LIGO

Laser Interferometer Gravitational Wave Observatory

The LIGO Livingston control room as it was during Advanced LIGO's first observing run (O1)
Alternative names	LIGO
Location(s)	Hanford Site, Washington and Livingston, Louisiana, US
Coordinates	LIGO 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 / 30.5628944°N 90.7742417°W / 30.5628944; -90.7742417 (LIGO Livingston Observatory)
Organization	LIGO Scientific Collaboration
Wavelength	43 km (7.0 kHz)–10,000 km (30 Hz)
Built	1994–2002 (1994–2002)
First light	23 August 2002
Telescope style	gravitational-wave observatory
Length	4,000 m (13,123 ft 4 in)
Website	www.ligo.caltech.edu
LIGO Livingston Observatory LIGO Hanford Observatory LIGO observatories in the Contiguous United States
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The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed 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 observatories use mirrors spaced four kilometers apart which are capable of detecting a change^{[clarification needed]} of less than one ten-thousandth the charge diameter of a proton.^[2]

The initial LIGO observatories were funded by the United States 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 United Kingdom's 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^[update].^[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]

Observations are made in "runs". As of January 2022^[update], LIGO has made three runs (with one of the runs divided into two "subruns"), and made 90 detections of gravitational waves.^[14][15] Maintenance and upgrades of the detectors are made between runs. The first run, O1, which ran from 12 September 2015 to 19 January 2016, made the first three detections, all black hole mergers. The second run, O2, which ran from 30 November 2016 to 25 August 2017, made eight detections: seven black hole mergers and the first neutron star merger.^[16] The third run, O3, began on 1 April 2019; it was divided into O3a, from 1 April to 30 September 2019, and O3b, from 1 November 2019^[17] until it was suspended on 27 March 2020 due to COVID-19.^[18] The O3 run made the first detection of a merger of a neutron star with a black hole.^[15]

The gravitational wave observatories LIGO, Virgo in Italy, and KAGRA in Japan are coordinating to continue observations after the COVID-caused stop, and LIGO's O4 observing run started on 24 May 2023.^[19][20] LIGO projects a sensitivity goal of 160–190 Mpc for binary neutron star mergers (sensitivities: Virgo 80–115 Mpc, KAGRA greater than 1 Mpc).^[21]