Universe’s Missing Baryons Found in Intergalactic Medium

Ordinary (baryonic) matter make up all physical objects in existence, from stars to the cores of black holes. But until now, scientists had only been able to locate about two-thirds of the matter that theorists predict was created by the Big Bang. In new research, a multinational group of astronomers and astrophysicists pinned down the missing third, finding it in hot and tenuous filamentary gas between galaxies, known as the warm-hot intergalactic medium (WHIM).

“The lost matter exists as filaments of oxygen gas at temperatures of around one million degrees Celsius,” said co-author Professor Michael Shull, a researcher in the Department of Astrophysical Science at the University of Colorado, Boulder. “This is one of the key pillars of testing the Big Bang theory: figuring out the baryon census of hydrogen and helium and everything else in the periodic table.”

Astrophysicists have a good idea of where to find most of the ordinary matter in the Universe, which is not the same as dark matter: about 10% sits in galaxies, and close to 60% is in the diffuse clouds of gas that lie between galaxies.