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There’s too much gold in the universe. No one knows where it came from

Here’s what’s wrong: Gold is an element, so it can’t be made through normal chemical reactions, even though alchemists tried for hundreds of years. To make the sparkly metal, you have to combine 79 protons and 118 neutrons into a single atomic nucleus. There is a lot of nuclear fusion going on there. But this kind of intense fusion doesn’t happen often enough, at least not close enough, to make the huge amounts of gold we find on Earth and in other parts of the solar system.

And a new study has found that the most common idea about where gold comes from — that it comes from collisions between neutron stars — doesn’t work either. So, where does all the gold come from? Some other possibilities include supernovas that are so powerful that they turn a star inside out. The new study finds that even such strange things can’t explain how blinged out the local universe is.

A picture shows what happens when two neutron stars crash into each other. Scientists had thought that these kinds of collisions might have made our solar system full of gold, but new research calls that idea into question. NASA/Swift/Dana Berry took this picture. Gold is falling from the sky everywhere. Nobody knows what it is, though.

Neutron star collisions make gold by smashing protons and neutrons together for a short time to form atomic nuclei. These newly formed heavy nuclei are then shot out into space. Chiaki Kobayashi, an astrophysicist at the University of Hertfordshire in the UK and the lead author of the new study, said that regular supernovas can’t explain the gold in the universe because stars that are big enough to fuse gold before they die are rare, and when they explode, they turn into black holes. In a normal supernova, the gold gets sucked into the black hole.

So what about those strange supernovas where stars flip over? This type of star explosion, called a magneto-rotational supernova, is “a very rare supernova that spins very fast,” Kobayashi told Live Science.

During a magneto-rotational supernova, a dying star spins so fast and is hit by such strong magnetic fields that it turns itself inside out as it explodes. As the star dies, it sends out jets of white-hot matter into space. And since the star is now on its back, its jets are full of gold nuclei. Gold-fusing stars are not very common. Even less common are stars that can fuse gold and send it out into space like this.

But Kobayashi and her team found that even neutron stars and magneto-rotational supernovas together can’t explain why Earth has so much gold.

“This question has two parts,” she said. “Number one is that merging neutron stars is not enough. Even with the second source, we still can’t explain the amount of gold that has been found.

She said that it was true that when two neutron stars collide, they send out a shower of gold. But these studies didn’t take into account how rare these accidents are. It’s hard to say exactly how often tiny neutron stars, which are the ultradense leftovers of supernovas from long ago, crash into each other. But it doesn’t happen very often. Scientists have only ever seen it happen once. Kobayashi and her co-authors found that even rough estimates show that they don’t crash together nearly often enough to have made all the gold in the solar system.

“This question has two parts,” she said. “Number one is that merging neutron stars is not enough. Even with the second source, we still can’t explain the amount of gold that has been found.

She said that it was true that when two neutron stars collide, they send out a shower of gold. But these studies didn’t take into account how rare these accidents are. It’s hard to say exactly how often tiny neutron stars, which are the ultradense leftovers of supernovas from long ago, crash into each other. But it doesn’t happen very often. Scientists have only ever seen it happen once. Even rough estimates show they don’t collide nearly often enough to have produced all the gold found in the solar system, Kobayashi and her co-authors found.

“This paper is not the first to suggest that neutron star collisions are not enough to explain why gold is so common,” said Ian Roederer, an astrophysicist at the University of Michigan who looks for rare elements in stars far away.

Roederer said that the new paper by Kobayashi and her colleagues, which was published in The Astrophysical Journal, has one big plus: it is very thorough. The researchers looked at a huge amount of data and used it to build strong models of how the galaxy changes and makes new chemicals.

“The paper refers to 341 other publications,” Roederer told Live Science. “This is about three times as many references as a typical paper in The Astrophysical Journal has these days.”

He said that making sense of all that information would take a “Herculean effort.”

With this method, the authors were able to explain how atoms like carbon-12 (which has six protons and six neutrons) and uranium-238 were made (92 protons and 146 neutrons). Roederer said that was an impressive range, because it included things that are usually left out of these kinds of studies.

Most of the time, the math was right.

In their model, strontium was made when neutron stars hit each other. Scientists have seen strontium in space after one neutron star collision. This matches what they have seen.

Magneto-rotational supernovas did explain why their model had europium, which had been hard to explain in the past.

But gold is still a mystery.

Kobayashi said that something out there that scientists don’t understand must be making gold. Or, it’s possible that when neutron stars collide, they make a lot more gold than models show. Astrophysicists still have a lot of work to do before they can explain where all that fancy bling came from.


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