Graphic: Hearing a passing ripple in space-time:
Predicted by Einstein's general theory of relativity 100 years ago, gravitational waves have been directly detected for the first time. LIGO, the Laser Interferometer Gravitational-Wave Observatory, heard black holes colliding.
TWO BLACK HOLES
About 1.2 billion years ago in a distant galaxy, a pair of black holes circled each other. The larger black hole was 36 times the mass of our sun, and the smaller one 29 times.
COLLISION
The intense gravity accelerated the black holes to half the speed of light, pulling them closer and carving distortions in space and time. In a fraction of a second, the pair collided and merged into an irregular shape.
RING DOWN
The unstable blob smoothed itself into a sphere, a process called “ring down.” Three solar masses’ worth of energy were vaporized in a storm of gravitational waves, distorting space and time and leaving a new black hole 62 times the mass of the sun.
GRAVITATIONAL WAVES
The invisible waves rippled outward at the speed of light. But waves fade with distance, and when they finally reached Earth, the distortions were too small to be measured above the heat, noise and other vibrations of our planet.
LIGO
is a pair of L-shaped observatories 1,900 miles apart. Ultra-pure mirrors at the ends of each arm are isolated from vibrations. Passing gravitational waves push and pull the arms, changing the length of tunnels by less than the width of a proton.
A CHIRP
On Sept. 14, LIGO’s detectors measured their first vibrations from a gravitational wave. Translated to sound, it was a short chirp, the billion-yearold echo of the collision of those two black holes