experiments. Later, in 1965, [[Vladimir Braginsky|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.

Since the early 1990s, physicists have thought that technology has evolved to the point where detection of [[gravitational wave]]s—of significant astrophysical interest—is now possible.<ref>{{Cite journal| title= Astrophysical Sources of Gravitational Radiation |journal= [[Annual Review of Nuclear and Particle Science]]|volume= 44|issue= 44|pages= 655–717|doi= 10.1146/annurev.ns.44.120194.003255| doi-access=free|year= 1994|last1= Bonazzola|first1= S|last2= Marck|first2= J A|bibcode= 1994ARNPS..44..655B}}</ref>

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 star]]s 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 [[Big Bang|birth of the universe]]. The observatory may, in theory, also observe more exotic hypothetical phenomena, such as gravitational waves caused by oscillating [[cosmic string]]s or colliding [[Domain wall (string theory)|domain walls]].