Scientists have developed a new way of searching for elusive dark matter, which makes up 85% of all matter in the Universe, using detectors that are meant to observe gravitational waves.
The researchers, who were looking for a specific ultra-low-mass form of dark matter, reached a factor 10,000 improvement over previous world-leading results using Laser Interferometer Gravitational-Wave Observatory (LIGO) data from 2019-2020.
The first-of-its-kind analysis, led by scientists at Cardiff University, targeted subtle changes in the instrument's mirrors made by dark matter and possible only because of LIGO's unrivalled precision in detecting changes smaller than the diameter of an atomic nucleus.
Their findings, published in Physical Review Letters, put new limits on the strength of ultra-low-mass dark matter, which the team says can be improved upon further with new detector data.
Professor Hartmut Grote of Cardiff University's School of Physics and Astronomy and the instigator of the study said: "The dark matter problem – observing unattributed mass in the Universe – is probably the biggest unsolved mystery in physics and astronomy.
"For more than 50 years researchers have grappled with understanding what this mass is made of, how it was created, and where it came from."
In the past, searches have focussed on relatively heavy particles, but with the help of studies like ours, they are shifting towards lighter ones where gravitational-wave detectors such as LIGO, Virgo and KAGRA excel.
Gravitational wave detectors consist of kilometre-long, L-shaped vacuum tubes through which a laser beam is bounced back and forth between mirrors, placed at opposite ends of each arm.
Scientists search for signs of a gravitational wave entering the detectors by looking for a tiny mismatch in the time it takes each laser beam to complete its journey.
Lead author Dr Alexandre Göttel from Cardiff University's School of Physics and Astronomy, said: "We can think of LIGO detections in the same way as detecting sounds."
In this context, our improvement is like an 80dB boost in sensitivity-imagine standing in the front row of a rock concert and being able to hear a whisper.
This "whisper" refers to a new interaction between dark matter and some of the mirrors in LIGO, identified by the Cardiff team.
To extract more information about what exactly the detector was measuring, the researchers developed detailed simulations of these complex and frequency-dependent interactions between dark matter and the laser beams.
A new calculation method was also created to process their results at a greater scale.
Dr Göttel added: "If dark matter was made up of heavy particles as originally expected, it would probably have been found by now. Wave-like theories of dark matter have been shown to explain all observed phenomena and are a strong alternative candidate.
"Our method enables the inclusion of significantly more data in our analyses, unlocking the full potential of future gravitational-wave detectors and positioning them at the forefront of ultra-low-mass dark matter searches now and in the future.
"This is even more exciting when you consider that we used relatively "old" data from 2019-2020, meaning our results will improve even more with newer data currently being recorded by LIGO."
The team is currently working on including more LIGO data in their calculations, which they believe will be able to further surpass current limits on ultra-low-mass dark matter.
Dr Vivien Raymond, another of the paper's authors and also from Cardiff University's School of Physics and Astronomy, said: "It's fascinating how gravitational-wave observatories, which were designed to study events billions of light-years away, provide such precise measurements that we could repurpose their data to look for the effect of dark matter on the mirrors themselves."
Our study demonstrates that in addition to observing black holes and neutron stars well beyond our Galaxy, we can use those same instruments for laboratory physics experiments on dark matter.
Gravity Exploration Institute
The paper, 'Searching for scalar field dark matter with LIGO', is published in Physical Review Letters.
