Nature: For years it has been suspected that astronomers would never see the heart of a black hole. These singularities — where the known laws of physics break down — would be hidden by the 'event horizon', a boundary beyond which light cannot escape from the black hole's gravitational pull, insulating the object from the universe.

However, theoretical physicists, such as Arlie Petters of Duke University in Durham, North Carolina, and Marcus Werner of the University of Cambridge, UK, recently proposed that if the black hole rotates fast enough, the singularity would be detectable because they act as very strong 'gravitational lenses', bending the light coming from stars behind them by their distortion of space-time. Current telescopes should be able to detect such events they say.

Now George Matsas and André da Silva of the São Paulo State University in Brazil suggest a mechanism to explain how a black hole could get fast enough to be visible: quantum mechanics. An electrically charged black hole spinning fast enough to be right on the brink of losing its event horizon might be pushed over the edge by gaining angular momentum from quantum particles that could tunnel inside the event horizon says Philip Ball, who describes the research in this week's Nature.