Dark matter is an unidentified type of matter comprising approximately 27% of the mass and energy in the observable universe that is not accounted for by dark energy, baryonic matter (ordinary matter), and neutrinos. The name refers to the fact that it does not emit or interact with electromagnetic radiation, such as light, and is thus invisible to the entire electromagnetic spectrum. Although dark matter has not been directly observed, its existence and properties are inferred from its gravitational effects such as the motions of visible matter, gravitational lensing, its influence on the universe's large-scale structure, and its effects in the cosmic microwave background. Dark matter is transparent to electromagnetic radiation and/or is so dense and small that it fails to absorb or emit enough radiation to be detectable with current imaging technology.
Estimates of masses for galaxies and larger structures via dynamical and general relativistic means are much greater than those based on the mass of the visible "luminous" matter.

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