Black star

A black star was a star made of quasi-baryonic dark matter. Since it was only partially real it could become more massive than a black hole, without actually collapsing out of real-space. Moreover, such a star didn't give out any energy signature,      which made them almost impossible to detect, and its semi-tachyonic nature made it a danger to the temporal vortex as well. (PROSE: Sanctuary)

During the Sontaran invasion of Gallifrey, Borusa ordered Andred to drive the Fourth Doctor's TARDIS, by then President-elect, into a black star, in vain. (TV: The Invasion of Time)