Scientists Detected Gravitational Waves That Could Stem From ‘Dark Matter Particles'

They could be primordial black holes. Or even dark matter.
Brad Bergan
A 3D rendering of a black hole and its gravitational waves.andreausK / iStock

We could be on the cusp of a colossal breakthrough in physics.

A novel kind of gravitational wave detector recorded two unusual events, and they could be primordial black holes or dark matter, according to a recent study published in the journal Physical Review Letters.

Most detectors can't record such high-frequency gravitational waves, and the new ones are unlike any yet observed.

High-frequency gravitational waves could be key to detecting dark matter

Gravitational waves happen when powerful forces create ripples in the fabric of space-time, which Einstein predicted more than a century ago, but were only very recently observed empirically, in 2015. And the initial detection has been followed by dozens more, mainly via LIGO-like facilities capable of identifying gravitational waves at frequencies from 7 kHz and 30 kHz. These are caused by unconscionably powerful events, like when a neutron star slams into a black hole. But physicists have also thought these ripples could propagate at frequencies beyond this range. As of writing, two experiments are hunting for comparatively high-frequency waves that might signify other phenomena in the universe.

And, finally, the first cache of data has revealed two suspicious detections that could point to either primordial black holes, or even a sign of dark matter.

The experiment is managed by the ARC Center for Excellence for Dark Matter Particle Physics (CDM), in addition to the University of Western Australia, and employs an unprecedented kind of gravitational wave detector called a bulk acoustic wave (BAW) resonator. The project implements a quartz crystal disk that vibrates at high frequencies when acoustic waves propagate through its material, creating an electric charge that two adjacent conducting plates detect. Then the signal is carried through a superconducting quantum interference device (SQUID) that amplifies the signal, which is then detected.

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The events might be primordial black holes or dark matter

While complicated, this process is also protected from the outside world's electromagnetic radiation via multiple radiation shields, within which the environment is supercooled to a temperature of nearly absolute zero (which further reduces signal noise). All of this enables the engineering marvel to detect waves at frequencies in the MHz range. The BAW project lasted 153 days, with two different runs during 2019, during which scientists detected two uncommon events. The first one was recorded on May 12, with the other much later, on Nov. 27. Both, however, were recorded at 5 MHz, which is a high frequency.

The mystery lies in identifying the cause of these signals, but the scientists have hypothetical solutions: They might be primordial black holes, born in the maddening chaos immediately following the Big Bang (we're talking milliseconds after the bang), which may have seeded supermassive black holes that came to rest at the center of galaxies throughout the cosmos. High-frequency gravitational waves might stem from one of these primordial black holes, but these have yet to be empirically verified. The other possibility is perhaps more enticing, although similarly has yet to be observed: a cloud of dark matter particles rushing through the instrument.

This "matter" is likely abundant throughout the cosmos, but only interacts with our conventional matter via its potent gravitational influence. But make no mistake, confirming either of these possibilities would mean a colossal breakthrough in modern physics, which means we have to spare ourselves from jumping the gun. Because while dark matter or primordial black holes would constitute a world-historical discovery, it might also be something comparatively boring, like a meteor, or some random atomic process. Time will tell what the scientists just witnessed.