Laser Interferometer Gravitational-Wave Observatory
LLO Control Room.jpg
The LIGO Livingston control room as it was during Advanced LIGO's first observing run (O1)
Alternative namesLIGO Edit this on Wikidata
Location(s)Hanford Site, Livingston, Washington, US
CoordinatesLIGO Hanford Observatory: 46°27′18.52″N 119°24′27.56″W / 46.4551444°N 119.4076556°W / 46.4551444; -119.4076556 (LIGO Hanford Observatory)
LIGO Livingston Observatory: 30°33′46.42″N 90°46′27.27″W / 30°33′46.42″N 90°46′27.27″W / LIGO Livingston Observatory)
OrganizationLIGO Scientific Collaboration Edit this on Wikidata
Wavelength43 km (7.0 kHz)-10,000 km (30 Hz)
Built1994 Edit this on Wikidata–2002 Edit this on Wikidata (1994 Edit this on Wikidata–2002 Edit this on Wikidata) Edit this at Wikidata
First light23 August 2002 Edit this on Wikidata
Telescope stylegravitational-wave observatory Edit this on Wikidata
Length4,000 m (13,123 ft 4 in) Edit this at Wikidata Edit this at Wikidata
LIGO is located in the United States
LIGO Livingston Observatory
LIGO Livingston Observatory
LIGO Hanford Observatory
LIGO Hanford Observatory
LIGO observatories in the Contiguous United States

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool.[1] Two large observatories were built in the United States with the aim of detecting gravitational waves by laser interferometry. These can detect a change in the 4 km mirror spacing of less than a ten-thousandth the charge diameter of a proton.[2]

The initial LIGO observatories were funded by the National Science Foundation (NSF) and were conceived, built and are operated by Caltech and MIT.[3][4] They collected data from 2002 to 2010 but no gravitational waves were detected.

The Advanced LIGO Project to enhance the original LIGO detectors began in 2008 and continues to be supported by the NSF, with important contributions from the UK Science and Technology Facilities Council, the Max Planck Society of Germany, and the Australian Research Council.[5][6] The improved detectors began operation in 2015. The detection of gravitational waves was reported in 2016 by the LIGO Scientific Collaboration (LSC) and the Virgo Collaboration with the international participation of scientists from several universities and research institutions. Scientists involved in the project and the analysis of the data for gravitational-wave astronomy are organized by the LSC, which includes more than 1000 scientists worldwide,[7][8][9] as well as 440,000 active Einstein@Home users as of December 2016.[10]

LIGO is the largest and most ambitious project ever funded by the NSF.[11][12]In 2017, the Nobel Prize in Physics was awarded to Rainer Weiss, Kip Thorne and Barry C. Barish "for decisive contributions to the LIGO detector and the observation of gravitational waves."[13]

As of December 2018, LIGO has made eleven detections of gravitational waves, of which ten are from binary black hole mergers. The other event was the first detection of a collision of two neutron stars, on 17 August 2017 which simultaneously produced optical signals detectable by conventional telescopes. All eleven events were observed in data from the first and second observing runs of Advanced LIGO.[14]



The LIGO concept built upon early work by many scientists to test a component of Albert Einstein's theory of relativity, the existence of gravitational waves. Starting in the 1960s, American scientists including Joseph Weber, as well as Soviet scientists Mikhail Gertsenshtein and Vladislav Pustovoit, conceived of basic ideas and prototypes of laser interferometry,[15][16] and in 1967 Rainer Weiss of MIT published an analysis of interferometer use and initiated the construction of a prototype with military funding, but it was terminated before it could become operational.[17] Starting in 1968, Kip Thorne initiated theoretical efforts on gravitational waves and their sources at Caltech, and was convinced that gravitational wave detection would eventually succeed.[15]

Prototype interferometric gravitational wave detectors (interferometers) were built in the late 1960s by Robert L. Forward and colleagues at Hughes Research Laboratories (with mirrors mounted on a vibration isolated plate rather than free swinging), and in the 1970s (with free swinging mirrors between which light bounced many times) by Weiss at MIT, and then by Heinz Billing and colleagues in Garching Germany, and then by Ronald Drever, James Hough and colleagues in Glasgow, Scotland.[18]

In 1980, the NSF funded the study of a large interferometer led by MIT (Paul Linsay, Peter Saulson, Rainer Weiss), and the following year, Caltech constructed a 40-meter prototype (Ronald Drever and Stan Whitcomb). The MIT study established the feasibility of interferometers at a 1-kilometer scale with adequate sensitivity.[15][19]

