White Dwarf: Definition & Size

Instructor: Katie Chamberlain

Katie has a PhD in Microbiology and has experience preparing online education content in Biology and Earth Science.

White dwarfs are not related to Snow White's roommates, although both enjoy a relatively small stature. This lesson will provide you with the details of what it takes to be a white dwarf star.

Definition

A white dwarf is a star at the very end of its life. It occurs when nuclear core fusion ceases in a small- to average-sized main sequence star. A white dwarf is very tiny (for a star), very dense, and very hot as it begins the long cooling process.

White dwarf stars photographed by the Hubble telescope
White Dwarf Stars

Precursor to a White Dwarf

Nearly all stars (97%) will eventually become white dwarf stars, but before a star becomes a white dwarf, it must pass through various other stages of life. All stars are born from nebulas when nuclear fusion of hydrogen begins deep in their cores. They next enter a stable period of their lives known as the main sequence. During this time they will continue to fuse hydrogen into helium in their cores. There will be a balance of gravitational forces pushing inward and core fusion forces pushing outward. Depending on the size of the star, this phase will last between a few million to tens of billions of years.

White Dwarf

When core hydrogen depletes and core fusion ceases, gravitational forces overrun the fusion forces, and the star begins to compact. Small stars then move directly towards the white dwarf phase, whereas medium-sized stars first experience a period of time as red giant stars. Medium red giant stars will eventually blow off their outer layers in a planetary nebula and then proceed towards the white dwarf stage.

A White Dwarf Star
Cold White Dwarf

The remaining hot, dense core is what makes up a white dwarf star. It is typically 180,000 degrees Fahrenheit (100,000 degrees Celsius), and 200,000 times as dense as the Earth. This means that a bit of white dwarf star the size of a sugar cube would weigh approximately 2,000 pounds on Earth.

Depending on the size of the original star, white dwarfs have different elements within their cores. Some scientists believe that certain white dwarfs likely have a layer of crystallized carbon within them that is reminiscent of a diamond.

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