Using the FORS2 multi-mode instrument as a spectrograph, they measured the distances to a number of very remote galaxies, located far out in space behind two clusters of galaxies. Such observations may help to determine the values of cosmological parameters that define the geometry and fate of the Universe. After two nights of observations, the astronomers came away from Paranal with a rich harvest of data and a good feeling. We are delighted that the telescope performed so well. It opens a new window towards the distant, early Universe.
Clusters of galaxies are very massive objects.
The clusters thus function as gravitational lenses . In a few cases, the images of the objects behind the clusters are split into several components. Knowing the distance to the objects for which we see multiple images and the distribution of matter in the cluster that produce the lensing effect allows to determine the geometry of the universe in the corresponding direction , independently of its rate of expansion. Detailed observations of these cosmic mirages thus have a direct implication for our understanding of the universe in which we live. This cluster was first discovered by American astronomer George Abell some thirty years ago when he studied photographic plates obtained at the Palomar Observatory.