Black dwarf

A black dwarf is a hypothetical stellar remnant formed when a white dwarf cools until it emits negligible light. The universe is not yet old enough for any to exist.

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White dwarf: A dense stellar remnant supported against gravity by electron degeneracy pressure. A black dwarf is the hypothetical cooled endpoint of this remnant.
Stellar evolution: The sequence of physical changes a star undergoes over its lifetime. It explains how stars reach the white-dwarf stage that can later cool into black dwarfs.
Black hole: A region of spacetime whose gravity prevents anything, including light, from escaping beyond its event horizon. Unlike a black dwarf, a black hole is dark because light cannot escape, not because a remnant has cooled.
Stelliferous era: The cosmological era during which stars form and shine. Black dwarfs belong to the far-future transition out of the era of shining stars.
White dwarf cooling: The gradual loss of thermal energy and luminosity by a white dwarf. Continued cooling is the process that would produce a black dwarf.
Red giant: A luminous, expanded late-life phase of a low- or intermediate-mass star. The progenitor sheds its outer layers after expanding into this phase.
Brown dwarf: A substellar object too low in mass to sustain ordinary hydrogen fusion in its core. A brown dwarf is a failed star-like object, not a cooled stellar remnant.
Degenerate era: A proposed far-future era dominated by stellar remnants and other degenerate objects. Black dwarfs would be among its enduring stellar remnants.
Electron degeneracy pressure: Pressure arising from the quantum mechanical restriction that identical electrons cannot occupy the same state. It supports the white dwarf after nuclear burning ends, while the remnant cools.
Planetary nebula: An expanding shell of gas ejected by a dying low- or intermediate-mass star. Its dispersal exposes the stellar core that becomes a white dwarf.