National Astronomical Observatory of Japan

Large-scale Cryogenic Gravitational Wave Telescope

KAGRA

What is the Large-scale Cryogenic Gravitational Wave Telescope KAGRA?

KAGRA is a large-scale cryogenic gravitational wave telescope constructed underground at the Kamioka Mine in Hida City, Gifu Prefecture, Japan. It features a 3-kilometer-long laser interferometer and is part of a global gravitational wave observation network alongside LIGO (USA) and Virgo (Europe). The telescope is undergoing repeated observation runs and upgrades to enhance global detection capabilities. Hosted by the Institute for Cosmic Ray Research (ICRR), University of Tokyo, with the National Astronomical Observatory of Japan (NAOJ) and the High Energy Accelerator Research Organization (KEK) as co-hosts, KAGRA involves collaboration with numerous universities and research institutions in Japan and abroad.

Large-scale Cryogenic Gravitational Wave Telescope KAGRA

Research

Gravitational waves are ripples propagating through space-time. Unlike optical-infrared telescopes like the Subaru Telescope or radio telescopes like ALMA, which capture electromagnetic waves (oscillations in the electromagnetic field), KAGRA detects gravitational waves—distortions in space-time transmitted as waves. Its detection principle is fundamentally different from that of electromagnetic telescopes.

KAGRA uses a technique called laser interferometry. It detects the stretching and squeezing of space caused by gravitational waves by observing interference patterns between laser beams propagated along perpendicular paths. To increase sensitivity, KAGRA requires not only long baseline arms but also high-power laser sources, large-aperture and ultralow-loss mirrors, and ultrahigh-vacuum equipment. KAGRA incorporates a variety of cutting-edge technologies to achieve these goals. We are preparing to lead the upcoming era of gravitational wave astronomy.

The coalescence of binary neutron stars (BNS) is one of the key sources of gravitational waves. This astrophysical phenomenon can also be observed through electromagnetic signals such as gamma rays, optical light, infrared, and radio waves. KAGRA actively seeks collaboration with observatories beyond gravitational wave detectors, including the Subaru Telescope.

Specifications

LocationKamioka, Hida, Gifu, Japan
DetectorLaser interferometer (Michelson interferometer)
Baseline length3 kilometers
Main Features- A 3-kilometer interferometer arm length
- Stable underground site (200–450 m), optimal for reducing seismic noise
- Mirror temperatures cooled to –250°C to suppress thermal noise
- Sapphire mirrors, chosen for their superior performance at cryogenic temperatures

History

January 20, 2012Commencement Ceremony
May 2012Tunnel excavation begins
March 31, 2014Tunnel excavation completed
March 25, 2016Start of test operations
October 2019LIGO-Virgo-KAGRA (LVK) collaboration agreement concluded
April 2020International joint observation (O3GK) with Germany's GEO600
May 2023Participation in international joint observation (O4a) with LIGO and Virgo
January 2024Operations affected by the Noto Peninsula earthquake disaster
June-October 2025 (planned)Participation in international joint observation (O4c) with LIGO and Virgo