Abell 2142: A cluster of galaxies in the constellation Corona Borealis.
Caption: This image made by NASA's Chandra X-ray Observatory shows the merger of two sub-clusters of galaxies. The sub-clusters are embedded within Abell 2142, a gigantic galaxy cluster that is one of the most massive objects in the universe. The smoothness of the elongated cloud in the Chandra image suggests that these sub-clusters have collided two or three times in a billion years or more, and have nearly completed their merger. The bright source in the upper left is an active galaxy in the cluster.
Scale: Image is 7.5 x 7.2 arcmin on a side.
Chandra X-ray Observatory ACIS Image