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. Credit: Dana Berry, SkyWorks Digital, Inc. High Resolution Image (jpg) - Low Resolution Image (jpg) - More images
This animation shows the collision and merger of two neutron stars.
Merging neutron stars can create an event known as a short gamma-ray
burst.Credit: Dana Berry, SkyWorks Digital, Inc. Low Resolution Image (jpg) - Animation (mov)
Cambridge, MA - We
value gold for many reasons: its beauty, its usefulness as jewelry, and
its rarity. Gold is rare on Earth in part because it's 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).
Berger presented the finding today in a press conference at the CfA in Cambridge, Mass.
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 NASA's
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 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. Berger's co-authors are Wen-fai Fong and Ryan Chornock, both of the CfA.
Headquartered in Cambridge, Mass., the
Harvard-Smithsonian Center for Astrophysics (CfA) is a joint
collaboration between the Smithsonian Astrophysical Observatory and the
Harvard College Observatory. CfA scientists, organized into six research
divisions, study the origin, evolution and ultimate fate of the
universe.
David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu
Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu
