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.
In the early hours of New Year's Day, billions of miles from any Earthly celebrations, the New Horizons space probe swung by a small and extremely distant lump of ice and rock. It’s known to cataloguers as (486958) 2014 MU69, but the New Horizons team call it 'Ultima Thule' after the ancient expression for a place at the edge of the known world.
In a distant galaxy, long ago, a pair of black holes, each about thirty times more massive than our sun, began to orbit one another. Over the next several hundred million years, gravitational waves generated by their motion caused them to spiral together, slowly at first but gathering speed as they came closer and closer, until they were whirling about one another at the same rate as the blades in a kitchen blender. They eventually slammed together at about a third of the speed of light, emitting a last burst of gravitational waves before settling down to the sedate life of an ‘ordinary’ black hole.