Black holes have a fearsome reputation. They have imperilled a thousand stricken starship crews in the pages of science fiction, and the language used to describe them even in non-fiction often implies menace. In popular science, they ‘lurk’ at the centres of galaxies, waiting to ‘devour’ passing stars. I’m not sure this sort of imagery is justified, though it can be hard to avoid. A lot of the time black holes are passive, quiet beasts.