000 times more mass than a proton. Another candidate is the axion, a particle ten-trillionth of the mass of an electron. In theory, axions would convert to a particle of
we still know little about what dark matter is. The particles in dark matter must either have a lot of mass, or there must be very many of them. Neutrinos meet all the requirements of dark matter. But there is one big difficulty. They have far too little mass.” ...