Cosmology: Mystery of the Missing Mass

In their mind-stretching efforts to explain the universe, cosmologists have been troubled by a glaring inconsistency: the universe behaves as if it is much more massive than it appears.

The total mass of the galaxies, which contain all the stars and thus most of the known matter in the universe, is far too small to account for the declining rate at which the universe is expanding. The missing mass may now have been discovered. A Naval Research Laboratory scientist has found evidence that it exists in the form of a hot gas that fills the void between galaxies.

Astrophysicist Richard Henry...