- a hypothetical form of matter invisible to electromagnetic radiation, postulated to account for gravitational forces observed in the universe.
- astronomy matter known to make up perhaps 90% of the mass of the universe, but not detectable by its absorption or emission of electromagnetic radiation
- Matter that emits little or no detectable radiation. Gravitational forces observed on many astronomical objects suggest the significant presence of such matter in the universe, accounting for approximately 23 percent of the total mass and energy of the universe. Its exact nature is not well understood, but it may be largely composed of varieties of subatomic particles that have not yet been discovered, as well as the mass of black holes and of stars too dim to observe. Also called missing mass
Unseen matter that may make up more than ninety percent of the universe. As the name implies, dark matter does not interact with light or other electromagnetic radiation, so it cannot be seen directly, but it can be detected by measuring its gravitational effects. It is believed that dark matter was instrumental in forming galaxies early in the Big Bang.