There’s too much gold in the universe. No one knows where it came from.
Something is raining gold down on the universe. No one knows what it is.
Here’s the problem: gold is an element, which means you can’t make it through ordinary chemical reactions — though alchemists tried for centuries. To make the sparkly metal, you have to bind 79 protons and 118 neutrons together to form a single atomic nucleus. That is a powerful nuclear fusion reaction. However, such powerful fusion does not occur frequently enough, at least not nearby, to produce the enormous amounts of gold found on the Earth and elsewhere in the solar system. A new study has discovered that the most commonly accepted origin of gold – collisions between neutron stars — cannot explain gold’s abundance either. So, where does the gold come from?
Other possibilities include supernovas that are so powerful that they turn a star inside out. According to the new study, even such strange phenomena can not explain how blinged out the local universe is.
Neutron star collisions generate gold by briefly colliding protons and neutrons into atomic nuclei and then expelling those newly-bound heavy nuclei into space. Regular supernovas can’t explain the universe’s gold because stars massive enough to fuse gold before they die — which are rare — become black holes when they explode, said Chiaki Kobayashi, an astrophysicist at the University of Hertfordshire in the United Kingdom and lead author of the new study. In a typical supernova, the gold is pulled into the black hole.
So, what about the more rare, star-flipping supernovas? This type of star explosion, known as a magneto-rotational supernova, is “a very rare supernova, spinning very fast,” according to Kobayashi.
During a magneto-rotational supernova, a dying star spins so fast and is wracked by such strong magnetic fields that it turns itself inside out as it explodes. The dying star releases white-hot jets of matter into space. Because the star has been turned inside out, the jets are filled with gold nuclei. Stars that fuse gold at all are rare. Stars that fuse gold and hurl it into space are much more rare.
However, even neutron stars and magneto-rotational supernovae cannot explain Earth’s gold rush, as according Kobayashi and her colleagues.
“There’s two stages to this question,” she said. “Number one is: neutron star mergers are not enough. Number two: Even with the second source, we still can’t explain the observed amount of gold.”
Past studies were right that neutron star collisions release a shower of gold, she said. However, such studies did not take into consideration the rarity of those collisions. It’s difficult to say how often small neutron stars meet — themselves ultra-dense remnants of previous supernovas. But that’s not very common: scientists have only seen it happen once. Even rough estimates show that they don’t collide nearly frequently enough to produce all of the gold found in the solar system, according to Kobayashi and her co-authors.
“There’s two stages to this question,” she said. “Number one is: neutron star mergers are not enough. Number two: Even with the second source, we can’t explain the amount of gold observed.”
Previous research has shown that neutron star collisions generate a gold shower, she says. Nevertheless, such studies did not take into consideration the rarity of those incidents. It’s difficult to say how often small neutron stars meet — themselves ultra-dense remnants of previous supernovas. But that’s not very common: scientists have only observed it happen once. Even rough estimates show that they don’t collide nearly frequently enough to produce all of the gold found in the solar system, according to Kobayashi and her co-authors.
“This paper is not the first to suggest that neutron star collisions are insufficient to explain the abundance of gold,” said Ian Roederer, an astrophysicist at the University of Michigan, who hunts traces of rare elements in distant stars.
However, Kobayashi and her colleagues’ new paper, published on September 15 in The Astrophysical Journal, has one strong benefit: it is extremely thorough, according to Roederer. The researchers poured over a mountain of data and plugged it into robust models of how the galaxy evolves and produces new chemicals.
“The paper contains references to 341 other publications, which is about three times as many references as typical papers in The Astrophysical Journal these days,” Roederer told Live Science.
He described gathering all of that data in an useful way as a “Herculean effort.”
The authors were able to explain the formation of atoms as light as carbon-12 (six protons and six neutrons) and as heavy as uranium-238 using this method (92 protons and 146 neutrons). That’s an impressive range, according to Roederer, covering elements that are typically ignored in these types of studies.
The math mostly worked out.
Strontium was produced in their model via neutron star collisions, for example. That matches to strontium observations in space following the one neutron star collision scientists have directly observed.
Magneto-rotational supernovas did explain the presence of europium in their model, another atom that has proved tricky to explain in the past.
But gold remains enigma.
Something out there that scientists don’t know about must be producing gold, according to Kobayashi. Or it’s possible neutron star collisions make way more gold than existing models suggest. In any case, astrophysicists have a long way to go before they can explain where all that bling came from.