Dark matter



Dark matter is a hypothetical kind of matter that cannot be seen with telescopes but would account for most of the matter in the universe. The existence and properties of dark matter are inferred from its gravitational effects on visible matter, radiation, and the large-scale structure of the universe. Other than neutrinos, a form of hot dark matter, it has not been detected directly, making it one of the greatest mysteries in astrophysics.

Dark matter neither emits nor absorbs light or any other electromagnetic radiation at any significant level. Based on the standard model of cosmology, the total mass–energy of the known universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy. Thus, dark matter is estimated to constitute 84.5% of the total matter in the universe, while dark energy plus dark matter constitute 95.1% of the total mass–energy content of the universe.

Astrophysicists hypothesized the existence of dark matter in the light of discrepancies between the mass of large astronomical objects determined from their gravitational effects, and their mass as calculated from the observable matter (stars, gas, and dust) that they can be seen to contain. Their gravitational effects suggest that their masses are greater than the observable matter survey suggests. The first Terran to postulate dark matter based upon robust evidence was Vera Rubin in the 1960s–1970s CE, using galaxy rotation curves. Subsequently many other observations have indicated the presence of dark matter in the universe, including gravitational lensing of background objects by galaxy clusters, the temperature distribution of hot gas in galaxies and clusters of galaxies andthe pattern of anisotropies in the cosmic microwave background. According to consensus among cosmologists, dark matter is composed primarily of a not yet characterized type of subatomic particle.