Dead colliding stars brought gold to earth
 Source : Agencies, News Bharati English  Date : 19-Jul-2013

Neutron Stars Collision

Massachusetts, July 19 : All the gold on Earth must have come from colliding dead stars, scientists have suggested after studying a gamma ray burst (GRB) that happened when two neutron stars collided on June 3 rdthis year.

It was known that gold must have cosmic origins like many of the heavier elements. But gold is so heavy that it could not be created even in stars, like iron. It needed a cataclysmic event for gold to be forged.

Scientists at the Harvard-Smithsonian Center for Astronomy (CfA) observing the gamma ray burst last month found that a unique glow that persisted for days at the GRB location potentially signifies the creation of substantial amounts of heavy elements - including gold. The gamma ray burst was a death scream of two neutron stars colliding and merging, some 3.9 billion light years away.

Neutron stars are super-dense stars made of just neutrons. They are born after a star explodes in a supernova. A neutron star is said to have a density like a Boeing 747 compressed to the size of a grain of sand.

"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 CfA in a statement.

Although the gamma rays disappeared in just one-fifth of a second, a slowly fading glow dominated by infrared light persisted for some more time. 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 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," 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.

The team's results have been submitted for publication in The Astrophysical Journal Letters and are available online.