What is a black dwarf star

Black dwarf

In principle, black dwarfs refer to cooled white dwarfs, i.e. compact objects that have cooled down over such a long period of time that they no longer even radiate significantly thermally. However, it should be noted that thermodynamics forbids reaching absolute zero (0 Kelvin) in the formulation of the third law of thermodynamics.

Are there black dwarfs?

Astrophysicists have theoretically derived the cooling time scale of white dwarfs and have found time scales in the range of Billions of years! This is just a timescale on which the universe developed (world age almost 14 billion years, Hubble time). It is therefore not to be expected that a particularly large number of black dwarfs (in this narrow definition as successors of white dwarfs) exist.

Difference to brown dwarfs

Black dwarfs are to be distinguished from brown dwarfs because the latter are not able to ignite the thermonuclear fusion processes and are more like planets. While black dwarfs have the 'normal life' of a star behind them, it has not even begun in brown dwarfs.

Meaning for cosmology?

Black dwarfs are a form of baryonic dark matter. The current data of experimental cosmology see baryonic matter as a form of energy that is not of great importance for the dynamics of the universe. The black dwarfs cannot solve the missing mass problem of cosmology on their own.