The first detection of gravitational waves (ripples in the fabric of spacetime) in 2015 signaled the dawn of a new age of astronomical discovery. While only five gravitational wave detections have been announced so far, the most recent has answered several long-standing cosmic riddles.
Bursts of gamma rays, discovered in 1967, fall into two categories: short- and long-duration. The origin of short bursts in the mergers of neutron stars (hyper-collapsed stellar cores) remained hypothetical until August 17th, when gravitational waves were detected from two neutron stars spiraling together and exploding (a so-called “kilonova,” more energetic than a nova, but less than a supernova), producing a short gamma-ray burst.
Einstein predicted that gravitational waves should travel at the speed of light. The arrival of the gravitational waves and gamma rays from the August kilonova only 1.7 seconds apart after a 130 million year journey vindicated Einstein to one part in 300 trillion, simultaneously ruling out several competing theories of gravity.
The first major attempt to explain the relative abundance of the elements—from hydrogen through uranium, was published in 1957. It was a theoretical masterstroke, but left unanswered the origin of the heaviest elements, which exist in greater abundance than could be explained by known mechanisms (primarily, supernovae). Kilonovae were proposed as a solution in 1989, but none were observed until the Hubble Space Telescope caught one in 2013, in a galaxy too distant to detect definitive proof of its heavy element production.
When the gravitational waves of August’s much closer kilonova were detected, telescopes operating across the electromagnetic spectrum swung into action and showed that heavy elements are indeed produced in such events. The odds are good that any gold or platinum you own was produced in the collision of neutron stars billions of years ago.
Next column: The moon’s highest mountain.