Theorists divide supernovae into two types:
core-collapse supernovae and thermonuclear detonation
supernovae.  The first type occurs when a massive star
exhausts its thermonuclear fuel.  The second type occurs
when a white dwarf experiences a thermonuclear runaway
after becoming gravitationally unstable.  These rare but
intense explosions can be seen across the universe.  They
are responsible for all of the heavy elements in the universe,
and are therefore necessary for human life.