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#### Gold on Earth formed in collision of exotic stars

The gold glinting from jewelry store windows, or in your wedding band, astronomers report Wednesday,was likely born in cataclysmic mergers of an exotic, collapsed stars

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### This story is part of Dan Vergano

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# Gold on Earth formed in collision of exotic stars

Colliding stars create bling
Astronomers believe that gold, as it exists on Earth, is likely the result of cataclysmic mergers of neutron stars that occurred billions of years ago. Neutron stars, collapsed remains of imploded stars, weigh roughly 1.4 times that of our Sun. Facts about these stars:

Source: Source Harvard University; Astrophysical Journal Letters
Frank Pompa and Tory Hargro, USA TODAY
Dan Vergano @dvergano , USA TODAY 7:41 p.m. EDT July 17, 2013

## There's gold in them thar neutron stars! That's right, astronomers claim Earth's gold, the stuff of wedding bands and pricey speaker wires, originated in cataclysmic collisions of exotic stars.

Illustration of neutron star collision.(Photo: Dana Berry)

### Story Highlights

- A distant "gamma ray burst" spotted in June offers clues to where gold originates in the cosmos
- Such high-energy bursts are thought to result from the rare collision of two exotic neutron stars
- The glow left from the burst seems to confirm the production of gold occurs in the collision's aftermath

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The gold glinting on your wedding band was likely born in a cataclysmic merger of two exceedingly exotic stars, astronomers report Wednesday.

Dying stars billions of years ago cooked up most of the lighter elements in the universe, the oxygen in the air and calcium of our bones, and blasted it across the cosmos in their final explosive moments. We are stardust, as the singer Joni Mitchell put it.

But some of the heaviest atoms, including gold, defied this explanation, requiring an even more exotic origin.

A team led by Harvard astronomer Edo Berger now reports that gold is likely created as an aftereffect of the collision of two "neutron" stars. Neutron stars are themselves the collapsed remains of imploded stars, incredibly dense stellar objects that weigh at least 1.4 times as much as the sun but which are thought to be less than 10 miles wide.

While ordinary stars explode about once every century in our galaxy, Berger says, explosive collisions of two neutron stars happen only about once every 10,000 years. And it appears they spew out gold and other heavy elements in the week after their merger.

"Call it the golden glow," Berger says. "In this case, we were able to observe it for the first time and see how the merger seems to be producing (the) heavy elements."

The team bases its finding on observations of a high-energy flash of gamma rays, a "gamma ray burst" called GRB 130603B that was detected in June by NASA's Swift X-ray telescope satellite. The burst is seen as a signature of the explosive union of two neutron stars, in this case ones some 3.9 billion light-years away (one light year is about 5.9 trillion miles) the team reports in an Astrophysical Journal Letters report.

Observation of the cloudy aftereffects of the burst suggest that each merger of two neutron stars produces several moons worth of gold by weight. "At today's prices, that amount of gold would be worth 10 octillion dollars," says Berger. (That's $10,000 trillion-trillion or $10,000,000,000,000,000,000,000,000,000, for anyone counting.)

Overall about 1% of the mass of the two neutron stars was likely converted into exotic minerals by the merger, only a small part of it gold. In the collision, sub-atomic particles blasted out of the neutron stars fuse together to form heavy elements, escaping a black hole that forms afterward from the merger. Such are the likely origins for the gold that accumulated in Earth's crust some 4.54 billion years ago, swept up from space at the birth of the solar system, and now seen in jewelry store windows.

"This means (that) the Harvard team might have discovered the 'smoking gun' for unraveling the long-standing mystery which objects in the universe are responsible for the production of gold and platinum and other heavy elements," says astrophysicist Hans-Thomas Janka of Germany's Max-Planck Institute for Astrophysics."On e gets even more platinum in the same events, so even more material for mankind's jewelry!"

Janka cautioned that the gamma ray burst result represents only one observation and that astronomers will need to observe more such blasts in coming years to feel fully confident about the finding.

"It really seems that the gold in jewelry that people are wearing is the result of one of the most violent explosions in the universe: a gamma-ray burst that is produced when two neutron stars merge with each other," says astrophysicist Stephen Rosswog of Germany's Jacobs University Bremen, who first suggested the golden glow effect in 1999. "These are very difficult observations, but if this turns out to be true, this would be truly very exciting news."

The news out Wednesday says the collision of neutron stars probably generated the rare minerals such as gold that spread across the universe. An artist's depiction shows a neutron star, the crushed core of a massive star that ran out of fuel and collapsed under its own weight. NASA
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A kind of neutron star, the magnetar 1E 2259+586, shines a brilliant blue-white in this false-color X-ray image of the CTB 109 supernova remnant, which lies about 10,000 light-years away toward the constellation Cassiopeia. ESA/XMM-Newton/M. Sasaki et al.
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A neutron star is the densest object astronomers can observe directly, crushing half a million times Earth's mass into a sphere about 10 miles across, or similar in size to Manhattan Island, as shown in this illustration. NASA's Goddard Space Flight Center
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Cassiopeia A is the remains of a massive star that exploded in a supernova. Evidence for a bizarre state of matter -- a superhot, frictionless liquid -- has been found in the dense core of the neutron star left behind. The artist's illustration in the inset shows a cutout of the interior of the neutron star. Chandra X-ray Observatory Center X-ray: NASA/CXC/UNAM/Ioffe/D.Pag
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Neutron stars can pull gas off companion stars, resulting in tremendous explosions, as depicted in this NASA illustration. NASA
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An artist's illustration of two neutron stars colliding, thought to be the source of gold and other rare minerals that were spread across the universe in the resultant explosion. Dana Berry
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