When light from far-off galaxies passes near a massive object on its way toward us, the warped spacetime in the area bends the light’s path. That effect, known as gravitational lensing, produces distorted, magnified, and sometimes multiple images of the distant galaxies and is a powerful tool for studying cosmic expansion and the structure of the universe (see the article by Leon Koopmans and Roger Blandford, Physics Today, June 2004, page 45). The Hubble Space Telescope Frontier Fields program, begun last fall, is exploiting the gravitational lensing by six galaxy clusters to probe the very distant, ancient universe.
This Hubbleimage shows one of the clusters, MCS J0416.1–2403, some 5.5 billion light-years away. During 80 orbits earlier this year, the telescope trained its Advanced Camera for Surveys on the cluster. An international team of astronomers has now used the collected data to map the cluster’s mass with unprecedented...
