Continuous gravitational waves in the laboratory
Gravitational waves are ripples in spacetime created by distant astronomical objects and detected by large, complex detectors (like LIGO, Virgo, and KAGRA). Finding gravitational wave signals in detector data is a complicated task requiring advanced signal processing techniques and supercomputing resources. Because of this complexity, it is difficult to explain gravitational wave research in the undergraduate laboratory, especially because a live demonstration using a gravitational wave detector or a supercomputer is not possible. Through simplification and analogy, tabletop demonstrations are effective in explaining such research and techniques.
A team of OzGrav scientists, from multiple institutions and disciplines, designed a tabletop demo with sample data analysis to explain gravitational wave searches and signal processing techniques. The demonstration may be used as a teaching aid in undergraduate physics and engineering laboratories and should be published in the American Journal of Physics.
Project lead author James Gardner (who was an OzGrav undergraduate student at the University of Melbourne during the project and now a postgraduate researcher at the University Australian National University) explains, “This demonstration offers charming insights into a real-world research field that students like me should appreciate for its recency relative to the age of most of the ideas they come across.”
Tabletop Gravitational Wave Demonstrations
Gravitational wave detectors are very complicated and huge – laser light is sent through tubes several kilometers long! But the operation of a gravitational wave detector can be demonstrated using tabletop equipment. Researchers at the University of Adelaide developed AMIGO to do just that! Deeksha Beniwal, co-author of this study and OzGrav PhD student at the University of Adelaide, explains: “With AMIGO, the portable interferometer, we can easily share how LIGO uses the fundamental properties of light to detect ripples from the far reaches of the universe.
This work develops the demonstration of the portable interferometer with a selection of examples for students of physics and electrical engineering. Changrong Liu, co-author of this study and an OzGrav PhD student in electrical engineering at the University of Melbourne, explains: “This project provides a great opportunity for electrical engineering students like me to put some of their knowledge into the real physical realm and exciting. world.”
Explain Continuous Gravitational Wave Hunting
To demonstrate finding signals with the table setup, the team first had to create fake signals to find! This is where the analogy of sound comes in: audio signals are used to imitate gravitational waves interacting with the detector. The team focused on demonstrating the hunt for continuous gravitational wavesa type of gravitational wave that has yet to be detected.
Hannah Middleton, study co-author and OzGrav associate researcher (at University of Birmingham), explains: “Continuous waves are long-lasting signals from rotating neutron stars. These signals should always be present in the detector data, but the challenge is to find them. This demonstration is directly inspired by the techniques developed by the physicists and electrical engineers of OzGrav in the hunt for continuous gravitational waves!“
A continuous wave signal can change frequency slowly, so the audio signals used in this demonstration also change frequency. “We show, using sound as an analog of gravitational waves, what it takes to detect a wandering tone: a long signal that slowly changes pitch like a whale’s song,” says Gardner.
Professor Andrew Melatos, co-author of this study and leader of the OzGrav-Melbourne node, explains: “We hope that undergraduate teachers will emphasize the interdisciplinary spirit of the project and use it as an opportunity to speak more broadly to students of careers at the intersection of physics and engineering. The future is very bright career-wise for students with experience of interdisciplinary collaboration”
Written by OzGrav Assoc. Researcher Hannah Middleton (University of Birmingham) and OzGrav postgraduate researcher James Gardner (ANU).
Reference: “Continuous Gravitational Waves in the Laboratory: Retrieving Audio Signals with a Benchtop Optical Microphone” by James W. Gardner, Hannah Middleton, Changrong Liu, Andrew Melatos, Robin Evans, William Moran, Deeksha Beniwal, Huy Tuong Cao, Craig Ingram , Daniel Brown and Sebastian Ng, March 23, 2022, American Journal of Physics.