Astronomy: LIGO

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LIGO The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves. Prior to LIGO, all data about the universe has come in the form of light and other forms of electromagnetic radiation, from limited direct exploration on relatively nearby Solar System objects such as the Moon, Mars, Venus, Jupiter and their moons, asteroids etc, and from high energy cosmic particles.

Commentary

Source: Wikipedia (CC BY-SA)

Commentary

Source: Internal

Why LIGO matters: Every mission and telescope pushes the boundary of what humanity can observe and understand. These instruments are our eyes and hands reaching into the cosmos. Two additional, smaller gravitational wave observatories are now operational in Japan (KAGRA) and Italy (Virgo). The two LIGO observatories use mirrors spaced 4 kilometres (13,000 ft) apart to measure changes in length—over an effective span of 1,120 kilometres (700 mi)—of less than one ten-thousandth the charge diameter of a proton. The initial LIGO observatories were funded by the United States National Science Foundation (NSF). They were conceived, built, and are operated by Caltec h and MIT. They collected data from 2002 to 2010, but no gravitational waves were detected during that period. 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. 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 1,000 scientists worldwide, as well as 440,000 active Einstein@Home users as of December 2016. LIGO is the largest and most ambitious project ever funded by the NSF. In 2017, the Nobel Prize in Physics was awarded to Rainer Weiss, Kip Thorne and Barry Barish "for decisive contributions to the LIGO detector and the observation of gravitational waves". Observations are made in "runs". As of February 2026, LIGO has made four runs (with the third run divided into two "subruns" and the fourth divided into three subruns), and made 391 detections of gravitational waves. Maintenance and upgrades of the detectors are made between runs. The first run, O1, which ran from September 12, 2015, to January 19, 2016, made the first three detections, all black hole mergers. The second run, O2, which ran from November 30, 2016, to August 25, 2017, made eight detections: seven black hole mergers and the first neutron star merger. The third run, O3, began on April 1, 2019; it was divided into O3a, from April 1 to September 30, 2019, and O3b, from November 1, 2019 until it was suspended on March 27, 2020, due to COVID-19. The O3 run included the first detection of the merger of a neutron star with a black hole. The fourth run, O4, began on May 24, 2023, and ended on November 18, 2025. 250 detection "candidates" were observed during O4, with 77 confirmed observations and the remaining 173 pending final analysis as of February 2026 . Subsequent gravitational wave observatories Virgo in Italy, and KAGRA in Japan, which both use interferometer arms 3 kilometres (9,800 ft) long, coordinated with LIGO to continue observations after the COVID-caused stop, and LIGO's O4 observing run started on May 24, 2023. LIGO projects a sensitivity goal of 160–190 Mpc for binary neutron star mergers (sensitivities: Virgo 80–115 Mpc, KAGRA greater than 1 Mpc).

Commentary

Source: Internal

Deep dive: LIGO The two LIGO observatories use mirrors spaced 4 kilometres (13,000 ft) apart to measure changes in length—over an effective span of 1,120 kilometres (700 mi)—of less than one ten-thousandth the charge diameter of a proton. The initial LIGO observatories were funded by the United States National Science Foundation (NSF). They were conceived, built, and are operated by Caltech and MIT. They collected data from 2002 to 2010, but no gravitational waves were detected during that period. The Advanced LIGO Project to enhance the original LIGO detectors began in 2008, and continues to be supported by the NSF, w ith important contributions from the United Kingdom's Science and Technology Facilities Council, the Max Planck Society of Germany, and the Australian Research Council. 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 1,000 scientists worldwide, as well as 440,000 active Einstein@Home users as of December 2016. LIGO is the largest and most ambitious project ever funded by the NSF. In 2017, the Nobel Prize in Physics was awarded to Rainer Weiss, Kip Thorne and Barry Barish "for decisive contributions to the LIGO detector and the observation of gravitational waves". Observations are made in "runs". As of February 2026, LIGO has made four runs (with the third run divided into two "subruns" and the fourth divided into three subruns), and made 391 detections of gravitational waves. Maintenance and upgrades of the detectors are made between runs. The first run, O1, which ran from September 12, 2015, to January 19, 2016, made the first three detections, all black hole mergers. The second run, O2, which ran from November 30, 2016, to August 25, 2017, made eight detections: seven black hole mergers and the first neutron star merger. The third run, O3, began on April 1, 2019; it was divided into O3a, from April 1 to September 30, 2019, and O3b, from November 1, 2019 until it was suspended on March 27, 2020, due to COVID-19. The O3 run included the first detection of the merger of a neutron star with a black hole. The fourth run, O4, began on May 24, 2023, and ended on November 18, 2025. 250 detection "candidates" were observed during O4, with 77 confirmed observations and the remaining 173 pending final analysis as of February 2026 . Subsequent gravitational wave observatories Virgo in Italy, and KAGRA in Japan, which both use interferometer arms 3 kilometres (9,800 ft) long, coordinated with LIGO to continue observations after the COVID-caused stop, and LIGO's O4 observing run started on May 24, 2023. LIGO projects a sensitivity goal of 160–190 Mpc for binary neutron star mergers (sensitivities: Virgo 80–115 Mpc, KAGRA greater than 1 Mpc). Source: https://en.wikipedia.org/wiki/LIGO (Wikipedia, CC BY-SA)