The stars orbited each other like a pair of dancers, their sequined costumes glowing against a dark stage. Round and round they went, until the distance between them began to shrink. The closer they got, the faster they spun. And then, smack! The stars collided.
About 500 million years later, Mansi Kasliwal’s phone rang in the middle of the night in April. “Dear human,” a robotic voice said when she picked up. “You have received a new gravitational-wave alert.”
The signal from the cosmic dance had reached her at last.
Kasliwal, an astronomy professor at Caltech, jumped out of bed. Gravitational waves are ripples in the very fabric of the universe. It sounds bizarre, but space is elastic, and can be bent, warped, and squished. These gymnastics require some extremely powerful motions, such as the furious spinning of massive astrophysical objects. Their rotation is so intense that it sends waves coursing through the universe at the speed of light. The ripples move through everything they pass—galaxies, stars, even planets. And when they reach us, ultrasensitive instruments are now waiting to detect them.
Research stations broadcast the detections to astronomers such as Kasliwal and her team at Caltech, a rapid-response group trained to respond to sudden and intriguing observations in the night sky. When she gets the call, Kasliwal commandeers telescopes around the world to drop what they’re doing and search for the origin of the gravitational waves. The ripples are invisible, but sometimes cosmic collisions give off light. Astronomers can learn a lot more if they see that.