ESA's XMM-Newton finds huge filament of missing matter

Astronomers have found a filament of hot gas, ten times as massive as our galaxy, that they reckon could explain where at least some of the universe's "missing" matter might be lurking.

A third of "normal" matter in the universe is "missing." It's needed to make scientists' models of the cosmos operate as postulated, but has proven difficult to find. The material is the ordinary stuff known as baryonic matter (baryons include protons and neutrons and other subatomic particles that make up the visible universe – not to be confused with dark matter or dark energy.) Physicists put the mass ratio of dark matter to baryonic matter at 5 to 1, meaning only approximately 15 or 16 percent of matter in the universe is normal matter. And according to a recent Nature Astronomy paper, only a "small fraction of baryons are in stars and the interstellar medium within galaxies ...