On September 14, 2015, lasers underground in Louisiana and Washington State wavered together in response to a disturbance in spacetime, and a new window opened onto the cosmos. The two sites are part of the LIGO gravitational-wave detector—sensitive, powerful lasers so carefully isolated from Earth's motion that they can pick up incredibly minuscule vibrations. The signal was a gravitational wave, a ripple in spacetime created by two black holes merging 1.4 billion light-years away, far beyond our Milky Way galaxy. The event—the first detection of gravitational waves—also proved that black holes can orbit each other and merge. Since then, sensors have detected 43 more events, making them seem almost commonplace, says Christopher Berry, a member of the LIGO team. The accumulating data are helping astronomers better understand the menagerie of objects that populate the universe.