Bright X-Ray Cluster Acts As Strong Gravitational Lens

This is an optical image of the most luminous ROSAT cluster of galaxies RXJ1347.5-1145, obtained with the MPG/ESO 2.2-metre telescope at the La Silla Observatory. The image shows the central part of the cluster with two bright gravitational arcs.

The arcs are 5 - 6 arcseconds long and located about 35 arcseconds to the North-East and South-West of the brightest galaxies in the cluster. They were detected on exposures of only 3 minutes duration with the 2.2-metre telescope and are among the brightest such arcs ever found.

At the distance of the cluster, approx. 5,000 million light-years, the arcs are situated at a projected distance of about 500,000 light-years from the centre of the cluster. It is an interesting possibility that the two arcs may in fact be two images of the same, very distant galaxy, that is situated far beyond RXJ1347.5-1145 and whose light has been bent and split by this cluster's strong gravitational field.