The objects typically measure only 2,000 light-years across. That's not very big. The objects are much smaller than even the central bulge of the Milky Way, which measures about 8,000 light-years in diameter. In fact, at least four of the objects in this field show double structure in their centers only a few thousand light-years apart, as if we've caught them in the act of falling together. We are convinced that these objects are not peculiar, but part of the general formation process of galaxies in the early universe.
Astronomers see stars form, because star formation is an ongoing process.
However, astronomers have never directly seen galaxies form, because their formation may have happened a long time ago, or because galaxy formation is not as spectacular as once believed, and is therefore much harder to observe. The idea that galaxies grew from small pieces coming together, rather than through the collapse of a gigantic gas cloud, has been predicted from previous theoretical work and ground-based observations. The Hubble observations offer some of the best direct visual evidence to date, says Pascarelle. Though many of the objects are isolated in the image, they are close enough together in space that most of them should eventually merge, according to Windhorst. He sketches a scenario where two or more objects will pass through each other, drawing out hydrogen gas to form more stars later.