Modern galaxies like our own Milky Way became giants by swallowing their smaller neighbors and absorbing their billions of stars. But how did the earliest galaxies grow when there weren't nearly as many stars to swallow? A new study, reported  online today in Nature, suggests that they swallowed the ingredients for stars instead. A team studying three galaxies that formed over 11 billion years ago observed them all sucking up cold, primordial hydrogen and helium gas from intergalactic space and churning out new stars in their central, star-making regions. Once the gas disappears, the galaxies either acquire new stars via mergers or in the aftermath of supernova explosions, which seed the heavens with heavier elements.
See more ScienceShots .