A supercomputer has produced a simulation of what the first stars to form in the Universe must have been like.

The stars would have ignited in the clouds of hydrogen, helium and the mysterious "dark matter" formed after the Big Bang.

The new three-dimensional model of the dynamics in these clouds shows objects forming from very small fluctuations. As the objects assemble, the hydrogen cools and sinks to form dense, cold, gas clouds. At the centre of these clouds, stars are formed.

The work, reported in the journal Science, indicates that the very first star resulted from the gravitational collapse of a cloud of hydrogen and helium about 100 times more massive than our Sun.

First light

"Our modelling suggests that the first star may have condensed from a protogalactic cloud into a self-gravitating, fully molecular mass of hydrogen and helium at least 100 times that of our Sun," said Michael Norman, professor of physics at the University of California, US.

"We think that such objects may have become the first stars to shine in the Universe."

One important consequence of star formation is the production of progressively heavier chemical elements.

Atoms heavier than lithium that occur naturally throughout Universe are the result of nucleosynthesis, the process by which stars "forge" more massive elements from lighter ones.

Scientists believe that it took many generations of stars - each processing the debris left by earlier ones and then redistributing it through stellar explosions, or supernovae - to produce the present elemental abundances found in the Universe.

The big picture

"Thus, the first heavy elements had to be not only synthesised, but also released and distributed within the first billion or so years after the Big Bang," said Norman. Only supernovae of sufficiently short-lived massive stars could provide such an enrichment mechanism, he said.

While astronomers agree that the first generation of cosmic structures formed massive stars, there has been no general agreement on the nature of the first large-scale structures.

Globular clusters, super-massive black holes and Jupiter-size bodies all have been proposed. Yet the evolution of the large-scale structure of the Universe depends very much on the details of the very first structures to form.

What was the first star like? "The picture we get from our simulations suggests that all metal-free stars are very massive and form in isolation," Norman said.