KAGRA to Join International Gravitational Wave Project; Underground Facility Recently Improved Instruments

The Yomiuri Shimbun

13:00 JST, February 23, 2025

The Kamioka Gravitational wave detector, Large-scale Cryogenic Gravitational Telescope (KAGRA) is scheduled to join an international scientific observation project for the first time since its establishment, starting in June at the earliest.

KAGRA, located in Hida, Gifu Prefecture, is operated by entities including the University of Tokyo’s Institute for Cosmic Ray Research. The facility will participate in the project together with counterparts in the United States and European countries.

KAGRA has yet to succeed in detecting gravitational waves since it began operation in 2020. This time, researchers have taken measures to improve KAGRA’s observational sensitivity with the aim of detecting gravitational waves for the first time inside Japan.

Gravitational waves are produced by such incidents as mergers of extremely massive astronomical objects, including black holes.

Researchers in the United States succeeded in detecting gravitational waves for the first time in the world in 2015, and researchers in Europe did so in 2017. The U.S. researchers later received the Nobel Prize in Physics.

Detecting gravitational waves with more than one detector can raise the accuracy of observations. It is expected that scientific understanding of the nature of black holes and other mysteries of the universe will be advanced.

Located 200 meters underground, KAGRA comprises two pipe arms, each measuring 3 kilometers long, combined in an L-shaped structure.

KAGRA aims to detect a phenomenon in which laser beams making round trips inside the pipe arms undergo minute distortions due to the effects of passing gravitational waves.

KAGRA began trying to detect the waves in 2020, making its first attempt with the United States in 2023. But KAGRA could not detect any at the time because its observation devices were insufficiently sensitive.

Researchers at KAGRA aimed to begin observations again in spring 2024, but the plan was postponed because the observation devices were affected by the Noto Peninsula Earthquake on Jan. 1 of that year.

The researchers improvements and decided to join the international project with U.S. and European counterparts beginning as early as June of this year.

The researchers increased KAGRA’s observational sensitivity about seven-fold compared with that before the improvements, through such measures as improving anti-vibration equipment. They aim for the facility have a performance level at which it can observe points in the universe 32.6 million light years from Earth.

Prof. Hideyuki Tagoshi of the institute, an expert on gravitational wave physics, said, “By observing in Japan, the United States and Europe simultaneously, it will be easier to identify the locations of origins of gravitational waves.”