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Category: Gold

The “Supernovas on steroids” that make gold

NASA astronomer and astrophysicist Dr. Michelle Thaller takes Glint through the phenomenal galactic explosions that make gold and reve...

29 August 2017

Alex Matchett

NASA astronomer and astrophysicist Dr. Michelle Thaller takes Glint through the phenomenal galactic explosions that make gold and reveals just how crucial the metal is to mankind

“My favourite fact in the entirety of human knowledge is that the Big Bang only produced the very simplest atoms. It produced hydrogen and helium, and that’s it,” says Dr Michelle Thaller getting straight to the first of a series of astounding fact bombs. Speaking from NASA’s HQ in Washington DC she begins the story of the cosmic chimes of the universe and how, now and again, they strike gold.

“The only thing in the universe that can make bigger atoms than hydrogen and helium is stars. Stars are nuclear fusion machines and, inside the core of a star, atoms are being rammed together to form bigger and bigger atoms. That’s how the star fuels itself, that’s why the sun shines. Think of your body — there’s water, carbon and oxygen; anything that isn’t hydrogen or helium had to be made inside a star and then that star had to explode and die.”

A depiction of a neutron star (copyright Kevin M Gill)

Standard stars such as our Sun can churn out most of the common elements such as nitrogen and carbon says Thaller, but it takes something very special to make anything “heavier” than iron: elements with lots of protons and neutrons. Those atoms have to be made specifically by a violently exploding massive star — a supernova explosion. “To make something like a gold atom you need unbelievably high temperatures, we’re taking in the trillions of degrees, entities that are pretty much unimaginable to us.”

Supernovas make some of the universe’s gold but the majority is now believed to come from a process even more cataclysmic: a gamma-ray burst. The name might not be quite as memorable but the science is no less astounding.

It starts with the leftover of a supernova explosion, either a black hole or a neutron star. The latter is the hyper-compressed core of the star says Thaller. “It’s the entire star crushed into something about 20 km across. The density is unimaginable, if you had a teaspoonful of this stuff it would have as much mass as Mount Everest and they rotate hundreds of times a second.”

Surprisingly, the phenomena of neutron stars are observed fairly regularly. Thaller sees “a couple a week” (although they remain rarer than supernovas, of which she sees about ten a night). NASA are looking to further their knowledge of these mysterious whirring powderkegs by sending an observational instrument called NICER (Neutron Star Interior Composition Explorer) to the International Space Station.

The NICER (Neutron Star Interior Composition Explorer) under construction (source: NASA)

The neutron stars that NICER will be observing are the cosmic ingredients of gamma-ray bursts. A gamma-ray burst is the colliding and epic exploding of two neutron stars, themselves each a product of a supernova. So most gold is forged in the furnace of not one, but three exploding stars.

A gamma-ray burst (source: NASA)

“When you have these neutron stars collide it’s like a supernova on steroids. If you look at the amount of heavy atoms coming off these things as they explode you can easily account for all the gold made in the universe,” says Thaller. So as the universe ages will these events become more common, making ever more gold? “That’s not necessarily true. The early universe had a greater production of these massive stars so gold production was probably greater then.”

The image of effervescent galactic furnaces spewing forth spectrums of light, energy and atoms at the dawn of time is made all the more incredible by the fact that it actually happened. From these fireworks of fusion came the gold we use to mark the value of so much here on Earth; but how did the metal travel from the far reaches of space to adorn the heads of sovereigns and the fingers of newly-weds?

Thaller explains the clouds of heavy atoms left by a gamma-ray burst formed nebulae from which new stars were born. “As the star forms it gravitationally bring all this material in, some of that stuff starts rotating in a disc and then planets form out of gravity on that disc. The dust clouds are full of every atom imaginable, including gold, so as gravity brought all these things together gold got built into the planets.” However, as a heavier element, gold invariably ended up at the centre of the planet. Thaller estimates there are 100 billion tonnes of gold sitting at the centre of the Earth alone.

So as the gold used on Tutankhamun’s funeral mask or on the Apollo astronauts’ helmets wasn’t mined from the centre of the Earth where did it come from? “Most of the gold that we can mine didn’t start here. There was a time in the Earth’s history called the Era of Heavy Bombardment when lots and lots of comets and asteroids reigned down on us. These asteroids have never been part of a larger body so these heavy elements remained intact. When they hit they left gold and other heavy elements in the crust of the Earth,” says Thaller.

The gold on astronaut Ed White’s, helmet helped shield him from solar radiation

So, from supernovas, to gamma-ray bursts, to asteroids, to Earth, to the ingot and then, for some gold, back into space as an invaluable element in mankind’s ongoing exploration. Thaller refers to another upcoming NASA project: the James Webb infra-red telescope, which will operate as a satellite and is set to launch next year. “The mirror is about seven times that of Hubble’s and it’s coated with gold.”

Gold is not only furthering our knowledge it seems, but critical to human evolution. Thaller reveals one final fact: “Our brains actually require a small amount of gold to work. It helps our neurons build and maintain an electrical charge. If you took all the gold out of the human body you wouldn’t be able to think.”

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Alex Matchett is editor of Glint

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