Date Time Excess x-rays from neutron stars could lead to discovery of new particle A team of scientists, including a University of Minnesota researcher, have found that mysterious x-rays detected from nearby neutron stars may be the first evidence of axions, hypothetical particles that many physicists believe make up dark matter. If their theory is confirmed, the researchers’ findings could help physicists unravel several mysteries of the universe. Their paper is published in Physical Review Letters, a peer-reviewed academic journal published by the American Physical Society. There are many kinds of particles that make up matter in the universe. The most common are protons, neutrons, and electrons. These particles collide with each other in certain settings, such as inside a star’s core or in particle accelerators built by scientists on Earth. Axions have long been elusive to physicists because they are “weakly interacting,” which means they rarely collide with other particles and instead often pass through them.