Supernova II result from the explosive death of a massive star (Red Giant). They occur in stars at least ten times more massive than our Sun, which suffer runaway thermo-nuclear reactions at the end of their lives, leading to explosions. Such explosions can be either total (no solid remnant) or may leave behind a rapidly spinning neutron star (a pulsar) or a black hole. The Supernova II remnant (the dust cloud that expands from the explosion) remains for many years. The flash only lasts a few seconds.