Where does gold come from? The stars!

Where gold originates from has been a question for the ages. Alchemists have been trying to create it from existing metals, but the only places you can get it are to dig it out of the Earth and pan it in rivers. But that doesn’t explain how it’s actually “made”. Well, late last year, we found out how.

On 17 August 2017, a cataclysmic event trillions of miles away from Earth resulted in two stunning things: 1) the first detectable burst of gravitational waves; and 2) an explanation of how gold is “made”.

The cataclysm, the results of which so many observatories around the world witnessed on that and following days, was the “collision” between (merging of) two neutron stars in the galaxy NGC 4993, located in the constellation Hydra, about 130 million light years from Earth.

Apart from making (gravitational) waves, when these particular balls of pure neutrons (each about 10 kilometres wide and each with a mass equivalent to that of our sun) collided, amongst the other heavy elements created in the explosion, and shot every which way into surrounding space as a huge cloud of gas, were an estimated six billion trillion metric tons of pure gold. Or about the same mass as the Earth!

A (Neutron) Stellar Collision!¹

Source: NASA Goddard Space Flight Center/CI Lab

Unfortunately, none of this gold is going to end up on Earth in our lifetime, if ever. Instead it will, over forthcoming eons, become just some of the substance of new stars, planets, moons, and other heavenly bodies.

The question, then, is: If these collisions have been going on for billions of years, why is there so little gold on Earth to be dug up or panned? Surely there should be more of it around—indeed a great deal more. 

The answer’s a really interesting one. When you subtract what’s thought to lie in the Earth’s outer crust and underlying rocky mantle from the gold that should actually be in Earth, some 99% does, indeed, appear to be “missing.”

While you may be thinking that it’s nearly impossible to misplace roughly 2,000 trillion metric tons of gold, Professor Bernard Wood of the Department of Earth Sciences at the University of Oxford provided us the logical explanation (and a reminder of the importance of prepositions). Although technically the missing gold may not be on Earth, it’s actually in the Earth - not as a massive nugget to be discovered, but in its core and, therefore, inaccessible.

But how it got there is equally as interesting. Professor Wood once again provided us with the answer. Gold is very soluble in iron. When it was forming, the Earth was still a ball of molten iron, and other metals, and as its iron-rich core separated from both the mantle and crust, it dissolved the gold, and other noble metals, and took them with it to the center of the Earth. Where it, and they, have remained ever since.