Supernova 1997ff
The detection and analysis of the most distant supernovae shows they are further away than expected, leading to the notion of some form of "dark energy" accelerating the expansion of the universe. These images from NASA's Hubble Space Telescope show supernova 1997ff in its cosmic neighbourhood (top), home galaxy (left), and the dying star itself (right). (NASA and A Riess, STScI.)