Black holes normally reveal themselves in astronomy because they are surrounded by discs of gas, heated to high temperatures, stolen from nearby stars. The X-rays emitted from these accretion discs give away the black hole although it cannot itself be seen. But in the Large Magellanic Cloud is a star system called VFTS 243. There is a visible star of type O which is 160,000 times more luminous than the Sun and 25 times as massive - and that appears to be all. But spectroscopy reveals that the star is orbiting something unseen, which can only be a dormant black hole - that is, not feeding off its companion. This illustration shows the system but with the black hole's size exaggerated.