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Protoplanetary Disks

October 4, 2010

To make a star, you first need to make a pancake.

Start with some basic ingredients. First come large dollops of hydrogen and helium gas. They were formed in the Big Bang, and they're the most abundant elements in the universe. Then mix in some small grains of "dust" -- solid particles made of elements like silicon, oxygen, carbon, magnesium, and iron, which were forged in the hearts of stars.

This mixture forms a giant cloud, which can span up to a hundred light-years or more. Eventually, a small part of the cloud -- its dense core -- begins to collapse as its gravity overcomes its internal pressure.

As the core collapses, it spins faster and faster -- like a skater who speeds up as she pulls in her arms. Material that's along the spin axis falls straight toward the middle. But material away from the axis forms a wide but thin disk -- like a pancake.

The disk funnels much of its gas and dust toward the core. When the core gets hot enough, it ignites nuclear fusion -- and a new star is born.

Winds and radiation from the young star then blow away much of the remaining gas and dust around it -- but not all. Some of it clumps together, like lumps of batter in an otherwise smooth pancake. Many of the lumps coagulate to form planets. But just how they do so is a bit of a mystery, which we'll talk about tomorrow.


Script by Damond Benningfield, Copyright 2010

Today's program was made possible in part by the NASA Science Mission Directorate.

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