Galaxies through a Lens

This image is taken by the Hubble Space Telescope showing visible light from stars.  This is a very famous cluster called Abel 2218.  Einstein predicted an effect called "gravitational lensing" in the early 20th century, where the light from background galaxies is bent and magnified by a massive object in front of it, similar to light being magnified by a normal glass lens. In this image you can see all the arcs of light caused by this massive cluster of galaxies in the centre of this image.    Herschel-ATLAS will be looking for a different kind of lens system, not one with a cluster of galaxies in front, but one where a massive elliptical galaxy acts as the  gravitational lens.   Observations of the lenses allows us to view these distant galaxies as they were billions of years ago. Without the effect of gravitational lensing, these galaxies would be much fainter, but the scenario provides the opportunity to explore faint galaxies which we would not easily see without the lens in the way. We expect to detect approximately 300 gravitationally lensed systems.

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