Gravity amplifies slight irregularities in the density of the primordial gas.
Even as the universe continues to expand rapidly, pockets of gas become more and more dense. Stars ignite within these pockets, and groups of stars become the earliest galaxies. This point is still perhaps 12 to 15 billion years before the present. The Hubble Space Telescope recently captured some of the earliest galaxies ever viewed. They appear as tiny blue dots in the Hubble Deep Field, the image on the left.