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Cold dark matter


In cosmology and physics, cold dark matter (CDM) is a hypothetical form of dark matter whose particles moved slowly compared to the speed of light (the cold in CDM) since the universe was approximately one year old (a time when the cosmic particle horizon contained the mass of one typical galaxy); and interact very weakly with ordinary matter and electromagnetic radiation (the dark in CDM). It is believed that approximately 84.54% of matter in the Universe is dark matter, with only a small fraction being the ordinary baryonic matter that composes stars, planets and living organisms.

The theory was originally published in 1982 by three independent groups of cosmologists; James Peebles, J. Richard Bond, Alex Szalay and Michael Turner; and George Blumenthal, H. Pagels and Joel Primack. An influential review article in 1984 by Blumenthal, Sandra Moore Faber, Primack and Martin Rees developed the details of the theory.

In the cold dark matter theory, structure grows hierarchically, with small objects collapsing under their self-gravity first and merging in a continuous hierarchy to form larger and more massive objects. In the hot dark matter paradigm, popular in the early 1980s, structure does not form hierarchically (bottom-up), but rather forms by fragmentation (top-down), with the largest superclusters forming first in flat pancake-like sheets and subsequently fragmenting into smaller pieces like our galaxy the Milky Way. Predictions of the cold dark matter paradigm are in general agreement with astronomical observations.


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