Where gold comes from: following an element's cosmic history

Gold's place in jewellery is familiar; its formation is less so. Tracing that history takes the discussion from chemistry to events far beyond Earth.

Ancient alchemists dreamed of turning stone into gold, but they were destined to fail. Because they didn't know a brutal physical fact: No chemical reaction on Earth can create gold.

Even the massive sun above our heads can't do it.

The sun is a giant nuclear fusion reactor. Every day, it squeezes Hydrogen into Helium, releasing light and heat in the process. But the sun is too "cold." Its core temperature can only create light elements like Carbon and Oxygen. To create heavy gold atoms (Atomic Number 79), the sun falls far short.

In the laws of the universe, only death can create something greater.

Massive stars, dozens of times larger than the sun, possess greater power. Like mad craftsmen, they fuse elements layer by layer, getting heavier and heavier: Hydrogen ➔ Helium ➔ Carbon ➔ Neon ➔ Oxygen ➔ Silicon...

Until one day, they create Iron (Fe).

Iron is the curse of the star. It is the most stable element in the universe. Fusing iron no longer produces energy; instead, it consumes energy. When a star's heart fills with iron, the fire of nuclear fusion instantly goes out. The star "dies."

It collapses under gravity, yet even in its final supernova explosion, it struggles to produce significant amounts of gold.

So, where does gold come from? The answer lies between two dead stars.

When two massive stars die, they may become Neutron Stars. These stars are terrifyingly dense; a piece the size of a sugar cube would weigh 1 billion tons.

If these two lonely dead stars meet under the pull of gravity, they begin a deadly waltz. They spin, get closer, faster and faster, until finally—they collide.

This is a cosmic-level collision known as a "Kilonova." [Image of neutron star collision kilonova]

In that instant, extreme temperatures and neutron flux trigger the "r-process" (rapid neutron capture process). Iron atoms are violently stuffed with neutrons, instantly "fattening up" to become heavy metals like Gold and Platinum.

This is not a disaster, but a grand seeding. This explosion scatters hundreds of Earth-masses of gold into deep space.

An account of how gold can form is different from knowing the precise history of a particular ring. Keep the formation process and the history of a sample separate when moving from astronomy to jewellery.