Free Astronomy Magazine January-February 2016

SPACE CHRONICLES To make these discover- ies, the team utilised the deepest images of gravi- tational lensing made so far in three galaxy clus- ters, which were taken as part of the Hubble Fron- tier Fields programme, a three-year, 840-orbit pro- gramme which will yield the deepest views of the Universe to date, combin- ing the power of Hubble with the gravitational am- plification of light around six different galaxy clus- ters to explore more dis- tant regions of space than could otherwise be seen. These clusters generate immense gravitational fields capable of magnifying the light from the faint galaxies that lie far behind the clusters themselves. T his image from the NASA/ESA Hubble Space Telescope shows the galaxy cluster MACS J0717.5+3745. Due to the huge mass of the cluster it is bending the light of background ob- jects, acting as a mag- nifying lens. It is one of the most massive gal- axy clusters known, and it is also the largest known gravitational lens. Of all of the galaxy clusters known and measured, MACS J0717 lenses the largest area of the sky. [NASA, ESA and the HST Frontier Fields team (STScI)] Kneib, co-author of the study from the Ecole Polytechnique Fédérale de Lausanne, Switzerland, explains, “Clusters in the Frontier Fields act as powerful natural tele- scopes and unveil these faint dwarf galaxies that would oth- erwise be invisible.” Co-author of the study Mathilde Jauzac, from Durham Universi- ty, UK, and the University of KwaZulu-Natal, South Africa, remarks on the significance of the discovery and Hubble’s role in it, “Hubble remains unrivalled in its ability to observe the most distant galaxies. The sheer depth of the Hubble Frontier Fields data guarantees a very precise understanding of the cluster magnification effect, al- lowing us to make discoveries like these.” These results highlight the im-pressive possibilities of the Frontier Fields programme with more galaxies, at even earli- er time, likely to be revealed when Hubble peers at three more of these galaxy clusters in the near future. A bell 2744, nicknamed Pandora’s Clus- ter, was the first of six tar- gets within the Frontier Fields programme, which together have produced the deepest images of gravitational lensing ever made. The clus- ter is thought to have a very violent history, having formed from a cosmic pile-up of mul- tiple galaxy clusters. [NASA, ESA and the HST Frontier Fields team (STScI)] This makes it possible to search for, and study, the first generation of galaxies in the Universe. Jean-Paul n