The mass which seems to be necessary to explain the dynamical properties of astronomical objects but which has not yet been observed.
Local observations gives 1-20 The Oort method measure the oscillation period of stars above and below the galactic plane and gives 6 Rotation curves measure the period of mass orbiting the galactic center and give 8-20 . Binary galaxies measure the period of two galaxies orbiting each other, and gives 60-180 Clusters of galaxies measure the period of galaxies orbiting in a cluster and give 300-1000 . This progression of larger values as greater distances leads astronomers to conclude that the majority of mass in the universe is not visible. This dark matter could consist of comets, Jupiters, small rocks, or massive neutrinos.