Portal:Astronomy/Picture/24 May 2005
< Portal:Astronomy | Picture
The galaxy cluster Abell 1689 acts as a giant lens, distorting the light from a more distant cluster behind it into numerous faint blue arcs in a process known as gravitational lensing. The effect can be used to measure the mass of the cluster, and reveals the presence of large amounts of dark matter. Credit: NASA, the ACS team and ESA