User:Olaf Davis/Warm-hot intergalactic medium

The warm-hot intergalactic medium (WHIM) refers to a sparse, hot gas which is believed by cosmologists to exist in the spaces between galaxies and to contain a significant fraction of the baryons (that is, 'normal matter' which exists as atoms and molecules, in contrast to dark matter) in the universe at the current epoch.

The total amount of atomic matter (baryons) in the universe can be estimated from models of Big Bang nucleosynthesis, which relates baryon content to the observed abundance of different elements. This indicates that around 4-5% of the mass-energy in the universe is composed of baryons (the rest being almost all dark matter and dark energy). When we observe regions of the universe at redshift above 2 (i.e., objects whose light now reaching us was emitted more than 10 billion years ago) most of this mass is accounted for in the Lyman-alpha forest.