Hubble - greatest discoveries
How astronomers use a helping hand from Einstein to increase Hubble's range
Light does not always travel in straight lines. Einstein predicted in his Theory of General Relativity that massive objects will deform the fabric of space itself. When light passes one of these objects, such as a cluster of galaxies, its path is changed slightly. This effect, called gravitational lensing, is only visible in rare cases and only the best telescopes can observe the related phenomena. Hubble's sensitivity and high resolution allow it to see faint and distant gravitational lenses that cannot be detected with ground-based telescopes. The gravitational lensing results in multiple images of the original galaxy each with a characteristically distorted banana-like shape or even into rings.
Hubble was the first telescope to resolve details within these multiple banana-shaped arcs. Its sharp vision can reveal the shape and internal structure of the lensed background galaxies directly and in this way one can easily match the different arcs coming from the same background object – be it a galaxy or even a supernova – by eye. Since the amount of lensing depends on the total mass of the cluster, gravitational lensing can be used to "weigh" clusters. This has considerably improved our understanding of the distribution of the dark matter in galaxy clusters and hence in the Universe as a whole. The effect of gravitational lensing also allowed a first step towards revealing the mystery of the dark energy.
This is one of nine articles highlighting some of the greatest discoveries made by the Hubble Space Telescope. Read more in the articles linked from the right-hand menu.