The Mysterious Origin of Our Galaxy’s Gold

Across history and folklore, the question of where Earth’s gold came from—and maybe how to get more of it—has invited fantastical explanation. The Inca believed gold fell from the sky as either the tears or the sweat of the sun god Inti. Aristotle held that gold was hardened water, transformed when the sun’s rays penetrated deep underground. Isaac Newton transcribed a recipe for making it with a philosopher’s stone. Rumpelstiltskin, of course, could spin it from straw.

Modern astrophysicists have their own story. The coda, at least, is relatively clear: About four billion years ago, during a period called the “late veneer,” meteorites flecked with small amounts of precious metals—gold included—hammered the nascent Earth. But the more fundamental question of where gold was forged in the cosmos is still contentious.

For decades, the prevailing account has been that supernova explosions make gold, along with dozens of other heavy elements on the bottom few rows of the periodic table. But as computer models of supernovas have improved, they suggest that most of these explosions do just about as well at making gold as history’s alchemists. Perhaps a new kind of event—one that has traditionally been difficult, if not impossible, to study—is responsible.

In the past few years, a debate has erupted. Many astronomers now believe that the space-quaking merger of two neutron stars can forge the universe’s supply of heavy elements. Others hold that even if garden-variety supernovas can’t do the trick, more exotic examples might still be able to. To settle the argument, astrophysicists are searching for clues everywhere, from alchemical computer simulations to gamma-ray telescopes to the manganese crust of the deep ocean. And the race is on