Most of us know or have at least heard of White dwarfs, but the concept of Black Dwarfs is relatively newer and less heard off. A black dwarf is a hypothetical stellar remnant, created when a white dwarf becomes sufficiently cool so that it can no longer emit significant heat or light.
As we know, the stars whose mass is not too high become White Dwarfs in their final evolutionary state. Stars generate energy by the hydrogen fusion process. Once it’s mass is exhausted, this star expands into a red giant where helium is processed into carbon and oxygen. Technically, this process is known as triple-alpha process. Red giants must have sufficient mass to generate the core temperatures required to fuse carbon; an absence of the same will lead to the build up of inert mass of carbon and oxygen at its center. Such stars then expel their outer material, creating what is known as planetary nebula. Only the hot core of the star remains. This core then becomes a young white dwarf. When this white dwarf is made up of a dense ball of electron-degenerate matter, it cools slowly by thermal radiation, eventually becoming a black dwarf.
The time required for a white dwarf to actually cool down enough to the state of Black Dwarf is calculated to be longer than the current age of the universe which is that of 13.7 billion years. Hence, no black dwarfs are expected to exist in the universe. Also, Black dwarfs would emit almost no radiation and thus, it becomes extremely difficult to detect them practically. In spite of this, theoretically it is expected to be detected by gravitational influence.
(Black Dwarf Evolution)
Star -> Red Giant -> White Dwarf->Black Dwarf
