The origin of platinum and gold is every bit as storied and exotic as the metals themselves, says astrophysicist Stephan Rosswog of the University of Leicester in England. These precious elements arise during one of the rarest and most violent events in the cosmos: the cataclysmic merger of two neutron stars, ultradense stellar remnants that pack the mass of half a million Earths into a ball the size of Manhattan.
Astronomers have long understood that nuclear fusion in stars creates middleweight elements such as carbon and oxygen, but these reactions cannot create superheavy platinum and gold. Rosswog therefore started investigating the far more intense conditions that arise when two orbiting neutron stars spiral in toward each other. "In the beginning it is a very slow process, lasting 100 million years or more. But the last 100 kilometers [about 60 miles] or so before they merge is violent and fast, lasting less than half a second," he says. New supercomputer simulations devised by Rosswog and his colleagues (shown above) indicate that a great deal of nuclear alchemy occurs during the last few milliseconds.
The merger unleashes so much energy that it briefly outshines anything else in the universe. Most of the material quickly collapses into a black hole, but some of it spews out in a flood of superhot neutrons and atomic nuclei. The nuclei rapidly mop up the stray neutrons, forming heavy elements such as lead, gold, and platinum. Although neutron-star collisions occur just once every 100,000 years in a typical galaxy, that's often enough to account for all of the precious metals on Earth.
|Courtesy of S. Rosswog and R. West|