![]() To make heavy elements more reliably, you can bombard iron nuclei with charge-free neutrons. Nuclei bigger than iron are so positively charged, and so difficult to bring together, that fusion no longer returns more energy than you have to put in. But the process stops at iron, which is among the most stable elements. Stars then fused these elements into progressively heavier elements. The Big Bang left behind hydrogen, helium, and lithium. “Kind of like you squeeze a tube of toothpaste, stuff comes flying out the end.” “The problem itself is rather old, and now for a long time has been the last stardust secret,” said Anna Frebel, an astronomer at the Massachusetts Institute of Technology. That implied that humans, or at least the elements making up our bodies, were once stardust. In 1957, the physicists Margaret and Geoffrey Burbidge, William Fowler, and Fred Hoyle laid out a set of recipes for how the lives and deaths of stars could fill in almost every slot in the periodic table. And the race is on to make an observation that would seal the deal-catching one of the cosmos’s rarest mints with its assembly line still running. 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. Others hold that even if garden-variety supernovas can’t do the trick, more exotic examples might still be able to. ![]() Many astronomers now believe that the space-quaking merger of two neutron stars can forge the universe’s supply of heavy elements. In the past few years, a debate has erupted. Perhaps a new kind of event-one that has traditionally been difficult, if not impossible, to study-is responsible. 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. But the more fundamental question of where gold was forged in the cosmos is still contentious.įor 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. 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. Modern astrophysicists have their own story. Rumpelstiltskin, of course, could spin it from straw. Isaac Newton transcribed a recipe for making it with a philosopher’s stone. Aristotle held that gold was hardened water, transformed when the sun’s rays penetrated deep underground. The Inca believed gold fell from the sky as either the tears or the sweat of the sun god Inti. 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.
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