KAGRA

The Kamioka Gravitational Wave Detector (KAGRA) is a large-scale physics experiment designed to detect gravitational waves predicted by the general theory of relativity. It is located underground at the Kamioka Observatory which is near the Kamioka section of the city of Hida in Gifu Prefecture, Japan. KAGRA is a Michelson interferometer with 3-km arm length and is designed to eventually be able to observe gravitational wave signatures from binary neutron star mergers at a distance of up to ~150 Mpc .

KAGRA is operated by the Institute for Cosmic Ray Research (ICRR) of the University of Tokyo, the High Energy Accelerator Research Organization (KEK) and the National Astronomical Observatory of Japan (NAOJ) along with collaborators from a number of other scientific institutions . It is part of the larger LVK collaboration along with LIGO and Virgo.

KAGRA was first conceived in the late 1990s and was formally approved in 2010. Construction was completed in 2019, and it first began observing in 2020 . It is Asia's first gravitational wave observatory, the first in the world built underground, and the first whose detector uses cryogenic mirrors. The cryogenic mirrors reduce the thermal noise, while the underground location significantly reduces the noise from seismic waves on the Earth's surface which dominates the noise of LIGO and Virgo at low frequencies. It is expected to eventually reach an operational sensitivity equal to LIGO and Virgo .

KAGRA participated in the O3 observing run of LIGO and Virgo in 2019 and 2020 and in O4a for a month in 2023 before going back to commissioning. The experiment was damaged in the 2024 Noto earthquake but recovered enough to participate in O4c in 2025 .