After the protons and electrons combined to produce the first hydrogen atoms, the universe contained a nearly uniform, almost completely neutral, intergalactic medium (IGM) for which the most amount of matter component was hydrogen gas. With no glowing sources present, these are known as the Dark Ages. Theoretical models predict that, over the next few hundred million years, gravity slowly condensed the gas into denser and denser regions, in which the first stars eventually appeared, marking Cosmic Dawn.