Dawn of an Era: Astronomers Hear and See Cosmic Collision

Two neutron stars merge into a kilonova. (Credit: Illustration by Robin Dienel, courtesy of the Carnegie Institution for Science) For hundreds of millions of years, two city-sized stars in a galaxy not-so-far away circled each other in a fatal dance. Their dimensions were diminutive, but each outweighed our sun. They were neutron stars — the collapsed cores left behind after giant stars explode into supernovas. Closer and closer they spun, shedding gravitational energy, until the stars traveled at nearly the speed of light, completing an orbit 100 times every second. By then, dinosaurs reigned on Earth, and the first flowers were just blooming. That's when, 130 million years ago, the dance ended. The collision was fast and violent, likely spawning a black hole. A shudder — a gravitational wave — was sent out across the fabric of space-time. And as the stars' outer layers launched into space, the force formed a vast cloud of subatomic particles that would cool into many Earths' worth of gold, platinum and uranium. Seconds later, a blast of high-energy gamma-rays – the most energetic kind of light – punched through the erupting cloud. The space-time ripple and the light crossed the cosmos together, and finally arrived at 6:41 a.m. Eastern on Aug. 17. The gravitational wave first reached Italy's freshly finished detector Advanced Virgo before stretching and squeezing the lasers at America's two LIGO sites. Two seconds later, NASA's gamma-ray detecting Fermi spacecraft caught the blast. In the weeks since, hundreds of astronomers on all seven continents have turned their telescopes and spacecraft to watch the cosmic collision play out in all manner of light – radio, infrared, optical, ultraviolet, X-rays, gamma-rays. The Spitzer and Hubble space telescopes are still watching the event, as is the Very Large Array in New Mexico. Right now, it’s the greatest show in astronomy. “What was surprising with this one was it was extremely close to us, and so it was an extremely strong signal,” says LIGO scientist Jolien Creighton of the University of Wisconsin-Milwaukee. “We were figuring with our full Advanced LIGO sensitivity we might see something like this every few years.”