Two Space Telescopes

The galaxies being lensed in the figure below are normally too faint even for the Hubble Space Telescope to see. In a case of strong lensing as exhibited here, the foreground cluster acts as a "zoom lens", magnifying and brightening distant galaxies that would otherwise not be visible. In effect there are two space telescopes, one natural, and one man-made, involved in obtaining this image (more precisely, there is one space telescope and one natural space lens)!

A Gallery of Lenses

The following Hubble Space Telescope image shows a spectacular example of a gravitational lens. The pattern of many small arcs spread across the picture is an illusion caused by the gravitational field of the rich galaxy cluster, Abell 2218, which lies in the foreground (the galaxies of the rich cluster are the bright patches of light that look like elliptical and spiral galaxies; the lensed galaxies are the whispy, elongated arcs).
Lensing by a Large Cluster
The cluster is so massive and compact that light rays passing through it are deflected by its enormous gravitational field and the arcs are actually distorted images of very distant galaxies. The foreground cluster Abell 2218 lies at a relatively low redshift of z = 0.18, which corresponds to a distance of around 800 Mpc. The galaxies being lensed in the arcs are much further away, probably lying at redshifts of 2 or greater. They are so distant that we are seeing them when the Universe was only about 1/5 its present age.

As noted in the right frame, this example also exhibits multiple imaging, with more than one copy of some galaxies appearing in the image.