What is a white dwarf made of?

A white dwarf is made of a dense core of carbon and oxygen surrounded by a thin layer of helium and hydrogen.

White dwarfs are the remnants of low to medium mass stars that have exhausted their nuclear fuel and shed their outer layers. The core of a white dwarf is incredibly dense, with a mass comparable to that of the sun but a radius only about the size of the Earth. This density is due to the fact that the electrons in the core are packed tightly together, creating a degenerate electron gas that supports the weight of the star.

The core of a white dwarf is primarily composed of carbon and oxygen, which are the end products of nuclear fusion in the star's core. These elements are so tightly packed that they are no longer able to undergo fusion, which is why the star has stopped producing energy and is no longer shining.

Surrounding the core of a white dwarf is a thin layer of helium and hydrogen, which were the outermost layers of the star before it shed them. These layers are relatively cool and do not contribute much to the overall luminosity of the star. However, they can be heated up if the white dwarf is in a binary system and is accreting matter from a companion star, leading to explosive phenomena such as novae and supernovae.