We don't think of space as a very wet place, but the cosmos is fairly awash in water in its solid, liquid and gaseous forms. That familiar truth, however, did not prepare two international teams of astronomers for what they discovered last summer: a black hole 20 billion times the mass of our sun surrounded by — and sucking in — a cloud of water vapor equivalent to 140 trillion times the mass of Earth's oceans. For sheer, jaw-dropping numbers you could stop there. But the scientists are using their discovery in an ingenious way: studying the swirl of the water cloud to make inferences about the structure of the black hole itself. Just like astronomers: no sooner do they discover something wonderfully, pointlessly cool than they find some practical way to use it.