Scientists may be closing in on solving the mystery of dark matter, a hypothetical, nonluminous material that is believed to comprise a large majority of the mass in our universe, in new research that may link it to the existence of a hypothetical subatomic particle.
Among the primary questions scientists have about dark matter is what it could be made of. However, new research by an international team of astrophysicists proposes a possible candidate, meaning that this elusive cosmic material might be detectable in the form of a glow emanating from certain kinds of stars.
The research, conducted by astrophysicists at the universities of Amsterdam and Princeton, suggests that dark matter, which presently is believed to constitute around 85% of the matter in the universe, could be composed of hypothetical particles known as axions.
First proposed in the 1970s to resolve an unrelated problem involving neutrons, axions are of interest to dark matter researchers because if they possess a low mass within a certain range, they could be good candidates in the search for dark matter. Not only that, but they might help to potentially explain how and why dark matter has remained so elusive.
Axions are thought to weakly interact with known particles, which, like dark matter, makes them difficult to detect. That isn’t to say that scientists don’t have a good idea about where to look, since according to the recent findings, axions may be able to be converted into light in the presence of strong electromagnetic fields, thereby illuminating these invisible universal mysteries.
If this is correct, one of the best places to begin any search for axions—and potentially also for dark matter—is to look where the strongest magnetic fields in the universe are known to occur.
Astrophysicists are aware that regions around rotating neutron stars, otherwise known as pulsars, are prime candidates for the search. Possessing a mass comparable to our Sun, but packed into a space close to 100,000 times smaller, pulsars spin very rapidy and produce bright radio emissions along their rotational axis, thereby generating a powerful electromagnetic field.
If axions exist, then the powerful magnetic fields of pulsars make them the perfect place to search for them.
In their recent research, the international team of physicists and astronomers developed a theoretical framework that helped them understand how axions might be produced in these stellar regions, as well as how they might be converted into radio waves emitted by the rotation of pulsars.
Using computer simulations, the team was able to successfully model axion production around pulsars and predict the resulting additional radio signal that would be likely to indicate the presence of the otherwise invisible axions.
With this information, the team then used observations from 27 nearby pulsars, comparing their models to these real-life sources of cosmic radio waves. Despite their best attempts, however, the team was unable to find any conclusive evidence yet that points to the existence of the elusive axions.
Nonetheless, the team feels that the absence of being able to confirm the existence of axions is an intriguing finding, given that their simulations allowed them to place the strongest limits yet produced on the interactions axions are likely to be able to have with light.
“The limits presented here are the strongest to date for axion masses,” the team wrote in a recent paper detailing their research, “and crucially do not rely on the assumption that axions are dark matter.”
Going forward, they hope that additional modeling could help to finally resolve these questions, with the team’s research marking the beginning of what could represent a new interdisciplinary field that aims to learn whether these mysterious hypothetical subatomic particles exist, and of course, whether they might still be related somehow to the search for the universe’s ever-elusive dark matter.
The team’s study, “Novel Constraints on Axions Produced in Pulsar Polar-Cap Cascades,” was written by authors Dion Noordhuis, Anirudh Prabhu, Samuel J. Witte, Alexander Y. Chen, Fábio Cruz and Christoph Weniger, and was published in Physical Review Letters.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email at micah@thedebrief.org. Follow his work at micahhanks.com and on X: @MicahHanks.