[In Depth] Gravitational waves serve up a mystery
For decades, physicists had claimed that the detection of gravitational waves—ripples in spacetime set off by cataclysmic events deep in space—would usher in a new type of astronomy and reveal new wonders. Last week, the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) delivered on that promise, as physicists announced the first detection of a gravitational signal—and, with it, a stellar surprise. The waves came from a pair of black holes spiraling together and colliding in space 1.3 billion light-years from Earth. Computer models showed that each was about 30 times as massive as our sun. That's about twice as massive as they should be, according to current theories of how black holes form from stars. Physicists hope more waves detected in the next few years will help them explain what is going on. LIGO should also provide new, rigorous tests of Einstein's general theory of relativity, and—working with...