Distant Galaxy Clusters

This NASA Hubble Space Telescope image reveals one of the faintest and probably farthest clusters of galaxies ever seen. The cluster contains about 30 very faint objects which are unusually small and compact in appearance. (The larger objects are foreground galaxies located in a separate galaxy cluster four billion light-years away). These lumpy spots do not appear to resemble the elliptical and spiral galaxies of today. The objects might not be separate galaxies but rather sites of strong star formation embedded within primordial galaxies which are too faint to be seen in this HST exposure. The colors of these objects (measured with the Mount Palomar 200-inch telescope), place the cluster at a distance of at least seven billion light-years (redshift z > 1.) The cluster may be even farther if it is associated with a quasar (located near the left edge of the frame) which has a measured distance of ten billion light-years ( redshift z = 2.055). Though the superposition of the cluster objects and the quasar could be a coincidence, both are so unusual they probably all are members of the same cluster, at the same distance. If so, then this corresponds to the early epoch of galaxy formation, about ten billion years ago. The image was taken with HST's Wide Field/Planetary Camera in Wide Field Camera mode, and required a 6-hour exposure.