It is estimated that there are at least 10¹¹ galaxies in the universe today. The current rate of expansion of the universe is increasing, which pushes galaxies away from each other. However, on an intermediate scale (millions of light years), galaxies tend to form clusters. For example, our Milky Way galaxy is part of the local group known as the Virgo Super-Cluster, and will collide with the Andromeda Galaxy (M31) in about 3 billion years.

Galaxy Cluster SXDF/FCC-A (Courtesy: NAOJ)There is considerable uncertainty about the first appearance of the galaxies after the big bang. This birthday (of sorts) is continuously being pushed back. Recently, researchers from the University of Tokyo, the National Astronomical Observatory of Japan (NAOJ), and those using the Subaru Telescope have found that clusters of galaxies were already forming about 1 billion years after big bang. This pushes back the age of the earliest known clusters by a third, and shows that the largest structures in the universe had already started to form during the earliest epoch the astronomers have yet been able to observe.
The above image shows the characteristically red color of the (six) galaxies in the cluster. This corresponds to a red-shift of 5.7, and a distance of 12.7 billion years. The area in the image is approximately 1° square area of the sky, in the direction of the constellation Cetus.
The galaxies are concentrated in a volume only 6 million light years in diameter (the Virgo SuperCluster, in comparison, is over 200 million light years in diameter). The cluster is about 100 times less massive, and the member galaxies are producing stars at 100 times the rate of modern galaxies.
These results were published in the February 10, 2005, edition of the Astrophysical Journal (ApJ 620, L1-L4) and will be presented at the meeting The Future of cosmology with clusters of Galaxies beginning on February 26, 2005, in Waikoloa, Hawaii.