TURNING STARS INTO GOLD
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."
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.
Dr. Stephan Rosswog Department of Physics and Astronomy University of Leicester University Road Leicester LE1 7RH
(Dr Rosswog will be in Basel 25 March - 1 April, Tel. no. +41 61-267-3785)
Issued by: RAS Press Officers Peter Bond
Dr Jacqueline Mitton