What Is the Primary Composition of a White Dwarf?

White dwarfs form from stars the size of our sun that have burned most of their fuel.

A white dwarf is a star that has exhausted most of its fuel. White dwarfs are one of the densest forms of matter, being 200,000 times as dense as the earth. They are formed from small to medium-sized stars.

Atmosphere

Because of its density, the surface gravity of a white dwarf is very great. The force of this gravity causes the heavier atoms in its atmosphere to sink, while the lighter atoms remain at the surface. As a result, white dwarfs have atmospheres that are composed of hydrogen or helium, two of the lightest elements. This atmosphere forms a very thin layer above the surface of the star.

Core

The surface of the white dwarf itself is thought to be made up of a crust that is 50 kilometers thick. Underneath this crust is a crystalline lattice of carbon and oxygen atoms.

Unusual White Dwarfs

A very few white dwarfs, formed from larger stars, have atmospheres that are rich in oxygen. These white dwarfs have burned the carbon they once contained and the oxygen in their atmosphere is what remains of their cores.

References

• NASA Goddard Space Flight Center: White Dwarf Stars
• Universe Today: Unusual Massive White Dwarf Stars Have Oxygen Atmospheres