A black dwarf was a rare compact star and one endpoint of stellar evolution. White dwarf stars that were once giant stars decayed into black dwarfs after burning all of their fuel and then cooling. "The Ring," a black dwarf surrounded by highly ionized, radioactive green gas, could be found in the Outer Rim's Anoat sector.
A black dwarf was a type of dwarf star classified as a compact star, representing the endpoint of stellar evolution. A giant star that exhausted all of its hydrogen fuel could collapse into a white dwarf, which in very rare instances—making for less than one percent of all stars in the galaxy—could then become a black dwarf as the core of the star cooled. Remnant dust clouds with unusual chemical elements could potentially coalesce around the area of the star. Black dwarfs were unlikely to support life.
Eons before the Galactic Civil War, which was fought between the Galactic Empire and the Rebel Alliance between 2 BBY and 4 ABY, a star located in the Anoat sector of the Outer Rim Territories exploded and eventually decayed into a black dwarf. Locals of the Greater Javin region knew this star as "the Ring" for the highly ionized, radioactive green gas that surrounded it. What remained of the Ring's supernova took shape as the Twin Nebulae, vast clouds of glittering gas and dust that for centuries hampered regional hyperspace exploration.
Behind the scenes
The 1993 West End Games sourcebook Galaxy Guide 8: Scouts, part of Star Wars: The Roleplaying Game, first introduced the concept of black dwarfs to the Star Wars universe. "Galactic Gazetteer: Hoth and the Greater Javin," a 2004 supplement for Wizards of the Coast's Star Wars Roleplaying Game, later established the existence of the Ring, the only example of a black dwarf in the Star Wars Legends continuity. The subsequent 2009 reference book The Essential Atlas mapped out the black dwarf's placement in the Star Wars version of stellar evolution, which mirrors the real-world equivalent, including the stages of the main sequence.
In real-world astronomy, a black dwarf is the theoretical endpoint of stellar evolution, wherein a white dwarf has cooled sufficiently that it no longer emits visible light. Scientists do not expect that any black dwarfs yet exist in the universe, since the calculated time for a white dwarf to transition into a black dwarf exceeds the current age of the universe, at nearly 14 billion years.