Hubble image of galaxy cluster Abell 1689, showing a large number of lensed arcs. These arcs are distorted images of background galaxies, gravitationally lensed by the mass of the cluster.
Credit: NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of
Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI), G.
Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science
Team and ESA