Remember LIGO – the Laser Interferometer Gravitational-Wave Observatory – that made headlines in 2016 for detecting gravitational waves for the very first time? Now, in 2019, scientists aim to design a gravitational-wave detector much smaller than its predecessor.

While LIGO has arms 4 km long, a team of physicists and astronomers from Northwestern University wish to design a detector that is much smaller – small enough to fit a tabletop. Its working will be different too; LIGO works by using lasers and mirrors to detect interference caused by passing gravitational waves, but in the case of Northwestern’s Levitated Sensor Detector (LSD), the detector will use lasers to suspend a glass bead inside a vacuum chamber, creating an extremely force-sensitive sensor with arms just a meter long.

The Northwestern project will use $1 million from the W. M. Keck Foundation, a U.S. charitable foundation based in Los Angeles, and additional support from the university. After two years of development, the meter-long prototype would operate for a preliminary year and potentially pave the way for a larger detector that could reach 10 meters in length.

In terms of usage, LIGO is used to detect gravitational waves of medium frequency, while LSD will be able to pick up higher frequencies. By picking up higher frequencies, scientists will be able to listen for echoes of the formation of primordial black holes and the activity of theoretical particles called “axions”, both of which are strong contenders for dark matter – matter that constitutes most of the universe, but can only be detected through its gravitational presence.

“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,” said Vicky Kalogera, project co-investigator and director of Center for Interdisciplinary Exploration and Research for Astrophysics (CIERA).

“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,” said Kalogera, who is also the Daniel I. Linzer Distinguished University Professor of Physics and Astronomy and one of the foremost astrophysicists in the LIGO Scientific Collaboration (LSC).

What’s interesting to note is that the development of LSD coincides with the development of another detector targeting frequencies on the opposite end of the spectrum. The European Space Agency plans to launch the Laser Interferometer Space Antenna (LISA), a space-based gravitational-wave detector that spans tens of millions of miles, in the early 2030s.

“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,” project co-investigator Shane Larson said. “LISA will detect the big events; LIGO and Virgo pick up the medium events; and LSD will detect the smallest cosmic events.”


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