For ten points, name this non-luminous, unobserved substance, believed to make up 90% of matter in a galaxy.
First predicted in the Einstein-de Sitter model of the universe, theoretical evidence for it includes the need for it to exist if the cosmological constant for the expansion of the universe is close to one, the need for it to keep clustered galaxies from drifting apart, and the fact that galaxies rotate faster and more uniformly than expected. For ten points, name this non-luminous, unobserved substance, believed to make up 90% of matter in a galaxy.
First predicted in the Einstein-de Sitter model of the universe, theoretical evidence for it includes the need for it to exist if the cosmological constant for the expansion of the universe is close to one, the need for it to keep clustered galaxies from drifting apart, and the fact that galaxies rotate faster and more uniformly than expected.
{Dark matter}