Scientists explain some of the finer points of the KAGRA gravitational wave detector housed in an underground tunnel in Hida, Gifu Prefecture. (Video footage by Shuhei Yamashita)

Photo/Illutration Laser beams pass through this vacuum pipe that measures 3 kilometers in length. (Shuhei Yamashita)

A ceremony was held Oct. 4 in Gifu Prefecture to mark the completion of the KAGRA gravitational wave detector that scientists hope will play a key role in detecting gravitational waves generated by catastrophic cosmic events, such as the birth of a black hole.

The KAGRA in Hida city will be the fourth of its kind in the world. A network of detectors located in distant locations is needed to simultaneously detect gravitational waves to determine their source.

The KAGRA will be operated by the University of Tokyo's Institute for Cosmic Ray Research, headed by Takaaki Kajita, the 2015 co-recipient of the Nobel Prize in Physics.

Observations at the KAGRA facility are expected to begin before the end of the year.

The central experiment room is located underground at the former site of the Kamioka mine, which also contains the Super-Kamiokande neutrino detector.

Kajita won his Nobel Prize for his discovery of oscillations in atmospheric neutrinos, which indicated that subatomic particles have mass. The Super-Kamiokande played a key role in that discovery.

At the Oct. 4 ceremony at the KAGRA facility, Kajita said it would serve as the Asian base for the international detection network.

"This is the result of nine years of work to complete the facility and it will be used to produce results in science research," Kajita said.

Albert Einstein predicted the existence of gravitational waves in his theory of relativity published in 1916. Direct observation of the wave would have to await a century, but it also led to the awarding of the Nobel Prize in Physics in 2017.

The KAGRA has an accuracy that allows it to observe any change in a single hydrogen atom from a distance equivalent to that separating Earth from the sun.

The detector is made up of an L-shaped vacuum pipe with each side measuring 3 kilometers. Laser beams will be projected into the pipe to detect gravitational waves. Scientists hope to take advantage of some features of the KAGRA to gradually improve its functions to match those of the other three detectors already in operation.

Agreements were signed on Oct. 4 for cooperative efforts between the KAGRA facility and the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Washington state and Louisiana as well as the Virgo interferometer located near Pisa, Italy.

(This article was compiled from reports by Mariko Takahashi and Tomoki Tajima.)