Gold on Earth Came from Colliding Stars, Astrophysicists Say

Jul 18, 2013 by Sci-News.com

According to new research by Dr Edo Berger and his colleagues at the Harvard-Smithsonian Center for Astrophysics, all Earth’s gold likely came from colliding neutron stars.

Optical afterglow of GRB 130603B (A. Cucchiara et al / Gemini South team)

Optical afterglow of GRB 130603B (A. Cucchiara et al / Gemini South team)

Unlike elements like carbon or iron, gold cannot be created within a star. Instead, it must be born in more cataclysmic events known as gamma-ray bursts (GRBs).

Dr Berger’s team studied the gamma-ray burst GRB 130603B, detected by NASA’s Swift satellite on June 3, 2013. At a distance of 3.9 billion light-years from Earth, the event is one of the nearest bursts seen to date.

GRB 130603B observations provide evidence that it resulted from the collision of two neutron stars. Moreover, a unique glow that persisted for days at the GRB location potentially signifies the creation of substantial amounts of heavy elements, including gold.

Gamma-ray bursts come in two varieties – long and short – depending on how long the flash of gamma rays lasts. GRB 130603B 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 didn’t match a typical ‘afterglow,’ which is created when a high-speed jet of particles slams into the surrounding environment.

Instead, the GRB 130603B’s 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 that’s dominated by infrared light – 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. The radioactive glow from GRB 130603B may be that smoking gun,” said Dr Wen-fai Fong, co-author of a paper submitted for publication in the Astrophysical Journal Letters (preprint at arXiv.org).

The scientists have calculated that about one-hundredth of a solar mass of material was ejected by the gamma-ray burst, some of which was gold.

This artist's conception portrays two neutron stars at the moment of collision. Such collisions produce rare heavy elements, including gold (Dana Berry / SkyWorks Digital, Inc.)

This artist’s conception portrays two neutron stars at the moment of collision. Such collisions produce rare heavy elements, including gold (Dana Berry / SkyWorks Digital, Inc.)

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,” Dr Berger concluded.

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Bibliographic information: E. Berger et al. 2013. Smoking Gun or Smoldering Embers? A Possible r-process Kilonova Associated with the Short-Hard GRB 130603B. ApJ L, submitted for publication; arXiv: 1306.3960