Taken by Hubble's Advanced Camera for Surveys Wide Field Camera in July 2002, this image shows the embryonic cluster as it was when the universe was just 1.5 billion years old. This is the most distant proto-cluster known. It is dominated by a massive baby galaxy, seen as the green object near the center of this image. The galaxy is producing powerful radio emissions, and it is the brightest galaxy in the proto-cluster. The green color is indicative of glowing hydrogen gas. The galaxy's clumpy appearance suggests it is still developing. Smaller growing galaxies are scattered around the massive galaxy. The bright object in the upper part of the image is a foreground star.
NASA / ESA / G. Miley and R. Overzier (Leiden Observatory)