NASA's Hubble Space has peered nearly 5 billion light-years away to resolve intricate details in the galaxy cluster Abell 370. This object is one of the very first galaxy clusters where astronomers observed the phenomenon of gravitational lensing, where the warping of space by the cluster's gravitational field distorts the light from galaxies lying far behind it. This is manifested as arcs and streaks in the picture, which are the stretched images of background galaxies.

Gravitational lensing proves a vital tool for astronomers when measuring the dark matter distribution in massive clusters, since the mass distribution can be reconstructed from its gravitational effects. Galaxy clusters are the most massive structures of the universe, located at the crossing of the filaments of the cosmic web of dark matter. The most massive clusters can contain up to 1,000 galaxies and intergalactic hot gas, all held together primarily by the gravity of dark matter.

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