dark matter: a standalone construct

Fritz Zwicky introduced the idea in 1933 when he measured how fast galaxies move within the Coma cluster and found they moved far too quickly to be held together by the mass he could see, so he proposed an unseen gravitating substance he named dunkle Materie, German for dark matter. The modern anchor for the construct is the rotation-curve work of Vera Rubin and Kent Ford, whose 1970 spectroscopic survey of the Andromeda galaxy showed that stars far from the center orbit about as fast as those near it, contrary to what the visible mass alone predicts and pointing to a large halo of matter that gives off no detectable light. Dark matter, then, is a hypothesized form of matter that does not emit, absorb, or reflect light at any wavelength, so it cannot be seen directly, and whose presence is inferred only from its gravitational pull on ordinary matter and on light itself. What makes it a landmark in physical science is its reach: the same unseen mass is called on to explain galactic rotation curves, the bending of light in gravitational lensing, the growth of large-scale cosmic structure, and the pattern of the cosmic microwave background, and current cosmological accounting attributes far more of the universe's matter to it than to the ordinary matter of stars, gas, and planets. The word also appears colloquially as a metaphor for anything hidden yet influential, a usage kept separate from the physical construct defined here.[1][2][3]

Unit

A hypothesized matter component quantified as a mass or a fraction of the universe's total mass-energy density

Recovery means

Not applicable

Measured by

Inferred gravitationally from galactic rotation curves, velocity dispersions in clusters, gravitational lensing, large-scale structure, and cosmic microwave background fits; sought directly through underground particle-detection and collider experiments