Under pressure from the NSF, MIT and Caltech were asked to join forces to lead a LIGO project based on the MIT study and on experimental work at Caltech, MIT, Glasgow, and Garching. Drever, Thorne, and Weiss formed a LIGO steering committee, though they were turned down for funding in 1984 and 1985. By 1986, they were asked to disband the steering committee and a single director, Rochus E. Vogt (Caltech), was appointed. In 1988, a research and development proposal achieved funding.[15][19][20][21][22][23]

From 1989 through 1994, LIGO failed to progress technically and organizationally. Only political efforts continued to acquire funding.[15][24] Ongoing funding was routinely rejected until 1991, when the U.S. Congress agreed to fund LIGO for the first year for $23 million. However, requirements for receiving the funding were not met or approved, and the NSF questioned the technological and organizational basis of the project.[20][21] By 1992, LIGO was restructured with Drever no longer a direct participant.[15][24][25][26] Ongoing project management issues and technical concerns were revealed in NSF reviews of the project, resulting in the withholding of funds until they formally froze spending in 1993.[15][24][27][28]

In 1994, after consultation between relevant NSF personnel, LIGO's scientific leaders, and the presidents of MIT and Caltech, Vogt stepped down and Barry Barish (Caltech) was appointed laboratory director,[15][25][29] and the NSF made clear that LIGO had one last chance for support.[24] Barish's team created a new study, budget, and project plan with a budget exceeding the previous proposals by 40%. Barish proposed to the NSF and National Science Board to build LIGO as an evolutionary detector, where detection of gravitational waves with initial LIGO would be possible, and with advanced LIGO would be probable.[30] This new proposal received NSF funding, Barish was appointed Principal Investigator, and the increase was approved. In 1994, with a budget of US$395 million, LIGO stood as the largest overall funded NSF project in history. The project broke ground in Hanford, Washington in late 1994 and in Livingston, Louisiana in 1995. As construction neared completion in 1997, under Barish's leadership two organizational institutions were formed, LIGO Laboratory and LIGO Scientific Collaboration (LSC). The LIGO laboratory consists of the facilities supported by the NSF under LIGO Operation and Advanced R&D; this includes administration of the LIGO detector and test facilities. The LIGO Scientific Collaboration is a forum for organizing technical and scientific research in LIGO. It is a separate organization from LIGO Laboratory with its own oversight. Barish appointed Weiss as the first spokesperson for this scientific collaboration.[15][20]

Observations begin

Initial LIGO operations between 2002 and 2010 did not detect any gravitational waves. In 2004, under Barish, the funding and groundwork were laid for the next phase of LIGO development (called "Enhanced LIGO"). This was followed by a multi-year shut-down while the detectors were replaced by much improved "Advanced LIGO" versions.[31][32] Much of the research and development work for the LIGO/aLIGO machines was based on pioneering work for the GEO600 detector at Hannover, Germany.[33][34] By February 2015, the detectors were brought into engineering mode in both locations.[35]

By mid-September 2015, "the world's largest gravitational-wave facility" completed a 5-year US$200-million overhaul at a total cost of $620 million.[9][36] On 18 September 2015, Advanced LIGO began its first formal science observations at about four times the sensitivity of the initial LIGO interferometers.[37] Its sensitivity will be further enhanced until it reaches design sensitivity around 2021.[38]


On 11 February 2016, the LIGO Scientific Collaboration and Virgo Collaboration published a paper about the detection of gravitational waves, from a signal detected at 09.51 UTC on 14 September 2015 of two ~30 solar mass black holes merging about 1.3 billion light-years from Earth.[39][40]

Current executive director David Reitze announced the findings at a media event in Washington D.C., while executive director emeritus Barry Barish presented the first scientific paper of the findings at CERN to the physics community.[41]

On 2 May 2016, members of the LIGO Scientific Collaboration and other contributors were awarded a Special Breakthrough Prize in Fundamental Physics for contributing to the direct detection of gravitational waves.[42]

On 16 June 2016 LIGO announced a second signal was detected from the merging of two black holes with 14.2 and 7.5 times the mass of the Sun. The signal was picked up on 26 December 2015, at 3:38 UTC.[43]

The detection of a third black hole merger, between objects of 31.2 and 19.4 solar masses, occurred on 4 January 2017 and was announced on 1 June 2017.[44][45]

A fourth detection of a black hole merger, between objects of 30.5 and 25.3 solar masses, was observed on 14 August 2017 and was announced on 27 September 2017.[46]

In 2017, Weiss, Barish, and Thorne received the Nobel Prize in Physics "for decisive contributions to the LIGO detector and the observation of gravitational waves." Weiss was awarded one-half of the total prize money, and Barish and Thorne each received a one-quarter prize.[47][48][49]

LIGO resumed operation after shutdown for improvements on 26 March 2019, with Virgo expected to join the network 1 April 2019.[50]