You're looking at ACT-CL J0102-4915. To it's stargazing buddies, though, it's better known as El Gordo—literally, "the fat one"—because it's the largest known galaxy cluster in the distant universe.

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Researchers have worked that out by measuring how much the cluster's gravity warps images of galaxies in the distant background. The latest results show that it weighs 3 million billion times as much as our sun—43 percent more massive than earlier estimates. This image, which was used in the analysis, was captured by Hubble. [NASA]

Image by NASA/ESA