Hubble image of galaxy cluster MACS J1206
This image from the NASA/ESA Hubble Space Telescope shows the galaxy cluster MACS J1206. Galaxy clusters like these have enormous mass, and their gravity is powerful enough to visibly bend the path of light, somewhat like a magnifying glass.
These clusters are useful tools for studying very distant objects, because this lens-like behaviour amplifies the light from faraway galaxies in the background. They also contribute to a range of topics in cosmology, as the precise nature of the lensed images encapsulates information about the properties of spacetime, the expansion of the cosmos and the distribution of dark matter within the cluster.
This is one of 25 clusters being studied as part of the CLASH (Cluster Lensing and Supernova survey with Hubble) programme, a major project to build a library of scientific data on lensing clusters.