The discovery of a star almost devoid of heavy elements provides a window to the baby years of the universe and fuels new interest in a decades-long search for the very first stars.

The star is composed almost entirely of hydrogen and helium, the raw material provided by the Big Bang. It has only traces of heavier elements.

Elements heavier than hydrogen and helium are referred to as metals by astronomers, who have known for about 50 years that nearly all metals are created in stars. Subsequent generations of stars forge heavier and heavier elements. For about three decades, researchers have been hunting for theoretical first-generation stars, which would by definition be completely metal free.

Now an international team of researchers has injected fresh enthusiasm into the whole idea with the discovery of a star they say contains just 1/200,000^th as much metal as the Sun. The finding will be reported in tomorrows issue of the journal Nature.

The star, labeled HE0107-5240, resides in a sparsely populated halo of old objects that surrounds the entire Milky Way Galaxy. Halo stars have generally been around since the galaxy formed, astronomers believe.

The star, above Southern Hemisphere skies and about 36,000 light-years away, is too dim to see without a powerful telescope. It was found in a search program carried out at the European Southern Observatory, then probed from the Siding Spring Observatory in Australia. The work was led by Norbert Christlieb of the University of Uppsala in Sweden.

"This is, in a way, the closest we have ever come to the conditions directly after the Big Bang by studying stars," Christlieb said. "But obviously, a lot must have happened between the Big Bang and the formation of this star."

Christlieb and his colleagues say such a discovery may have eluded astronomers until now simply because no one had searched so widely and for such faint stars as the new survey has. The ancient nuclear furnace is not a first generation star, however, but Christlieb said the discovery will fuel new research to find one.

The newfound star is relatively small, slightly less massive than our Sun. This, in fact, is the key to its existence and its importance to astronomers. Heres why:

Early stars were mostly huge. More massive stars tend to live shorter lives, exploding as grand supernovae. Any massive star from the early universe would have long ago cast its remains into interstellar space to be used for forging newer stars and even planets, plants and people.

It could be, however, that the newfound star once orbited a larger companion in a so-called binary configuration, says Catherine Pilachowski, an astronomer at Indiana University.

"Perhaps most, if not all, of the extremely metal-poor stars in the galaxy today originally formed as part of a binary pair, a byproduct of the formation of a massive star," said Pilachowski, who wrote an analysis of the discovery for Nature.

With just one discovery of a very low-metal star, however, Pilachowski is not ready to say exactly what the discovery will lead to and whether astronomers will get their coveted glimpse at the primordial universe.

"Only time, and the extension of new surveys to ever fainter stars, will tell," she said.

Stars are the products of the gas clouds out of which they form. So a star devoid of all metal, officially termed a Population III star, would reveal the composition of the universe in its first moments. The new finding keeps theoretical hope alive for the existence of these primordial objects.

"It implies that low-mass stars can form in extremely metal-poor environments, therefore low-mass Population III stars might have formed as well," Christlieb told SPACE.com. "If Population III stars exist, they would immediately open a window to the Big Bang."