Once-in-a-lifetime event : Astronomers successfully predict a distant supernova replay in advance

Gravitational lensing, the deflection of light by gravity, has tremendously contributed over the past twenty years to our understanding of the mass distribution in galaxies and galaxy clusters and of the distant Universe. Gravitational lensing has demonstrated its great potential for future studies about the mysterious dark-matter and dark-energy mass components in the Universe. By exploiting the synergy between superb Hubble Space Telescope and Very Large Telescope data, an international group of astronomers have constructively worked together to obtain high-quality mass reconstructions of a massive cluster of galaxies and have provided the first-ever successful predictions of position, magnification and time delay of a distant lensed supernova, before it actually became visible!