Axion dark matter: Astronomers may finally shed light on the invisible force

What is it and why is it so important?
Chris Young

How do you pinpoint an invisible force?

Scientists from Durham University and Kings College London presented a new theoretical review that strongly supports the search for axion dark matter, a press statement reveals.

It provides a new outline for dark matter detection, as well as a renewed call for scientists to investigate the hypothetical axion particle.

Detecting dark matter

Though dark matter is known to make up 85 percent of the matter in the universe, its exact composition remains a mystery to the scientific community. Scientists know of dark matter due to its observable gravitational effect on stars and galaxies, but they do not know what kind of particle accounts for the mysterious force.

One contender is the axion, a hypothetical elementary particle first postulated in 1977 as part of the Peccei-Quinn theory that provided a possible solution to the strong CP problem. In that theory, the axion explains why the strong interaction — the force that binds quarks in protons and neutrons — obeys time-reversal symmetry. 

"It is a very exciting time to be an axion physicist. Nobody yet knows the identity of dark matter," said study co-author Dr. Francesca Chadha-Day. "By searching for different possibilities, such as the axion, we hope to one day solve this mystery."

Analyzing axions

The researchers behind the new theoretical review analyzed axions from a mathematical perspective and they also posited how the hypothetical particles relate to the fundamental symmetries of the Standard Model of particle physics. "Axion dark matter behaves more like a field covering the universe than like individual particles," the researchers explained in their press statement. "In the early universe, the value of the axion field begins to oscillate back and forth. The energy stored in these oscillations is axion dark matter."

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The new study provides potential methods for how to detect axion interactions in a lab. Though Axion dark matter, in theory, interacts very weakly with light — as does all dark matter — a photon traveling through a magnetic field has a small probability of turning into an axion, the researchers explained. With that in mind, astronomers might hone in on images of galaxies observed shining through magnetic fields. The researchers hope their work helps to provide an outline for new avenues that could eventually lead to the long-sought detection of dark matter.  

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