Cosmic collisions forge heavy elements
The two neutron stars each have a diameter of only 20km, yet they still carry more mass than our entire Sun. As they collide, most of this mass in incorporated into a black hole, but the rest is ejected in a red-hot gas cloud. The cloud expands at one-third of the speed of light, growing from the size of a city to the size of the Solar System in just 36 hours.
Some 130 million years later, in 2017, no fewer than 70 observatories on seven continents all aimed their telescopes at this ‘kilonova’, forewarned by gravitational waves that had given astronomers 11 hours advance warning of a dramatic cosmic event. So
