The pattern of arcs over this HST image of the galaxy cluster Abell 2218 is a spectacular example of the gravitational lensing phenomenon. The arcs are the distorted images of very remote galaxies five to ten times farther away than Abell 2218. These galaxies existed when the universe was only one quarter its present age.
Abell 2218 is such a massive, compact cluster that light rays passing though it are markedly deflected by its enormous gravitational field. The process magnifies, brightens and distorts images of the galaxies far beyond it. In this way, Abell 2218 acts as a powerful 'zoom lens' making it possible to view galaxies so far away that they would not otherwise be visible, even with the most powerful telescopes available. The arcs provide a direct glimpse of how star forming regions are distributed in remote galaxies, and other clues to the early evolution of galaxies. The resolution of the HST reveals numerous arcs that are difficult to detect with ground-based telescopes because they appear so thin. In seven cases, multiple images of the same galaxy can be seen in the HST view.
Camera: WFPC2
Credit: W. Couch (University of New South
Wales), R. Ellis (University of Cambridge), and NASA
