February 17, 2005Squares mark the six barely visible, red-
toned members of a galaxy cluster captured by Japan's Subaru
Telescope. Their relative closeness (a mere 300 light-years separates
the farthest members) qualifies them as a galaxy cluster, the largest
type of astronomical object in the universe. This group's presence at
a far edge of the universe marks it as the oldest known cluster.
Astronomers say it formed when the universe was only a billion years
old, assuming the universe is about 13 or 14 billion years old.
How can we measure the cluster's age? Because astronomers are able to analyze light waves and thereby tell how long it took for the light, and the images the light creates, to reach Earth. The light that created the images of the galaxies in the photo above is about 12.7 billion years old, so you're actually looking into the distant past as well as the distant limits of the universe.