Nucleosynthesis

StarDate: August 10, 2009

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The alchemists of old tried to transmute lead or other metals to gold. Try as they might, though, they failed. That's because there's only one place to make gold: in the heart of a star.

In fact, that's where almost all of the chemical elements are created, through a process known as nucleosynthesis.

When a star is born, it consists mainly of the lightest element of all, hydrogen, which was created in the Big Bang. Gravity squeezes the star, making its interior very hot. At temperatures of millions of degrees, the hydrogen atoms "fuse" together to make helium. That's what's happening right now in the Sun; more about that tomorrow.

When the hydrogen is used up, many stars fuse the helium to make carbon. And if a star is heavy enough, it can continue the process all the way up to iron.

The elements heavier than iron can be made in a couple of ways.

In many stars, they're made by slowly adding neutrons to the atoms. This builds up elements like gold.

The heaviest stars follow this process, but they also follow the second. At the ends of their lives, their cores are converted to iron. It takes too much energy to fuse the iron atoms together, so the star's core collapses and its outer layers are blasted into space. The explosion is so powerful that atoms slam together in a torrent of nucleosynthesis, creating a stew of almost every chemical element.

The explosion sprays these elements into the universe, where they can help form new stars, planets -- and people.

Script by Damond Benningfield, Copyright 2009

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