The Kamioka Gravitational Wave Detector in Japan, part of the international gravitational wave network.KAGRA is a gravitational wave detector located in the Kamioka mine in Japan, a facility built deep underground to shield it from seismic noise. It is one of the few detectors in the global network alongside LIGO (USA) and Virgo (Italy), and it is unique in using cryogenic mirrors cooled to 20 Kelvin to reduce thermal noise. Its location in the Northern Hemisphere and its orientation allow for better triangulation of gravitational wave sources when combined with other detectors.
Construction began in 2010, and the detector was initially named LCGT (Large-scale Cryogenic Gravitational wave Telescope). It was renamed KAGRA in 2012, combining 'KA' from Kamioka and 'GRA' from gravitational radiation. It first joined the international network in 2020.
KAGRA is a laser interferometer with arms 3 kilometers long. A laser beam is split and sent down two perpendicular arms, reflected by mirrors, and recombined. A passing gravitational wave stretches one arm and compresses the other, causing a tiny phase difference in the recombined light. The cryogenic cooling of the sapphire mirrors reduces thermal vibrations, while the underground location minimizes seismic and other environmental disturbances, enabling sensitivity to spacetime ripples from events like black hole mergers.
KAGRA contributes to the global gravitational wave observatory network, helping to pinpoint the locations of neutron star and black hole mergers and enabling multi-messenger astronomy with telescopes.
The Kamioka mine is also home to the Super-Kamiokande neutrino detector, making it a unique underground site hosting experiments for both gravitational waves and neutrinos.
















