It can take huge equipment to detect the tiniest things, and that's particularly true when it comes to gravitational waves. The LIGO detector uses 4-km-long (2.5-mi) arms to pick up distortions just a thousandth of the width of a proton. But now, a Northwestern University team is aiming to build a gravitational wave detector small enough to fit on a tabletop, which could detect signals the larger facilities miss.
Gravitational waves are actually ripples in the very fabric of spacetime, caused by cataclysms like stars or black holes colliding. It's believed that these waves are washing over us regularly, and while they were first predicted by Einstein's general theory of relativity over a century ago, they weren't directly detected until 2015 – an achievement that earned the scientists behind it the 2017 Nobel Prize in Physics.
About a dozen of these detections have been made in the years since, using LIGO in the US and Virgo in Italy. These facilities work by beaming laser beams down long tunnels and bouncing them back with mirrors. If gravitational waves happen to pass over the Earth, these beams will be ever-so-slightly distorted, and their origin can be calculated by figuring out which arm was hit first and hardest.
But those facilities cover several acres. A team of physicists and astronomers from Northwestern University have now unveiled plans to shrink the tech down to the size of a tabletop. The Levitated Sensor Detector (LSD) would have arms about 1 m (3.3 ft) long, and use them to detect gravitational waves that are of higher frequency than existing detectors can pick up.
"If you think of gravitational waves like sound waves, the frequency we are trying to capture with levitated sensors is sort of like a dog whistle," says Vicky Kalogera, co-investigator of the LSD project. "Dogs are capable of hearing sound frequencies that the human ear cannot perceive. Similarly, levitated sensors will pick up frequencies that LIGO and Virgo cannot detect."
LIGO and Virgo specialize in detecting gravitational waves with frequencies up to 10 kHz, while LSD is designed to pick up signals with higher frequencies. The LISA detector, which ESA is planning to launch in 2034, aims even lower.
"Just like electromagnetic astronomy has telescopes and gamma-ray detectors and more, the gravitational-wave community is now developing the tools needed to detect events on all parts of the spectrum," says Shane Larson, co-investigator of the project. "LISA will detect the big events; LIGO and Virgo pick up the medium events; and LSD will detect the smallest cosmic events."
Exploring a new part of the spectrum, LSD could help astronomers investigate a different range of celestial objects and events. One of the major mysteries the device could help shed light on is dark matter, by studying two potential culprits – primordial black holes, which are smaller and older than other black holes, and axions, hypothetical particles that may make up the strange stuff.
It's set to take two years for the Northwestern team to build and test the LSD prototype, which will then run for one year.
Source: Northwestern University
