MARK GARLICK / SCIENCE PHOTO LIBRARY MARK GARLICK / SCIENCE PHOTO LIBRARY
Supergiant star's core, artwork. When a supergiant star (10-70 solar masses) uses up the hydrogen at its core, the nuclear fusion processes start to produce successively heavier elements that form shells of 'ash' that accumulate at the centre of the star. These shells are shown at left, labelled by their chemical symbols (H - hydrogen; He - helium; C - carbon; Ne - neon; O - oxygen; Si - silicon; and Fe - iron). The nuclear fusion reactions to produce iron, unlike the other reactions, do not produce enough energy to prevent the core collapsing. A rebounding shock wave (not shown) blows off the star's outer layers at thousands of kilometres a second, distributing the heavy elements to form planets and life. A supernova may briefly outshine an entire galaxy.
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