64 Scientific American, November 2019Lee Billings is a senior editor for space
and physics at Scientific American.IN BRIEF
Studies of gravitational waves using three observatories are revolutionizing
our understanding of black holes, neutron stars and other astrophysical objects.
A fourth observatory, the Kamioka Gravitational-Wave Detector (KAGRA),
is set to begin operations by the end of 2019.
The first observatory of its kind to be built underground and kept at extreme-
ly low temperatures to increase sensitivity, KAGRA is demonstrating innova-
tions crucial for constructing a new generation of even more advanced gravi-
tational-wave detectors.The forefront of this promising future can be found
in a subterranean complex of darkened tunnels. There
more than 200 meters below Mount Ikenoyama in the
Gifu prefecture of central Japan, an international team
of scientists, engineers and technicians is finishing
almost a decade of steady construction, readying the
Kamioka Gravitational-Wave Detector (KAGRA) to
begin operations by the end of this year. Soon KAGRA
will join the world’s three other active gravitational-
wave detectors—the twin stations of the U.S.-based
Advanced Laser Interferometer Gravitational-Wave
Observatory (LIGO) in Hanford, Wash., and in Living-
ston, La., and the Advanced Virgo facility near Pisa,
Italy. KAGRA’s location in Japan and orientation with
respect to LIGO and Virgo will independently check
and enhance those detectors’ observations, allowing
researchers to better measure the orientations and
spins of merging black holes and neutron stars.
Collectively, this quartet of detectors will reach new
heights of sensitivity and precision, finding fainter grav-
itational-wave events than ever before and pinpointing
their celestial coordinates with unprecedented acuity for
follow-up with conventional telescopes. Here selected
photographs capture some of the final technical prepa-
rations before KAGRA is unleashed on the sky.
To find gravitational waves, KAGRA relies on the
same method used by LIGO and Virgo, a technique
called laser interferometry. In this approach, a laser
beam bounces between mirrors suspended at the ends
of two pipelike vacuum chambers. The chambers are
several kilometers long and oriented perpendicularly
to each other, forming what looks like a giant L. The
laser acts as a measuring stick, revealing when a pass-
ing gravitational wave briefly stretches and shrinks
spacetime, altering the chambers’ lengths (and thus
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