Scientists: Neutron Stars Hold Gold
Updated: Thu, Apr 05 05:31 PM EDT
By CHRIS FONTAINE, Associated Press Writer
LONDON (AP) - There's gold in them thar colliding neutron stars.
A team of scientists said Thursday that the origins of most of the gold,
platinum and other heavy elements on Earth can be traced to the
massive explosions of colliding neutron stars, hundreds of millions of
years before the birth of the Solar System.
"This is an incredible result," exclaimed senior team member Stephan
Rosswog after the scientists' data were released. "It's exciting to think
that the gold in wedding rings was formed far away by colliding stars."
It has long been accepted that common elements, such as oxygen and
carbon, are created when dying stars explode into supernovae, but
researchers have been puzzled by data that suggests these stellar
explosions do not produce enough heavy elements to account for their
abundance on Earth.
The scientists - from the University of Leicester, in England, and the
University of Basel, in Switzerland - believe rare pairs of neutron stars
hold the answer.
The report was presented Thursday to the National Astronomy Meeting
at Cambridge, England.
Neutron stars are the super-dense cores of large stars that survive
supernovae. They contain about as much matter as our sun, but are
only about the size of a large city. Sometimes two are found orbiting
each other - leftovers of a binary star system. Four such pairs are
known to exist in our galaxy.
The team used a supercomputer at the U.K. Astrophysical Fluids Facility
in Leicester, 100 miles north of London, to model what might happen if
the intense gravity created by these pairs slowly forced them to spiral
closer and collide.
One such calculation takes the supercomputer several weeks to get
through, but represents just the final few milliseconds in the lives of the
two stars. It shows that as the neutron stars get closer, immense
forces tear them apart, releasing enough energy to outshine the entire
universe for a few milliseconds, the team said.
Team member Melvin Davis of Leicester said the explosion most likely
creates a black hole - a light-sucking tear in space - and ejects ash so
hot that nuclear reactions take place as it races outward, mashing
newly created protons into the nuclei of lighter elements to create
heavy elements.
The ejected material eventually mixes with the gas and dust between
stars that, in turn, collapses down to form new generations of stars,
slowly spreading heavy metals throughout the galaxy.
The proportion of matter created in these infrequent cataclysms over
the 10-billion-year life of the universe closely matches the spectrum of
elements found in our 5-billion-year-old Solar System, the team said,
providing strong evidence that the theory is solid.
"The thing that is really quite compelling is that our models really do
reproduce the relevant amounts of elements in the universe very, very
accurately," Davis said after the release of their report. "It answers
part of the question, `Where did all this stuff come from?"'
Stan Woosley, professor of astrophysics at the University of
California-Santa Cruz, called the data compelling, but said it lacked a
conclusive description of the so-called R-process - one of two ways
that heavy elements can be formed.
The other - the S-process - is better understood: Heavy elements are
created as a star burns its hydrogen into helium, but the variety and
amounts produced are limited.
Some astrophysicist believe the R-process also occurs in a supernova,
but scientists' understanding of supernovae is limited and computer
models that could prove the theory don't exist.
Supporters of the supernova theory argue that collapses of binary
neutron stars happen too infrequently. If large amounts of heavy
elements are created in the more common supernovae, it would explain
this uniformity.
"It's a nice development and a nice calculation," said Woosley, speaking
to The Associated Press by phone from California, "but not everyone is
going to accept that this is how the R-process is made."
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On the Net:
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