An Alchemical Explosion

(Image:Artist’s illustration of two merging neutron stars. The rippling spacetime grid represents gravitational waves traveling out from the collision, while the narrow beams show bursts of gamma rays expelled just seconds after the gravitational waves. Ejected clouds of glowing, neutron-rich material swirl around the merging stars. Credit: NSF/LIGO/Sonoma State University/A. Simonnet)

Scientists at LIGO have detected, for the first time, spacetime ripples known as gravitational waves from the collision of two neutron stars. This phenomenon was predicted by Einstein but had not been observed until August 17 2017. All of the previously detected gravitational waves came from merging pairs of black holes which are so dense that light cannot escape their grasp, making such mergers essentially invisible to normal telescopes. While neutron stars appear to create less extreme gravitational force than that generated by black holes, these super-dense stars created by the collapse of supernova, have gravitational fields strong enough to squeeze and break down an entire sun into a ball of neutrons the size of a small city. Unlike a black hole, a neutron star’s gravity is too weak to trap light, meaning the huge burst made from two of them slamming together can be bright enough to be observed from Earth.

The collision of these two neutron stars likely produced a black hole, allowing the observation of the birth of one of these phenomena. It also provides evidence that it is neutron star collisions that forge the universe’s heavy elements including uranium, platinum and gold. The bulk of the universe’s hydrogen and helium was produced in the first moments after the big bang, and most of the lighter elements—oxygen, carbon, nitrogen etc—were formed from nuclear fusion in stars, but scientists were unsure as to the origin of the heavier elements. This new cosmic observation provides evidence that the collision of the universe’s densest stars is the true alchemical forge.

“If you think about it, the universe is sort of a cosmic particle collider, with neutron stars as the particles,” O’Shaughnessy says. “It throws them together, and we now have the opportunity to see what comes out…. This event is a Rosetta stone, giving us real data to connect disparate threads of astrophysics that previously only existed in the mind of theorists or as bits in a supercomputer simulation. It allows us to understand the cosmic abundance of heavy elements. It allows us to probe the squishiness of nuclear matter at extreme densities. It allows us to measure the expansion of the universe…. We are now reaping the reward, a mountain of gold 10 or a hundred times the mass of the Earth, that the universe just gave us.”

Richard O’Shaughnessy, an astrophysicist and LIGO team member at Rochester Institute of Technology quoted in Scientific American. (