The explosive death of a star, which
temporarily attains a brightness of 100
million Suns or more, so that it can shine as
brilliantly as a small galaxy for a few days
or weeks. Type I supernovae are thought to
occur in binary star systems in which gas
from one star falls on to a white dwarf,
causing it to explode. Type II supernovae
occur in stars ten times or more than the
Sun, which suffer runaway internal nuclear
reactions at the ends of their lives, leading
to explosions. These are thought to leave
behind neutron stars and black holes. Gas
ejected by such an explosion causes an
expanding radio source, such as the Crab
nebula. Supernovae are thought to be the main
source of elements heavier than hydrogen and
helium. The last supernova occurring in our
Galaxy was in 1604, but they occurred since
in other galaxies. In 1987 a supernova
visible to the unaided eye occurred in the
Large Magellanic Cloud, a small neighbouring
galaxy. Eta Carinae, visible in the
constellation Carina in the southern
hemisphere, may become a supernova in a few
hundred years.