Astronomers Have Been Watching a Supernova's Debris Cloud Expand for Decades with Hubble

Twenty thousand years ago, a star in the constellation Cygnus went supernova. Like all supernovae, the explosion released a staggering amount of energy. The explosion sent a powerful shockwave into the surrounding space at half a million miles per hour, and it shows no signs of slowing down. For twenty years, the Hubble Space Telescope …