Doona was a star located in the galaxy's Alpha or Beta Quadrants, in or near the Alpho Galaxy region of space. When it became a supernova, a piece of it somehow escaped destruction. It weighed ten thousand tons, was ten times harder than diamond, and radiated a repelling force. Vulcan scientists studied the phenomenon for centuries.
In 2266, the USS Enterprise used magnetic force to tow the former star to the point where the planets Morti and Inicrust were about to collide, the repelling force preventing the destruction of both worlds and their inhabitants. (TOS comic: "When Planets Collide")