Lijing Shao

Radio telescopes scattered across the globe pick up waves from distant black holes. But two telescopes placed almost side by side see only a blurry blob — fine details are beyond them. Usually, such pairs are considered useless and discarded. But that's a mistake: even a blurry blob holds clues.

At the center of our Galaxy lurks the supermassive black hole Sagittarius A* — a heavyweight that holds stars in its grip. Astronomers dream of finding pulsars near it: these cosmic lighthouses emit radio pulses with the precision of atomic clocks.

At the center of the Milky Way lies the supermassive black hole Sagittarius A*. It is four million times more massive than the Sun, but by cosmic standards it behaves quietly: it only occasionally flares up when it swallows a clump of gas.

A pair of figure skaters spins while holding hands. If their path is a perfect circle, each push from a partner is predictable. But stretch that path into an oval, and the effort becomes uneven: a jerk as they come together, a lull as they pull apart. Something similar happens with two black holes in the final minutes before they merge.