Axions are hypothetical particles that may be a component of dark matter. One place where they could be found is in the radiation from black holes passing through the magnetic fields of galaxy clusters.
Search for axions
Physicists at the University of Copenhagen say they may have found the key to proving the existence of dark matter. We are talking about axions — particles that no one has ever seen, but for which certain characteristics have already been calculated.
Axions, like other possible candidates for dark matter particles, have been sought for decades. And this is not surprising: dark matter remains mysterious, despite the fact that it makes up most of the mass of the Universe.
One possible source of axions is believed to be supermassive black holes in distant galaxies, which absorb ordinary matter and thereby generate electromagnetic radiation. Somewhere inside it, axions are hiding.
They usually do not interact with the rest of the substance in any way, so they are not visible. However, in the powerful and extensive magnetic fields surrounding galaxy clusters, they can give themselves away.
Study of radiation from distant galaxies
Instead of using a particle accelerator on Earth, such as the one at CERN, researchers turned to space and used it as a kind of giant particle accelerator. In particular, they were looking for electromagnetic radiation emanating from the nuclei of distant and very bright galaxies, each of which has a supermassive black hole at its center.
Next, they observed this radiation as it passed through the enormous magnetic fields found in galaxy clusters, where part of it could hypothetically have been converted into axions. This transformation would leave behind tiny, random fluctuations in the data. But each signal is so weak that it is lost in the background noise of the Universe.
Therefore, researchers have presented a new concept. Instead, they observed a total of 32 supermassive black holes located behind galaxy clusters and then combined the data from their observations.
Random noise or a hint of a new particle?
When researchers studied the data, they were surprised to discover a pattern resembling the signature of the elusive axion. “Usually, the signal from such particles is unpredictable and looks like random noise. But we realized that by combining data from many different sources, we turned all this noise into a clear, recognizable pattern,“ explains Oleg Ruchayskiy, associate professor at the Niels Bohr Institute at the University of Copenhagen and senior author of the article in Nature Astronomy entitled “Constraints on axion-like particles from active galactic nuclei seen through galaxy clusters.”
He adds: “It shows up like a unique step-like pattern that shows what this conversion could look like. We only see it as a hint of a signal in our data, but it is still very tantalizing and exciting. You could call it a cosmic whisper, now loud enough to hear.”
Closer to discovering dark matter
Although the pattern discovered by scientists is not proof of the existence of axions, the research by Ruchayskiy and his colleagues brings us closer to understanding what dark matter is.
“This method has significantly expanded our knowledge of axions. It essentially enabled us to map a large area that we know does not contain the axion, which narrows down the space where it can be found,” says postdoctoral researcher Lidiia Zadorozhna, a Marie Curie fellow at the Niels Bohr Institute, who is one of the lead authors of the new paper.
Although this experiment focused on a specific type of electromagnetic radiation known as gamma rays, this method is also applicable to other types of radiation, such as X-rays. Therefore, this method allows us to go beyond previous experimental boundaries and opens up a new way of studying these immense particles.
According to phys.org
