Los Angeles: Gold is rare on Earth in part because its also rare in the universe. Unlike elements like carbon or iron, it cannot be created within a star. Instead, it must be born in a more cataclysmic event--like one that occurred last month known as a short gamma-ray burst (GRB).
Observations of this GRB provide evidence that it resulted from the collision of two neutron stars -- the dead cores of stars that previously exploded as supernovae. Moreover, a unique glow that persisted for days at the GRB location potentially signifies the creation of substantial amounts of heavy elements -- including gold.
"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!" says lead author Edo Berger of the Harvard-Smithsonian Center for Astrophysics (CfA).
A gamma-ray burst is a flash of high-energy light (gamma rays) from an extremely energetic explosion. Most are found in the distant universe. Berger and his colleagues studied GRB 130603B which, at a distance of 3.9 billion light-years from Earth, is one of the nearest bursts seen to date.
Gamma-ray bursts come in two varieties -- long and short -- depending on how long the flash of gamma rays lasts. GRB 130603B, detected by NASAs Swift satellite on June 3rd, lasted for less than two-tenths of a second.
Although the gamma rays disappeared quickly, GRB 130603B also displayed a slowly fading glow dominated by infrared light. Its brightness and behavior did not match a typical "afterglow," which is created when a high-speed jet of particles slams into the surrounding environment.
Instead, the glow behaved like it came from exotic radioactive elements. The neutron-rich material ejected by colliding neutron stars can generate such elements, which then undergo radioactive decay, emitting a glow thats dominated by infrared light --exactly what the team observed.
"We have been looking for a "smoking gun" to link a short gamma-ray burst with a neutron star collision. The radioactive glow from GRB 130603B may be that smoking gun," explains Wen-fai Fong, a graduate student at the CfA and a co-author of the paper.
The team calculates that about one-hundredth of a solar mass of material was ejected by the gamma-ray burst, some of which was gold. 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, 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," says Berger.
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