Underground Detector in Japan to Join Search for Gravitational Waves

An illustration of the underground KAGRA detector.
An illustration of the underground KAGRA detector.
Illustration: ICRR, Univ. of Tokyo.

A fourth gravitational wave detector, this one in Gifu Prefecture, Japan, will join the global search for cosmic events that cause ripples in spacetime, beginning this December.


The Kamioka Gravitational-Wave Detector (KAGRA) is in its commissioning phase, according to a press release, and will join the two LIGO detectors in the United States well as the Virgo detector in Italy. The three facilities will share data, serving as independent verifiers of each other’s results.

Like the LIGO and Virgo detectors, KAGRA uses laser interferometry to search for tiny ripples in spacetime called gravitational waves. The experiment consists of a pair of 1.9-mile-long arms buried underground. Optics split a laser beam and send it through either side of the tunnel, then rejoin the beam on the detector. A gravitational wave will cause the beams to move in and out of alignment with one another, generating a tell-tale wiggle signal.

KAGRA is the first of the major gravitational detectors to operate underground, making it less susceptible to outside noise that can produce erroneous signals. It will also be the first with cryogenically cooled mirrors, which will cut down on noise caused by heat-related effects, according to the LIGO press release.

The two LIGO gravitational wave detectors first announced discovering gravitational waves in 2015—the result of two black holes tens of times the mass of the Sun colliding and releasing energy, 1.3 billion light-years away. The Virgo detector joined and provided an independent confirmation of the signals, and in 2017, the detectors further observed a signal consistent with the collision of a pair of neutron stars—small, incredibly dense stellar corpses. Three of LIGO’s founders received the 2017 Nobel Prize for their work.

But a fourth gravitational detector will be an important addition. It provides an independent verification for LIGO’s detections, but more importantly, it will help further localize the origin of these gravitational waves in the sky. Part of the excitement surrounding this new astronomy is the ability to detect gravitational waves and then use conventional telescopes to search for what might have caused the ripples. Astronomers haven’t spotted any of these “multimessenger” sources since 2017. The fourth detector will hopefully increase the precision on the location of the gravitational waves’ origins, giving astronomers smaller regions of the sky to search with telescopes

Construction on KAGRA finished this past spring, and today, LIGO, Virgo, and KAGRA scientists signed a memorandum of agreement detailing their collaborative efforts and how they will share data. The other three detectors have been operating since April 1 of this year, and beginning in December, all four observatories will run until April of next year.


Former Gizmodo physics writer and founder of Birdmodo, now a science communicator specializing in quantum computing and birds


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