Axions in Pulsars
Has Dark Matter been converted to X-rays in Neutron Star magnetic fields?
Many people have heard of neutrinos (little ‘neutral ones’). They are produced in abundance in the Sun, come in three flavors (electron, muon, and tau) and have no charge, and very small masses. The upper limit of the combined masses of the three flavors is 0.12 eV.
There is a hypothesized particle known as the sterile neutrino that is a candidate for dark matter, but these would be heavier, extremely so, probably much more than a proton mass.