Astrophys. J. 697, 1493–1511 (2009)

Many astronomers have thought that most of the large, mature galaxies in the Universe took a long time to get that way, as smaller galaxies burst onto the scene and merged into larger ones over billions of years. But Daniel Stark of the University of Cambridge, UK, and his colleagues have found that the early Universe may have been a more active galactic crucible.

Using Hubble Space Telescope data, the researchers identified more than 3,000 galaxies that formed up to about 12 billion years ago, when the Universe was only 1.7 billion years old. Many of these galaxies were already big, suggesting that these earliest epochs of the Universe were very busy times, and probably responsible for the formation of a significant component of the Universe's mature, massive galaxies.