This Tabletop Gravitational Wave Detector Could Shed Light on Dark Matter

When the first detection of a gravitational wave was announced in 2016, the achievement was immediately recognized as a major scientific milestone, and it ultimately earned the 2017 Nobel Prize in Physics.

Though gravitational waves—ripples in the fabric of spacetime—were theorized about for a century, directly detecting them required the construction of the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Italian Virgo detector. These facilities “hear” vibrations created by disruptive cosmic events using laser tripwires in tunnels that measure up to 2.5 miles in length.

Now, scientists at Northwestern University are developing a scaled-down version of these enormous observatories that could fit on a tabletop. The concept, which is called a Levitated Sensor Detector (LSD), is designed to pick up gravitational waves with frequencies greater than 10 kHz, which have never been heard before.

The W. M. Keck Foundation awarded $1 million to the Northwestern team to build an LSD prototype of the detector over the next two years, according to a statement on Tuesday.

“The size [of LSD] is scaled down by a factor of 4,000 [compared to LIGO], but it is fundamentally different in the way it operates,” Andrew Geraci, principal investigator of LSD, said in an email.

LIGO and LSD both have two armlike cavities that form the shape of an L. LIGO captures gravitational waves by monitoring subtle changes in the distances traveled by lasers as they bounce off mirrors at opposite ends of these cavities. LSD, meanwhile, will pick up waves when they disturb particles levitated by the radiation pressure within the detector’s short one-meter arms.

European scientists are also working on a space-based detector called the Laser Interferometer Space Antenna (LISA), composed of three spacecraft located 1,500,000 miles from each other. If launched as planned in the 2030s, LISA would listen to low frequencies ranging from 0.1 mHz to 1 Hz, a range that includes the gargantuan rumbles made by collisions between supermassive black holes.

LSD is designed to pick up the vibrations emitted by smaller wave-makers, such as primordial black holes located in the early universe. The detector may also confirm the existence of axions, a hypothesized type of particle that is predicted to be a component of dark matter.

“Dark matter is one of the biggest puzzles in physics and astronomy,” Geraci explained. “There is about five times as much of it in the universe as there is ordinary matter, yet we don't know what it is made of, and so far we have only observed how it interacts through its gravitational pull on ordinary matter.”

“If we can detect gravitational signals from either primordial black holes or from axion clouds around nearby black holes it would be a huge clue towards helping us understand the composition of (at least part of) the dark matter,” he said.

Gravitational wave astronomy was born just a little over three years ago, but scientists are already developing new ways to vastly extend the range of frequencies we can detect in the universe. LIGO and its partners first opened our ears to these new phenomena, but fortunately it looks as if they will be far from the last detectors to tune in.