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Scientists explain origins of gold

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By USA Today
Wednesday, July 17, 2013, 8:21 p.m.
 

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 effect of the collision of two “neutron” stars. Neutron stars are the collapsed remains of imploded stars, incredibly dense stellar objects that weigh at least 1.4 times as much as the sun but 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 100,000 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 based 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 about 3.9 billion light-years away, 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.) Overall about 1 percent of the mass of the two neutron stars was likely converted into exotic minerals by the merger, only a small part of it gold. 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.

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