Where did planets, stars, and galaxies come from?
Most theoretical models for galaxy formation have assumed that galaxies form through mergers of smaller building blocks. These building blocks are essentially mini-galaxies full of hydrogen gas and young stars. Hubble pictures of the most distant galaxies are corroborating these models in two important ways. First, Hubble is showing that there were many more unusually shaped galaxies early on in the universe than there are now, indicating that collisions and mergers were indeed more common during the first few billion years. Second, Hubble is finding numerous mini-galaxies in the early universe that are bursting with new star formation.
