'Oldest' star found in galaxy

HE0107-5240 lies in the outer reaches of our galaxy

By Dr David Whitehouse BBC News Online science editor

This is the oldest star in our Milky Way yet observed by astronomers. It could date back to the beginning of the Universe, about 14 billion years ago.

The giant star, HE0107-5240, is a rarity because unlike younger stars it is virtually metal-free. It is from the first generation of stars made from the simple elements left over from the Big Bang.

Writing in the journal Nature researchers say, "these old stars provide crucial clues to the star formation history and the synthesis of chemical elements in the early Universe.

They add: "If totally metal-free stars could be found, this would allow the direct study of the pristine gas from the Big Bang."

First generation

After the Big Bang, the Universe consisted of mostly hydrogen, some helium and a little lithium, so the first stars to form would have contained only these elements.

It was the first generation of stars that converted these lighter elements into heavier ones like carbon, phosphorous, iron and lead - collectively known to astronomers as metals.

When those stars exploded they "polluted" the cosmos with these heavier elements, which themselves went into a later generation of stars - like our Sun.

The existence of stars with zero or very low metal content has been predicted for decades, but none has ever been found, leading some to suspect they never existed - until the discovery of HE0107-5240.

Large telescope

The star was spotted in the outer reaches of our galaxy by Norbert Christlieb, at the University of Hamburg in Germany, and colleagues.

It lies in the direction of the southern constellation Phoenix, at a distance of about 36,000 light-years.

The star has just 1/200,000th of the metal content of our Sun.

It was initially discovered at the Siding Spring Observatory in Australia. High precision follow-on observations were made at the European Southern Observatory in Chile, using one of the huge, new units of the Very Large Telescope (VLT).

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The discovery of HE0107-5240 fills an important gap in theories about how elements form in star, but it also raises some questions.

Why have no stars been found between 1/10,000 and 1/200,000 of the Sun's metal abundance?

"Only time, and the extension of new surveys to even fainter stars will tell," says Catherine Pilachowski, an astronomer at Indiana University in Bloomington, US.