Many of the brightest blue images are of a single, unusual, beaded, blue, ring-like galaxy which just happens to line-up behind a giant cluster of galaxies. Cluster galaxies here typically appear yellow and — together with the cluster’s dark matter — act as a gravitational lens.
A gravitational lens can create several images of background galaxies, analogous to the many points of light one would see while looking through a wine glass at a distant street light. The distinctive shape of this background galaxy — which is probably just forming — has allowed astronomers to deduce that it has separate images at 4, 10, 11, and 12 o’clock, from the center of the cluster.
This spectacular photo of galaxy cluster CL0024+1654 from the Hubble Space Telescope was taken in November 2004.
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