Even the strongest gravitational waves that pass through the planet, created by the distant collisions of black holes, only stretch and compress each mile of Earth’s surface by one-thousandth the diameter of an atom. It’s hard to conceive of how small these ripples in the fabric of space-time are, let alone detect them. But in 2016, after physicists spent decades building and fine-tuning an instrument called the Laser Interferometer Gravitational-Wave Observatory (LIGO), they got one.
With nearly 100 gravitational waves now recorded, the landscape of invisible black holes is unfurling. But that’s only part of the story.
Gravitational wave detectors are picking up some side gigs.
“People have started to ask: ‘Maybe there’s more to what we get out of these machines than just gravitational waves?’” said Rana Adhikari, a physicist at the California Institute of Technology.
Inspired by the extreme sensitivity of these detectors, researchers are devising ways to use them to search for other elusive phenomena: above all, dark matter, the nonluminous stuff that holds galaxies together.
In December, a team led by Hartmut Grote of Cardiff University reported in Nature that they had used a gravitational wave detector to look for scalar-field dark matter, a lesser-known candidate for the missing mass in and around galaxies. The team didn’t find a signal, ruling out a large class of scalar-field dark matter models. Now the stuff can only exist if it affects normal matter very weakly — at least a million times more weakly than was previously thought possible.
“It’s a very nice result,” said Keith Riles, a gravitational wave astronomer at the University of Michigan who wasn’t involved in the research.
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