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In-construction KAGRA gravitational-wave detector.jpg
Alternative namesKAGRA Edit this on Wikidata
Part ofKamioka Observatory Edit this on Wikidata
Location(s)Hida, Gifu Prefecture, Japan
Coordinates36°24′43″N 137°18′21″E / 36.4119°N 137.3058°E / 36.4119; 137.3058Coordinates: 36°24′43″N 137°18′21″E / 36.4119°N 137.3058°E / 36.4119; 137.3058 Edit this at Wikidata
OrganizationInstitute for Cosmic Ray Research Edit this on Wikidata
Altitude414 m (1,358 ft) Edit this at Wikidata
Telescope stylegravitational-wave observatory Edit this on Wikidata
Length3,000 m (9,842 ft 6 in) Edit this at Wikidata
Websitegwcenter.icrr.u-tokyo.ac.jp/en/,%20https://gwcenter.icrr.u-tokyo.ac.jp/ Edit this at Wikidata
KAGRA is located in Japan
Location of KAGRA
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The Kamioka Gravitational Wave Detector (KAGRA), is a large interferometer designed to detect gravitational waves predicted by the general theory of relativity. KAGRA is a Michelson interferometer that is isolated from external disturbances: its mirrors and instrumentation are suspended and its laser beam operates in a vacuum. The instrument's two arms are three kilometres long and located underground at the Kamioka Observatory which is near the Kamioka section of the city of Hida in Gifu Prefecture, Japan.

KAGRA is a project of the gravitational wave studies group at the Institute for Cosmic Ray Research (ICRR) of the University of Tokyo.[1] It became operational on 25 February 2020, when it began data collection.[2][3] It is Asia's first gravitational wave observatory, the first in the world built underground, and the first whose detector uses cryogenic mirrors. It has an operational sensitivity equal to, or greater than, LIGO and Virgo. [1]

The Kamioka Observatory specializes in the detection of neutrino, dark matter and gravitational waves, and possesses other important instruments, including Super Kamiokande, XMASS and NEWAGE. KAGRA is a laser interferometric gravitational wave detector. It is near the neutrino physics experiments.

The collaboration of LIGO, Virgo, and KAGRA plans to start the next observation run (O4) in mid-December, 2022. KAGRA ended its first observation run on 21 April 2020.[4][5]


It was formerly known as the Large Scale Cryogenic Gravitational Wave Telescope (LCGT). The ICRR was established in 1976 for cosmic ray studies. The LCGT project was approved on 22 June 2010. In January 2012, it was given its new name, KAGRA, deriving the "KA" from its location at the Kamioka mine and "GRA" from gravity and gravitational radiation.[6] The word KAGRA is also a homophonic pun of Kagura (神楽), which is a ritual dance dedicated to Gods in Japanese Shinto shrines. The project is led by Nobelist Takaaki Kajita who had a major role in getting the project funded and constructed.[7] The project was estimated to cost about 200 million US dollars.[8]

Development and construction[edit]

Two prototype detectors were constructed to develop the technologies needed for KAGRA. The first, TAMA 300, was located in Mitaka, Tokyo and operated 1998-2008, demonstrating the feasibility of KAGRA. The second, CLIO, started operating in 2006 underground near the KAGRA site. It was used to develop cryogenic technologies for KAGRA.

The excavation phase of tunnels was started in May 2012 and was completed on 31 March 2014.

The construction of KAGRA was completed 4 October 2019, with the construction taking nine years. However, further technical adjustments were needed before it could start observations.[9] The "baseline" planned cryogenic operation ("bKAGRA") was planned to follow in 2020.[10][11]

Operational history[edit]

After the initial adjustment operations, the first observation run started on 25 February 2020.[2][3] Because of COVID-19, the observation run was ended 21 April 2020.[4]

The first detections were made in collaboration with LIGO and Virgo and were reported 11 November 2021.[12][13]

See also[edit]

  • TAMA300, an early prototype in Japan.
  • CLIO, a current prototype that is developing cryogenic technologies.
  • DECIGO, a proposed Japanese space-based interferometer.


  1. ^ a b Mosher, Dave; McFall-Johnsen, Morgan (5 October 2019). "A powerful experiment that cracked a 100-year-old mystery posed by Einstein just got a huge upgrade". Business Insider. Retrieved 5 October 2019.
  2. ^ a b "KAGRA Gravitational-wave Telescope Starts Observation". KAGRA Observatory. 25 February 2020. Retrieved 25 February 2020.
  3. ^ a b 大型低温重力波望遠鏡KAGRA観測開始 (in Japanese). National Astronomical Observatory of Japan. 25 February 2020. Retrieved 25 February 2020.
  4. ^ a b "Japan's KAGRA searches the sky for gravitational waves".
  5. ^ "LIGO, VIRGO AND KAGRA OBSERVING RUN PLANS". Retrieved 14 December 2021.{{cite web}}: CS1 maint: url-status (link)
  6. ^ "LCGT got new nickname "KAGRA"".
  7. ^ Castelvecchi, Davide (2 January 2019). "Japan' s pioneering detector set to join hunt for gravitational waves". Nature. 565 (7737): 9–10. Bibcode:2019Natur.565....9C. doi:10.1038/d41586-018-07867-z. PMID 30602755.
  8. ^ "FAQ (Under Construction) « KAGRA Large-scale Cryogenic Graviationai wave Telescope Project".
  9. ^ "KAGRA gravitational-wave observatory completes construction".
  10. ^ KAGRA International Workshop. (PDF). Masaki Ando. 21 May 2017.
  11. ^ Conover, Emily (2019-01-18). "A new gravitational wave detector is almost ready to join the search". Science News. Retrieved 2019-01-21.
  12. ^ "LIGO, Virgo, and KAGRA raise their signal score to 90". www.aei.mpg.de. Max Plank Institute for Gravitational Physics. Retrieved 13 November 2021.
  13. ^ The LIGO Scientific Collaboration; et al. (2021-11-17). "GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo During the Second Part of the Third Observing Run". arXiv:2111.03606 [gr-qc].