Back when the Time Lord and I were still engaged, we went shopping for wedding rings. He only had one criteria: he wanted his ring to be made of platinum or a similar material forged in a supernova. It’s not quite as exotic as it sounds: most heavy elements were formed in supernovae, via a process called supernova nucleosynthesis.
Lighter elements form inside stars over the course of billions of years as they slowly burn through their fuel. But when massive stars use up their fuel — going from hydrogen to helium, to carbon, oxygen and so on — eventually there’s nothing left but iron and nickel. At that point, their cores collapse and they explode into supernovae. When that happens, heavier elements form within seconds — including gold, silver, lead, and uranium, as well as platinum — and are ultimately scattered throughout space, seeding the universe, so to speak.
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