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.

Kamioka Gravitational wave detector (KAGRA)
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; 137.3058 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
observatory Edit this on Wikidata
Length3,000 m (9,842 ft 6 in) Edit this at Wikidata
Websitegwcenter.icrr.u-tokyo.ac.jp/en/, gwcenter.icrr.u-tokyo.ac.jp
KAGRA is located in Japan
KAGRA
Location of KAGRA
  Related media on Commons

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 is expected to have an operational sensitivity equal to, or greater than, LIGO and Virgo. [1]

The Kamioka Observatory specializes in the detection of neutrinos, dark matter and gravitational waves, and has 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 started its current observation run (O4) on 24 May 2023.[4] KAGRA ended its first observation run on 21 April 2020.[5][6]

Name edit

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.[7] 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.[8] The project was estimated to cost about 200 million US dollars.[9]

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 detector is housed in a pair of 3 km-long arm tunnels meeting at a 90° angle in the horizontal plane, located more than 200 m underground.[10] 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.[11] The "baseline" planned cryogenic operation ("bKAGRA") was planned to follow in 2020.[12][13]

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.[5] The sensitivity during this run was only 660 kpc (binary neutron star inspiral range).[14] This is less than 1% the sensitivity of LIGO during the same run, and around 10% of KAGRA's expected sensitivity for the run.[15] The sensitivity has reached 1 Mpc and the latest observations (O4) started on 25 May 2023.[16]

Aftermath of 2024 Noto earthquake edit

Due to the 2024 Noto earthquake on 1 January 2024, whose epicenter was about 120 km from KAGRA, it suffered damages in mirror suspension mechanism. As of 5 February 2024, the project is expecting to return to observation in January 2025.[17]

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.

References edit

  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. ^ "Gravitational-wave detectors start next observing run to explore the secrets of the Universe". Max Planck Society. 24 May 2023. Retrieved 8 June 2023.
  5. ^ a b "Japan's KAGRA searches the sky for gravitational waves".
  6. ^ "LIGO, VIRGO AND KAGRA OBSERVING RUN PLANS". Retrieved 11 October 2022.
  7. ^ "LCGT got new nickname "KAGRA"".
  8. ^ 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.
  9. ^ "FAQ (Under Construction) « KAGRA Large-scale Cryogenic Graviationai wave Telescope Project".
  10. ^ Abe, H.; et al. (26 April 2022). "The Current Status and Future Prospects of KAGRA, the Large-Scale Cryogenic GravitationalWave Telescope Built in the Kamioka Underground". Galaxies. 10 (3): 63. Bibcode:2022Galax..10...63A. doi:10.3390/galaxies10030063. hdl:11572/371989.
  11. ^ "KAGRA gravitational-wave observatory completes construction".
  12. ^ KAGRA International Workshop. (PDF). Masaki Ando. 21 May 2017.
  13. ^ Conover, Emily (2019-01-18). "A new gravitational wave detector is almost ready to join the search". Science News. Retrieved 2019-01-21.
  14. ^ Collaboration, KAGRA; et al. (2023). "Performance of the KAGRA detector during the first joint observation with GEO 600 (O3GK)". Progress of Theoretical and Experimental Physics. 2023 (10). arXiv:2203.07011. doi:10.1093/ptep/ptac093.
  15. ^ "Advanced LIGO, Advanced Virgo and KAGRA observing run plans" (PDF). KAGRA Collaboration, LIGO Scientific Collaboration, and Virgo Collaboration. 11 July 2019. Retrieved 11 October 2022.
  16. ^ "KAGRA started O4 observing run at 0:00 JST on May 25th". KAGRA Observatory. 25 May 2023.
  17. ^ 2024年1月1日能登半島地震によるKAGRAの被災状況について (in Japanese). Institute for Cosmic Ray Research, University of Tokyo. 5 February 2024. Retrieved 5 February 2024.

External edit