A hypothetical form of matter not containing baryons—that is, without protons or neutrons. An example would be the positron–electron ‘atoms’ that may constitute much of the Universe in the very distant future if protons decay. Non-baryonic matter has been suggested as a possible component of the dark matter in the Universe. In this case it could take the form of neutrinos, if they have non-zero rest mass, or of hypothetical particles called WIMPs (weakly interacting massive particles).
Subjects: Astronomy and Astrophysics.