A 400-year-old supernova explosion creates a spectacular scene.
This supernova remnant is the result of a Type Ia supernova explosion. The explosion was observed by Danish astronomer Tycho Brahe in 1572. The ejected matter from the explosion has expanded to fill a sphere 55 light-years across. In the image, low-energy X-rays are shown in red, illustrating the expanding debris from the supernova explosion, and blue high-energy X-rays show the blast wave — a shell of extremely energetic electrons. Type Ia supernovas, which originate from white dwarfs, play an important role in measuring the universe, as they are bright enough to be seen across large distances and bright enough to act as a standard candle — the basic unit of luminous intensity. They were also used to discover the existence of dark energy.