It turns out that dark matter doesn't actually contain certain axion-like particles. As the hunt for dark matter continues, scientists have ruled out some of these particles as part of dark matter's contents.
Physicists are continuing the struggle to identify more than 80 percent of the matter in the universe, and part of this struggle is finding dark matter. In the past, researchers believed it was possible that dark matter could be made up of extremely light particles that weigh less than a billionth of the mass of the electron. These particles are often called axion-like particles (ALPs). ALPs are hard to find, however, which means that researchers haven't been able to test the different types of ALPs that could be part of dark matter.
In this latest study, the researchers used data from NASA's gamma-ray telescope on the Fermi satellite. This allowed them to look at light from the central galaxy of the Perseu galaxy cluster as they searched for ALPs.
It's actually not possible to detect ALPs directly. However, there is a chance that they transform into ordinary light, and vice versa, when they travel through a magnetic field. In this case, the researchers used the very bright light source of the Perseus galaxy cluster to look for these transformations and detect ALPs.
The observations were sensitive enough to exclude certain types of ALPs that couldn't constitute dark matter. In the end, the researchers found no traces of ALPs that could establish dark matter.
"The ALPs we have been able to exclude could explain a certain amount of dark matter," said Manuel Meyer of Stockholm University, one of the researchers involved in the new study. "What is particularly interesting is that with our analysis we are reaching a sensitivity that we thought could only be obtained with dedicated future experiments on Earth."
The researchers currently plan to continue the search for ALPs with the Fermi telescope. With that said, the new findings do help rule out some particles while also giving scientists a better understanding of ALPs. In addition, they may help future searches for dark matter.
The study was published in the April 22 issue of the journal Physical Review Letters.
