In two different scientific teams, the award-winning physicists used one type of supernova, supernova Ia , an explosion from an old compact star as heavy as the Sun but smaller than Earth. A single Ia supernova is so powerful it can emit as much light as an entire galaxy. However, the Nobel-winning physicists found several dozen supernovae whose light was weaker than expected, a sign that the expansion of the Universe, which began 14 billion years ago with the Big Bang, is accelerating more and more. This acceleration is thought to be due to dark energy, an element that could constitute three-quarters of the Universe and whose composition is, however, a complete enigma for scientists.