Carbon

StarDate: August 12, 2009

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Life on Earth is based on a key ingredient: carbon. It easily combines with other elements to make everything from muscle tissue to the DNA that contains our genetic blueprints.

Every carbon atom in every living organism on Earth was manufactured in the heart of a star.

One star that's probably making carbon right now is Arcturus, the brightest star of Bootes. It's high in the west at nightfall, and sets by around 1 or 2 in the morning. It's hard to miss because it's one of the brightest stars in the night sky, shining with a pale orange color.

For most of its life, Arcturus did just what the Sun is doing now: It "burned" the hydrogen in its core to make helium -- a process known as nuclear fusion.

But Arcturus has used up the hydrogen. Its core is shrinking and getting hotter, allowing it to start burning the helium to make carbon. Under the extreme temperatures in the star's core, the helium atoms ram into each other and "fuse" together to make carbon.

When the helium is used up, the nuclear fusion will stop. The core will shrink to about the size of Earth, and the star's outer layers will blow off into space. That expanding bubble will carry away some of the star's carbon -- seeding the galaxy with the raw materials for future planets -- and perhaps even life.

Arcturus isn't the only star that will end its life this way, though. Another is the Sun, which will start making carbon in its core in several billion years.

Script by Damond Benningfield, Copyright 2009

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