Physics

Japanese gravitational wave detector to join LIGO and Virgo

Japanese gravitational wave de...
A rendering of the upcoming KAGRA gravitational wave detector in Japan, which is being built underground
A rendering of the upcoming KAGRA gravitational wave detector in Japan, which is being built underground
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A rendering of the upcoming KAGRA gravitational wave detector in Japan, which is being built underground
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A rendering of the upcoming KAGRA gravitational wave detector in Japan, which is being built underground
The four gravitational wave facilities, LIGO Hanford (top left), KAGRA (top right), Virgo (bottom left) and LIGO Livingston (bottom right)
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The four gravitational wave facilities, LIGO Hanford (top left), KAGRA (top right), Virgo (bottom left) and LIGO Livingston (bottom right)

Later this year a new detector is set to begin hunting for gravitational waves – ripples in the very fabric of spacetime. The Kamioka Gravitational-wave Detector (KAGRA) in Japan will join the Laser Interferometer Gravitational-wave Observatory (LIGO) in the US and Virgo in Italy, and together the three observatories will be better able to triangulate where any waves are coming from.

It takes a tremendous amount of energy to distort spacetime itself, but collisions between massive objects like black holes and neutron stars can do the trick. Over a century ago, Einstein himself predicted that such events would produce ripples he called gravitational waves, but they weren’t detected directly until 2015.

In the few years since, these waves have been detected washing over the Earth more than 30 times. The first few detections were made by LIGO, which is made up of two facilities in the US – one in Washington and the other in Louisiana. In 2017, Virgo tagged in to help, and its position in Italy allowed scientists to more precisely narrow down where the waves were coming from.

One of the most impressive feats came later in 2017, when the three facilities confined a detection to a patch of about 0.1 percent of the sky. That told astronomers where to point other telescopes and observatories, and allowed them to spot the visual fireworks of two neutron stars smashing together.

And now a fourth location is due to come online by the end of the year. KAGRA will work closely with LIGO and Virgo, and thanks to its point of view in Japan, the newly extended network will be able to zero in on a signal three times more precisely than before.

The four gravitational wave facilities, LIGO Hanford (top left), KAGRA (top right), Virgo (bottom left) and LIGO Livingston (bottom right)
The four gravitational wave facilities, LIGO Hanford (top left), KAGRA (top right), Virgo (bottom left) and LIGO Livingston (bottom right)

KAGRA will also be bringing a few new tricks to the table, helping to cut down on interference. It will be the first gravitational wave observatory of this size to operate underground, which will reduce interference from wind and seismic activity. And its mirrors will be cryogenically chilled, which helps to cut down on interference from heat.

"These features could supply a very important direction for the future of gravitational-wave detectors with much higher sensitivities,” says Takaaki Kajita, the principal investigator of the KAGRA project. “Therefore, we should make every effort, for the global gravitational-wave community, to prove that the underground site and the cryogenic mirrors are useful.”

When it first fires up in December, KAGRA will be operating at frequencies that are most likely too low for it to make any gravitational wave detections. But it’s expected that it will become more sensitive over time, as its instruments improve, and should eventually be able to join the hunt proper.

Source: Caltech

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