Brief Introduction

Fifteen billion years after the big bang, matter is no longer spread evenly through space, as it did in the early universe. Instead it appears in clumps called stars, which themselves clump into galaxies and galaxy clusters. Such clumps have apparently bound themselves together through their self-gravitational forces early in the history of the universe. They then contracted toward their present sizes as the rest of the universe continued its expansion. The details of how this "clumping" occurred from a rather uniform universe are not yet known.

This is an exceptional picture from the Hubble space telescope peering towards the edges of the Universe. Some of the faintest objects ever imaged are shown here (four billion times fainter than what it could be seen with the naked eye). The field of view shown here is 1/30th of the diameter of the moon as seen from Earth.

Recognizable in this picture are several types of galaxies discussed below, such as spiral galaxies (center-left of the picture), elliptical galaxies, and irregular galaxies (upper right corner) . Although the image above has not been analyzed yet to establish the distances of these galaxies from us, it is reasonable to think that these are among the oldest large scale objects in the universe. The reddish "fuzz balls" in the picture are likely to be galaxies in the early stages of formation. Thus this picture and similar pictures, when fully analyzed (and this might take up to a year), can give us important clues on how galaxies are formed, something that is not yet fully understood.