Many common elements, such as oxygen and carbon, are known to be made
in stars and distributed through the Universe when a star explodes as a
supernova. This is the origin of most of the material that makes up the
Earth.

It is becoming clear, however, that normal stars cannot make enough of the
heavy elements, such as gold and platinum. Thus the origin of gold and
platinum — on Earth and throughout the Universe — remains a mystery.

Dr Stephan Rosswog and co-workers from the Universities of Leicester and
Basel, Switzerland, will be reporting to the UK National Astronomy Meeting
on Thursday 5 April about a new way to make gold, platinum and other heavy
elements.

COLLIDING NEUTRON STARS AND PRECIOUS METALS

Rosswog’s team has explored the idea that these heavy elements were formed
in the violent collisions of super-dense neutron stars. These stars — the
dead cores of old stars — weigh a million times more than the Earth but
are only the size of London.

Neutron stars are sometimes found close together in pairs and Dr. Rosswog
has calculated what happens when these binary stars are close enough to
collide. In addition to a huge amount of energy released — enough to fuel
the most powerful explosions in the Universe (known by astronomers as
gamma-ray bursts) — he has found that a large quantity of gold and
platinum is made and thrown out into space.

Dr Rosswog’s calculations were made on a new supercomputer at the UK
Astrophysical Fluids Facility (UKAFF) based in Leicester. The UKAFF
computer is one of the first Origin 3800 supercomputers made by Silicon
Graphics Inc. It is special because it has 128 processors that can work
together in parallel on a single problem.

Together with 64GB of RAM and 1300GB of disk space, this is the most
powerful computer in Europe dedicated to astronomical calculations.
It began operation in October 2000, making Dr Rosswog’s calculations
possible for the first time.

The calculations are difficult because they include a lot of exotic physics,
including the effects of quantum mechanics and Einstein’s general theory of
relativity. Dr. Rosswog builds two model neutron stars in the UKAFF computer,
and starts his calculation with them close enough for Einstein’s theory to
force them to spiral together.

A single calculation takes weeks on the supercomputer, representing just the
final few milliseconds in the life of the two stars. As they spiral closer,
immense forces tear them apart, releasing huge amounts of energy — enough
to outshine the entire Universe for a few milliseconds. The stars collapse
to form a black hole, but Dr. Rosswog’s calculations show that some of their
material is thrown out into space (images of the simulation are available
on the UKAFF web site — see below).

This explosive ash is still extremely dense and hot, around a billion
degrees Celsius, allowing the necessary nuclear reactions to take place.
Relatively small seed nuclei, made of elements like iron, collect neutrons
and build themselves up to become heavy elements such as gold and platinum.

The ash, now containing gold and platinum, gradually cools down and
continues to fly out into deep space. It mixes with the gas and dust
between stars that eventually, in turn, collapse down to form new
generations of stars.

Dr. Rosswog and his colleagues have shown that the relative amounts of
elements formed in his models of colliding neutron stars match those seen
in our Solar System. This provides strong evidence that most of the gold
and platinum on Earth was formed in the violent collisions of distant stars.

Dr. Rosswog says, “This is an incredible result. It’s exciting to think that
the gold in wedding rings was formed far away by colliding stars.”

Professor Andrew King (Director of UKAFF at University of Leicester) says,
“This fascinating result shows that the new UKAFF supercomputer is keeping
the UK at the forefront of world astronomy.”

BACKGROUND INFORMATION

The United Kingdom Astrophysical Fluids Facility (UKAFF) is a 5.9 million
pound project funded jointly by the government and the computer company
Silicon Graphics, with further support from the Particle Physics and
Astronomy Research Council and the Leverhulme Trust.

The facility was formally opened by Dr John Taylor, Director General of the
UK Research Councils, on October 31st, 2000.

CONTACT

Dr. Stephan Rosswog

Department of Physics and Astronomy

University of Leicester

University Road

Leicester

LE1 7RH

Phone: +44 (0)116-223-1219

E-mail: sro@star.le.ac.uk

(Dr Rosswog will be in Basel 25 March – 1 April, Tel. no. +41 61-267-3785)

Prof. Andrew King (same address as above)

Phone: +44 (0)116-252-2072

E-mail: ark@star.le.ac.uk

FOR VIDEOS AND IMAGES SEE:

* UKAFF web page

http://www.ukaff.ac.uk/movies/nsmerger