Dark matter isn’t made of certain axion-like particles

A team of researchers has ruled some axion-like particles out as the dark matter’s content. Physicists are still struggling with the conundrum of identifying more than 80 percent of the matter in the Universe. One possibility is that it is made up by extremely light particles which weigh less than a billionth of the mass of the electron.

These particles are often called axion-like particles (ALPs). Since ALPs are hard to find, the researchers have not yet been able to test different types of ALPs that could be a part of the dark matter.

For the first time the Stockholm University researchers used data from NASA’s gamma-ray telescope on the Fermi satellite to study light from the central galaxy of the Perseus galaxy cluster in the hunt for ALPs.

The researchers found no traces of ALPs and, for the first time, the observations were sensitive enough to exclude certain types of ALPs (ALPs can only constitute dark matter if they have certain characteristics).

“The ALPs we have been able to exclude could explain a certain amount of dark matter. 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”, says researcher Manuel Meyer.

Searches for ALPs with the Fermi telescope will continue. More than 80 percent of the matter in the Universe remains to identify. The mysterious dark matter shows itself only through its gravity, it does neither absorb nor radiate any form of light.

The article is now published in the Physical Review Letters.