Hubble Spots Distant Supernovae in Search of Properties of Dark Energy

These are images of three of the most distant supernovae known, discovered using the Hubble Space Telescope as a supernova search engine. The stars exploded back when the universe was approximately half its current age. The light is just arriving at Earth now. Supernovae are so bright they can be seen far away and far back in time. This allows astronomers to trace the expansion rate of the universe, and to determine how it is affected by the repulsive push of dark energy, an unknown form of energy that pervaded space.