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

An illustration shows the collision of two neutron stars. Scientists had proposed that such collisions might have filled our solar system with gold, but new research casts doubt on that claim.
An illustration shows the collision of two neutron stars. Scientists had proposed that such collisions might have filled our solar system with gold, but new research casts doubt on that claim.
(Image: © NASA/Swift/Dana Berry)

Something is raining gold across the universe. But 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's an intense nuclear fusion reaction. But such intense fusion doesn't happen frequently enough, at least not nearby, to make the giant trove of gold we find on  Earth and elsewhere in the solar system. And a new study has found the most commonly-theorized origin of gold — collisions between neutron stars — can't explain gold's abundance either. So where's the gold coming from? There are some other possibilities, including supernovas so intense they turn a star inside out. Unfortunately, even such strange phenomena can't explain how blinged out the local universe is, the new study finds.

Related: The 12 strangest objects in the universe

Neutron star collisions build gold by briefly smashing protons and neutrons together into atomic nuclei, then spewing those newly-bound heavy nuclei across 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. And, in a regular supernova, that gold gets sucked into the black hole. 

So what about those odder, star-flipping supernovas? This type of star explosion, a so-called magneto-rotational supernova, is "a very rare supernova, spinning very fast," Kobayashi told Live Science.

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. As it dies, the star shoots white-hot jets of matter into space. And because the star has been turned inside out, its jets are chock full of gold nuclei. Stars that fuse gold at all are rare. Stars that fuse gold then spew it into space like this are even rarer.

But even neutron stars plus magneto-rotational supernovas together can't explain Earth's bonanza of gold, Kobayashi and her colleagues found.

"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. But those studies didn't account for the rarity of those collisions. It's hard to precisely estimate how often tiny neutron stars — themselves the ultra-dense remnants of ancient supernovas — slam together. But it's certainly not very common: Scientists have seen it happen only 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.

 

"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. But those studies didn't account for the rarity of those collisions. It's hard to precisely estimate how often tiny neutron stars — themselves the ultra-dense remnants of ancient supernovas — slam together. But it's certainly not very common: Scientists have seen it happen only 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.

Related: 15 amazing images of stars

"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.

But Kobayashi and her colleagues' new paper, published Sept. 15 in The Astrophysical Journal, has one big advantage: It's extremely thorough, Roederer said. 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.

Pulling all that data together in a useful way, he said, amounts to a "Herculean effort."

Using this approach, 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 (92 protons and 146 neutrons). That's an impressive range, Roederer said, covering elements that are usually ignored in these types of studies.

Mostly, the math worked out.

Neutron star collisions, for example, produced strontium in their model. That matches observations of strontium in space after 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 an enigma.

Something out there that scientists don't know about must be making gold, Kobayashi said. Or it's possible neutron star collisions make way more gold than existing models suggest. In either case, astrophysicists still have a lot of work to do before they can explain where all that fancy bling came from.

Originally published on Live Science.

  • MikePerry
    There's actually an easy explanation for our abundance of gold, one that's part of the privileged planet thesis. It says that we see on Earth and in our Solar System is atypical of the galaxy as a whole. Gold is as rare elsewhere as the science predicts. But in another of many lucky accidents, a source of gold seeded our Solar System with an abundance of it. There's nothing unusual about that. On Earth itself, gold is unevenly distributed. The same could be true of our galaxy.
    Reply
  • TorbjornLarsson
    MikePerry said:
    There's actually an easy explanation for our abundance of gold,

    The article was on work detailing the abundance in the universe, as well as explanations for it - the work shows the explanations are complex.

    Despite that complexity many element abundances are explained, some are not and some like gold are IIRC (I browsed the paper days ago) nearly so - the work in progress is promising.

    "Something is raining gold across the universe." I don't know why they mentioned gold or in part of the article refer to recent work looking specifically on element isotope abundances in our own system to study local sources but at a guess it makes the article more click-worthy. I don't think there is an unusual amount of gold in our system or that it was discussed in the work, but maybe I have missed that - but as you say, some sources are local (and recent) so our mileage may vary on the average abundance. C.f. how our solar system was believed to be uncommonly metal rich, but with better statistics it lies just at the edge of the median peak so nothing but random outcome on most elements.

    Uneven distribution of crust elements is curious though. Seems to me the claim among geologists is that generic sorting is thermal due to magma melts (I may have gotten that wrong, I read that in passing the other day and haven't checked it yet). But there are also biosphere mechanisms that for instance laid down banded iron formations and pyrite ("fool's gold").

    By your prompting me to search, I see that gold is a bit complex in that regard. Gold belongs with rare earth elements to the element group that mostly sank to the core during Earth accretion, so the current abundance is due to later impacts.

    And gold sorts in many ways: "On Earth, gold is found in ores in rock formed from the Precambrian time onward. It most often occurs as a native metal, typically in a metal solid solution with silver (i.e. as a gold silver alloy). Such alloys usually have a silver content of 8–10%. Electrum is elemental gold with more than 20% silver. Electrum's color runs from golden-silvery to silvery, dependent upon the silver content. The more silver, the lower the specific gravity. Native gold occurs as very small to microscopic particles embedded in rock, often together with quartz or sulfide minerals such as "fool's gold", which is a pyrite. These are called lode deposits. The metal in a native state is also found in the form of free flakes, grains or larger nuggets that have been eroded from rocks and end up in alluvial deposits called placer deposits. Such free gold is always richer at the surface of gold-bearing veins owing to the oxidation of accompanying minerals followed by weathering, and washing of the dust into streams and rivers, where it collects and can be welded by water action to form nuggets." https://en.wikipedia.org/wiki/Gold#Occurrence ]
    Reply
  • Botaggart
    Sounds like an unknown answer needs a new solution. We know of super massive black holes and super novas. Why would it be unreasonable that a black hole reaches a gravitational saturation and explodes. That would explain lots of things including gold.
    Reply
  • Angelo
    Or perhaps our distant ancestors could make Gold? There is information in the ancient Vedic scriptures of gold being produced from the mixture of mercury and bellmetal ( I don't have the recipe) as well as being produced from other sources unbeknownst to us.
    Reply
  • TorbjornLarsson
    Botaggart said:
    Sounds like an unknown answer needs a new solution. We know of super massive black holes and super novas. Why would it be unreasonable that a black hole reaches a gravitational saturation and explodes. That would explain lots of things including gold.

    As I commented earlier, the work is complex but promising so far.

    But of course they are looking for new sources as solution. Black holes would not be among them since they cannot explode, their main characteristic is precisely that they are so compact that the integrated surface gravity is too strong for any escape. ) Black holes can eventually shrink and disappear through the quantum effect of Hawking radiation.)

    By the way, today black hole discovery and theory work scientists were awarded this year's Nobel Prize in Physics (prompted by the recent black hole shadow image no doubt)!
    Reply
  • TorbjornLarsson
    Angelo said:

    Or perhaps our distant ancestors could make Gold? There is information in the ancient Vedic scriptures

    Alchemistry and religion is erroneous superstition twice over.
    Reply