By Davide Castelvecchi
Inside a house-sized scaffolding wrapped in thick plastic sheets, Takayuki Tomaru is in full clean-room attire. The physicist is performing one of the most delicate and crucial tasks in the construction of a gravitational-wave observatory: installing one of the machine’s four mirrors, each a 23-kilogram cylinder of solid sapphire known as a test mass. When operations begin later this year, their job will be to bounce infrared-laser beams back and forth along two 3-kilometre high-vacuum pipes, ready to sense the passage of gravitational waves.
The ¥16.4-billion (US$148-million) observatory — Japan’s Kamioka Gravitational Wave Detector (KAGRA) — will work on the same principle as the two detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States and the Virgo solo machine in Italy. In the past few years, these machines have begun to detect gravitational waves — long-sought ripples in the fabric of space-time created by cataclysmic cosmic events such as the merging of two black holes or the collision of two neutron stars.
With the addition of KAGRA, the growing global network of detectors will enable astrophysicists to locate the position of these feeble cosmic signals in the sky with greatly increased precision. They will be able to dissect the waves’ properties, such as how they are oriented in space, better than ever before, ultimately allowing them to learn more about the elusive cosmic objects that produce them.
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