These hypothetical particles are particularly attractive to researchers because they could also solve another outstanding problem in physics, potentially interacting with neutrons to explain why they can feel magnetic fields but not electric ones.

Some scientists are therefore turning their attention to a newer dark matter candidate called the axion, which would be a millionth or even a billionth the mass of an electron, the Proceedings of the National Academy of Science reported. In recent years, this failure has led some in the field to begin wondering if they've headed on a wild particle chase with no real end. Physicists have built enormous detectors and placed them deep underground to protect them from interfering cosmic rays in efforts to detect WIMPs, but so far no experiment has uncovered evidence for them. These dark matter particles would be electrically neutral, which means they would not interact with electromagnetism, the basis of light, and would therefore remain invisible. Like neutrinos, WIMPs would only interact with two of the four fundamental forces in the universe: Gravity and the nuclear weak force, which mediates the decay of radioactive atomic nuclei. (Neutrinos' exact masses are unknown but they are far lighter than electrons). WIMPs would be more similar to the ghostly neutrino, except it would weigh 10 to 100 times more than a proton. These speculative entities are not found in the Standard Model of particle physics, which describes almost all particles and forces. The reigning candidate for dark matter is called a Weakly Interacting Massive Particle or WIMP. Most modern-day astronomers think dark matter likely consists of subatomic particles with properties that are rather different from more familiar protons and neutrons. Telescope surveys were never able to find enough small compact objects to account for this enormous profusion of material.

What is dark matter made of