About the KAGRA Project
KAGRA is Japan’s large underground gravitational-wave observatory. It is located about 200 meters below ground inside the Kamioka Mine in Hida City, Gifu Prefecture. The detector has an L-shaped design, with two 3‑kilometer-long arms.
Gravitational waves are tiny “ripples” in space and time that were predicted by Einstein. They are created when very heavy objects like black holes accelerate or collide, and they travel across the universe at the speed of light. When a gravitational wave passes by Earth, space itself stretches and shrinks slightly. The effect is extremely small, so special techniques are needed to reduce noise and measure these tiny changes.
For many years, scientists believed detecting gravitational waves would be extremely difficult. But on September 14, 2015, the two LIGO detectors in the United States made the first-ever observation of gravitational waves from two merging black holes. Later, the Virgo detector in Europe also joined the observations. So far, scientists have observed gravitational waves from the mergers of black hole pairs, neutron star pairs, and neutron star–black hole pairs.
KAGRA reduces noise by being built underground, where the ground is more stable. It also cools its mirrors to very low temperatures to reduce heat-related noise. The project began in 2010, and after years of tunnel and detector construction, KAGRA carried out its first international observing run in April 2020. After improvements during the COVID-19 pandemic, it performed a joint observing run with LIGO from May to June 2023. Although part of the facility was damaged by the Noto Peninsula Earthquake on January 1, 2024, repairs were completed, and KAGRA conducted further observing run with LIGO and Virgo from June to November 2025.
Gravitational-wave astronomy can reveal parts of the universe that cannot be seen with light, radio waves, X-rays, or other traditional methods. With only detectors in the United States and Europe, it is difficult to determine exactly where gravitational waves come from. When KAGRA joins the network, the accuracy of locating gravitational-wave sources improves. Sharing this information with other telescopes allows many observatories to look at the same event at the same time, greatly increasing the scientific discoveries that can be made.
Messages from the KAGRA project leader
The Large-Scale Cryogenic Gravitational Wave Telescope, KAGRA, is a project aimed at observing the “gravitational waves” predicted by Albert Einstein and using them to advance our understanding of the universe.
The project is led by the Institute for Cosmic Ray Research (ICRR) of the University of Tokyo, in collaboration with the High Energy Accelerator Research Organization (KEK) and the National Astronomical Observatory of Japan (NAOJ), with the support of many universities and research institutes in Japan and abroad.
According to Einstein’s theory of general relativity, the presence of massive objects distorts space-time, and when such objects move, the distortion propagates through the universe at the speed of light. These ripples are known as gravitational waves.
Gravitational waves are extremely faint, and researchers around the world have spent many years pursuing ways to detect them. On September 14, 2015, the two gravitational wave observatories of LIGO in the United States succeeded in detecting gravitational waves from the merger of a binary black hole system—the first such observation in human history. This remarkable achievement opened the era of gravitational-wave astronomy.
In the past, astronomy has been based primarily on observations using electromagnetic waves such as visible light, infrared, ultraviolet, radio waves, X-rays, and gamma rays. Because gravitational waves have properties entirely different from electromagnetic waves, they are expected to reveal aspects of the universe that cannot be seen with traditional observational methods. In this sense, a new “window” to the cosmos has been opened.
However, gravitational-wave astronomy has only just begun. To observe a greater number of gravitational waves with higher precision, multiple high-performance gravitational wave detectors around the world are essential. International collaboration, improved detector performance, and stable long-term operation are also indispensable.
Detectors comparable in scale to KAGRA currently exist in the United States and Europe. Japan’s KAGRA, together with these facilities, is expected to play a key and indispensable role in the global gravitational-wave observation network.
Through KAGRA’s observations, we hope to become, together with all of you, witnesses to the new universe that gravitational waves will reveal.
Distinguished University Professor Takaaki Kajita
The Institute for Cosmic Ray Research
Scenes from the KAGRA construction site
Donor Appreciation
To express our gratitude, your donation of over 100,000 yen will be recognized with a permanent personalized nameplate on a plaque near the laboratory entrance of the KAGRA gravitational wave telescope.
KAGRA Observatory website
