They concluded that 1.3 billion years ago, a time when multicellular life was just starting to coalesce on planet earth, two distant black holes were orbiting each other ever more closely and ever more quickly, closing in on the speed of light, until in a final orbital frenzy they smashed together. The collision generated a tidal wave in space, a gravitational tsunami so enormous that its power exceeded that produced by every star in every galaxy in the observable universe.
