StarChild Question of the Month for May 2003


Is my body really made up of star stuff?

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Virtually all of the elements we see on the Periodic Table were made at some point during the life and death of a star. Only hydrogen, helium, and lithium were created in a different way, i.e., they were created as a result of the Big Bang explosion.

So how dos a star make the elements heavier than lithium? A star's energy comes from combining light elements into heavier elements in a process known as fusion, or "nuclear burning". It is generally believed that most of the elements in the universe heavier than helium were created in stars when lighter nuclei fuse to make heavier nuclei. The process is called nucleosynthesis.

Nucleosynthesis requires a high-speed collision, which can only be achieved with very high temperature. The minimum temperature required for the fusion of hydrogen is 5 million degrees. Elements with more protons in their nuclei require still higher temperatures. For instance, fusing carbon requires a temperature of about one billion degrees! Most of the heavy elements, from oxygen up through iron, are thought to be produced in stars that contain at least ten times as much matter as our Sun.

Our Sun is currently burning, or fusing, hydrogen to helium. This is the process that occurs during most of any star's lifetime. After the hydrogen in the star's core is exhausted, the star can fuse helium to form progressively heavier elements, carbon and oxygen and so on, until iron and nickel are formed. Up to this point, the fusion process releases energy. The formation of elements heavier than iron and nickel requires an input of energy. Supernova explosions result when the cores of massive stars have exhausted their fuel supplies and burned everything into iron and nickel. The nuclei with masses heavier than nickel are observed to be formed during these explosions.

So indeed - we are all made out of star stuff!

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