What is a white dwarf?

A white dwarf is a type of star that forms after a main sequence star has exhausted the nuclear fuel in its core and has shed its outer layers. The remaining core then collapses under gravity, and the star's outer layers are ejected into space in a planetary nebula. The white dwarf is what remains of the core, and it is incredibly dense. In fact, a teaspoonful of a white dwarf would weigh about as much as an elephant.

White dwarfs are typically about the size of the Earth but can have masses similar to that of the Sun. They are very hot and can have surface temperatures of up to 100,000 Kelvin. However, they are not powered by nuclear fusion like other stars, but instead, they simply radiate away the heat left over from their formation. As a result, they gradually cool down and become dimmer over time, eventually becoming black dwarfs.

White dwarfs were first discovered in the mid-19th century, and they have since been studied extensively. They play an important role in the evolution of stars, and they are also used to study the age of the Milky Way galaxy.