Pre-Supernova Star
Figure 6 : An artists depiction of the interior of a heavyweight star just before it explodes as a supernova. The whole star may be as big as the orbit of Mars, but the nuclear furnace is not much bigger than the Earth and comprises a set of nested shells each burning a different nuclear fuel, from ligher elements on the outside to heavier elements towards the center. The innermost region is a ball of highly compressed iron which ultimately collapses to trigger the explosion.