⏾ Concept Map

LIGO ○´｜Definition｜1st｜20260912121615-00-⌔

LIGO - Wikipedia

LIGO

📊 ➺ 🖼️ ➺

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves.1 Prior to LIGO, all data about the universe had 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. Initially, two large observatories were built in the United States with the aim of detecting gravitational waves by laser interferometry. Two additional, smaller gravitational wave observatories are now operational: one in Japan (KAGRA), and one in 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.2

The initial LIGO observatories were funded by the United States National Science Foundation (NSF). They were conceived, built, and are operated by Caltech and MIT34 in the 1990s. They started to collect 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.56 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,789 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.1112 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”.13

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.1414 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.15 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, 201916 until it was suspended on March 27, 2020, due to COVID-19.17 The O3 run included the first detection of the merger of a neutron star with a black hole.14 The fourth run, O4, began on May 24, 2023, and ended on November 18, 2025. A total of 250 detection “candidates” were observed during O4, with 77 confirmed observations and the remaining 173 pending final analysis as of February 2026.18

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, with LIGO’s O4 observing run operating from May 24, 2023 to November 18, 2025.1920 During this time, LIGO had a sensitivity of 160–190 Mpc for binary neutron star mergers (sensitivities: Virgo 80–115 Mpc, KAGRA greater than 1 Mpc).21

Printed 2026-09-12.

(echo:: @ ᯤ)

Footnotes

  1. Barish, Barry C.; Weiss, Rainer (October 1999). “LIGO and the Detection of Gravitational Waves”. Physics Today. 52 (10): 44. Bibcode:1999PhT…52j..44B. doi:10.1063/1.882861. ↩

  2. “Facts”. LIGO. Archived from the original on July 4, 2017. Retrieved August 24, 2017. This is equivalent to measuring the distance from Earth to the nearest star to an accuracy smaller than the width of a human hair! (that is, to Proxima Centauri at 4.0208 × 10 km). ↩

  3. “LIGO Lab Caltech MIT”. Archived from the original on September 1, 2021. Retrieved June 24, 2016. ↩

  4. “LIGO MIT”. Archived from the original on September 27, 2020. Retrieved June 24, 2016. ↩

  5. “Major research project to detect gravitational waves is underway”. University of Birmingham News. University of Birmingham. Archived from the original on December 26, 2018. Retrieved November 28, 2015. ↩

  6. Shoemaker, David (2012). “The evolution of Advanced LIGO” (PDF). LIGO Magazine (1): 8. Archived from the original (PDF) on November 16, 2017. Retrieved November 28, 2015. ↩

  7. “Revolutionary Grassroots Astrophysics Project”Einstein@Home”Goes Live”. Archived from the original on April 9, 2023. Retrieved March 3, 2016. ↩

  8. “LSC/Virgo Census”. myLIGO. Retrieved November 28, 2015. ↩

  9. Castelvecchi, Davide (September 15, 2015), “Hunt for gravitational waves to resume after massive upgrade: LIGO experiment now has better chance of detecting ripples in space-time”, Nature, 525 (7569): 301–302, Bibcode:2015Natur.525..301C, doi:10.1038/525301a, PMID 26381963 ↩

  10. “BOINCstats project statistics”. Archived from the original on October 1, 2012. Retrieved December 14, 2016. ↩

  11. Larger physics projects in the United States, such as Fermilab, have traditionally been funded by the Department of Energy. ↩

  12. “LIGO: The Search for Gravitational Waves”. www.nsf.gov. National Science Foundation. Archived from the original on September 15, 2016. Retrieved September 3, 2018. ↩

  13. “The Nobel Prize in Physics 2017”. Nobel Foundation. Archived from the original on August 13, 2018. Retrieved October 6, 2017. ↩

  14. “LSC News”. ↩ ↩2 ↩3

  15. The LIGO Scientific Collaboration; the Virgo Collaboration; Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abraham, S.; Acernese, F.; Ackley, K.; Adams, C.; Adhikari, R. X.; Adya, V. B. (September 4, 2019). “GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs”. Physical Review X. 9 (3) 031040. arXiv:1811.12907. Bibcode:2019PhRvX…9c1040A. doi:10.1103/PhysRevX.9.031040. ISSN 2160-3308. S2CID 119366083. ↩

  16. LIGO (November 1, 2019). “Welcome to O3b!”. @ligo. Archived from the original on November 1, 2019. Retrieved November 11, 2019. ↩

  17. “LIGO Suspends Third Observing Run (O3)”. March 26, 2020. Archived from the original on April 7, 2023. Retrieved July 15, 2020. ↩

  18. “LIGO-Virgo-KAGRA Collaboration successfully wraps up its fourth Observing Run – LSC – LIGO Scientific Collaboration”. Archived from the original on November 28, 2025. Retrieved July 13, 2026. ↩

  19. “Gravitational-Wave Observatory Status”. Gravitational Wave Open Science Center. May 24, 2023. Retrieved May 25, 2023. ↩

  20. Castelvecchi, Davide (May 24, 2023). “Gravitational-wave detector LIGO is back — and can now spot more colliding black holes than ever”. Nature. 618 (7963): 13–14. Bibcode:2023Natur.618…13C. doi:10.1038/d41586-023-01732-4. PMID 37225822. S2CID 258899900. Archived from the original on May 25, 2023. Retrieved May 25, 2023. ↩

  21. “LIGO, VIRGO AND KAGRA OBSERVING RUN PLANS”. Archived from the original on December 14, 2021. Retrieved December 14, 2021. ↩