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Gold and Other Elements Formed in Rare Collision of Neutron Stars: A Study

Jul 18, 2013 03:03 PM EDT
Neutron Star Collision
This artist's conception portrays two neutron stars at the moment of collision. New observations confirm that colliding neutron stars produce short gamma-ray bursts. Such collisions produce rare heavy elements, including gold. All Earth's gold likely came from colliding neutron stars.
(Photo : Dana Berry, SkyWorks Digital, Inc.)

There's a good reason gold is pricey - the kind of explosions needed to create it only happen once every 10,000 years, a new study published in The Astrophysical Journal Letters argues.

As rare in the universe as it is on Earth, gold cannot be created within a star, unlike elements such as carbon or iron. For this reason, its origins have long remained a mystery to science with some pointing to solutions such as supernovae for answers.

Now, through the study of a recent gamma-ray burst (GRB) that appears to have resulted from the collision of two neutron stars, a team of researchers believe they may have finally solved the puzzle.

Neutron stars is the term given to the tiny, incredibly dense cores left after a star explodes. They, too, can explode when both stars in a binary star system detonate, leaving their burned out cores to circle each other until their gravity pulls them so close they collide.

This process, which occurs approximately 100 times less frequently than the explosion of an ordinary star, is where all elements heavier than iron are born, according to the study.

Supporting this theory was a unique glow that persisted for days in the region of the GRB that the scientists believe may signify the creation of a substantial amount of these elements.

"We estimate that the amount of gold produced and ejected during the merger of the two neutron stars may be as large as 10 moon masses - quite a lot of bling!" lead author Edo Berger of the Harvard-Smithsonian Center for Astrophysics (CfA) said in a press release.

The glow, they explained, didn't behave like typical "afterglow" created when a high-speed jet of particles slams into the surrounding environment. Rather, it acted as though it came from exotic radioactive elements. Neutron-rich material ejected by colliding neutron stars can generate such elements, which then undergo radioactive decay. When this happens, the glow is dominated by infrared light, which is exactly what the team observed.

"We've been looking for a 'smoking gun' to link a short gamma-ray burst with a neutron star collision," said Wen-fai Fong, a graduate student at the CfA and a co-author of the paper, adding that the recently observed glow from the GRB just might be "that smoking gun."

In all, the team calculates that approximately one-hundredth of a solar mass of material was ejected by the explosion that took place 3.9 billion lightyears away and caused the recent GRB.

Some of that, they believe, is gold.

Sure enough, by combining the estimated gold produced by a single short GRB with the number of such explosions that have occurred over the age of the universe, the researchers determined that all the gold in the cosmos might have come from gamma-ray bursts.

"To paraphrase Carl Sagan, we are all star stuff, and our jewelry is colliding-star stuff," Berger said.

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