A white dwarf is a star formed when a red giant runs out of helium fuel after losing most of its mass into space.

In 2364, the SS Tsiolkovsky was observing the formation of a white dwarf when its crew succumbed to polywater intoxication. The USS Enterprise-D, sent to investigate, was subsequently threatened by a stellar core fragment thrown off by the collapse of the red giant. (TNG: "The Naked Now")

White dwarfs are the only natural source of vertion particles. In 2370, a network emergent circuit nodes aboard the Enterprise-D collected vertions from the white dwarf Tambor Beta-6 to sustain their growth, but the supply from a single star proved insufficient. (TNG: "Emergence")

A white dwarf is a dim, dense, planet-sized star that marks the evolutionary endpoint for all but the most massive stars. The first white dwarf to be discovered, in 1862, and the closest to the Sun, is the companion of Sirius.

White dwarfs form from the collapse of stellar cores in which nuclear fusion has stopped, and are exposed to space following the loss of the old star's bloated outer envelope, typically as a planetary nebula. They consist of electron degenerate matter, which provides the pressure needed to prevent further collapse, providing that the mass of the dwarf doesn't exceed the Chandrasekhar limit of about 1.4 solar masses. Even a fairly large white dwarf, with a mass similar to that of the Sun, is only about as big as Earth.