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Ask an Astrophysicist

The Question

(Submitted February 28, 2003)

Recently I learned that white dwarf stars have a core that can become a diamond over millions of years because of the pressure exerted on it by gravity. Is this true? Are there white dwarfs in the universe that are literally orbiting in galaxies as dead stars with a diamond core?

The Answer

Yes, it's true that white dwarf stars will eventually form a core of crystallized carbon, much like terrestrial diamonds, with a little bit of oxygen impurity. When a star like our sun extinguishes its fuel, it will leave behind a hot core at a temperature of 100,000 degrees with a surface gravity 100,000 times that of Earth. In this resulting white dwarf the heaviest elements (carbon and oxygen) sink to the center, while hydrogen and helium rise to form an atmosphere around the cooling star. By measuring pulsations of a nearby cooling white dwarf, astronomers were able to determine that the interior of the star had partly solidified. It takes a few billion years to cool, but white dwarfs do essentially form giant diamonds in their interiors.

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