What is a supernova?

A supernova is a violent, cataclysmic explosion of a “red giant” star that has aged billions of years to the point where it has burned all of its fuel in the form of noble gases and heavier elements. At this point, the star no longer has the outward nuclear fusion reactions to withstand its own gravity. The star instantaneously implodes, causing a “gravity rebound” explosion of inconceivable magnitude. The star dies, leaving behind a cosmic cloud of its remnants or, in rare cases, a black hole.