Warm–hot intergalactic medium

The warm–hot intergalactic medium (WHIM) is the sparse, warm-to-hot (105 to 107 K) plasma that cosmologists believe to exist in the spaces between galaxies and to contain 40–50%[1][2] of the baryonic 'normal matter' in the universe at the current epoch.

[3] The WHIM can be described as a web of hot, diffuse gas stretching between galaxies, and consists of plasma, as well as atoms and molecules, in contrast to dark matter.

To locate the WHIM, researchers examined X-ray observations of a rapidly growing supermassive black hole known as an active galactic nucleus, or AGN.

[7] In May 2010, a giant reservoir of WHIM was detected by the Chandra X-ray Observatory lying along the wall-shaped structure of galaxies (Sculptor Wall) some 400 million light-years from Earth.

[9] Conceptually similar to WHIM, circumgalactic medium (CGM) is a halo of gas between the ISM and virial radii surrounding galaxies that is diffuse, and nearly invisible.