Is there such a thing as a black dwarf Does such a heavenly body exist called a black dwarf? It would be a Brown dwarf that has cooled to the point it no longer gives off heat or light.
A black dwarf is a white dwarf that has cooled to the point that it is no longer emitting light. However it takes a long time for a white dwarf to cool down. The exact timescale is rather uncertain, but at least hundreds of billions of years, perhaps hundreds of trillions of years. 

The upshot is that that no black dwarfs exist in the universe today. The Universe is only about 14 billion years old, so there hasn't been time for any black dwarfs to form.

The paper A Dying Universe: The Long Term Fate and Evolution of Astrophysical Objects discusses brown dwarfs, black dwarfs, and other objects that may exist in an aging universe.