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STARS: Life Span of Stars |
 Home  Stars  Planets  Satellites  Galaxies and Nebulae 
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Stars are born in a great cloud of hydrogen gas and dust called a nebula. This begins to break up and shrink into spinning balls. Then each ball becomes so incredibly hot in its centre that nuclear reactions are triggered, and the hydrogen starts to turn into another gas called helium. The young star now glows brightly and gives off vast amounts of heat. The biggest stars are called giants, and they can have 20 or 30 times as much gas in them as our Sun. They blaze brightly, but soon burn up their gas fuel. Small, dim stars are called dwarfs. The brightness of the stars we see from Earth depends on their size and how far away they are from us. A red giant is an old star which has swollen to many times its normal size. This final blaze of glory happens when the star's helium core collapses and gets hot enough to blow its hydrogen up into a vast orange-red ball. The biggest stars may swell into supergiants, 2,000 times the size of our Sun. A white dwarf is almost the final stage in a star's life. The gas surface of the red giant is blown off, and the star is now a planetary nebula. In the centre of the gas shell is the giant's hot, shrunken core- awhite dwarf star. Over billions of years, this fades into a cinder and dies. Really massive stars- at least eight times the size of the sun- don't fade slowly. They go out with an almighty bang and look like a bright, new star. Exploding stars are called supernovas.
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