Relic star poses cosmic puzzles

Primitive stars are depleted in "heavy" elements such as iron

Astronomers have identified what could be one of the earliest stars formed in the Universe, Nature magazine reports.

Scientists think the cosmic relic may consist largely of elements created in the hot gas that existed just 15 minutes after the Big Bang.

The star has a very low iron content - an elemental signature that suggests it is made of fresh material that was never processed by an earlier star.

But other such signatures are unusual for a very primitive stellar object.

It's remarkable but apparently what we see in these stars is the tiny amount of lithium produced in the Big Bang Timothy Beers, Michigan State University

The new star HE1327-2326 and another star called HE0107-5240 have the lowest abundances of heavy elements known.

About 13.7 billion years ago, the Universe consisted of a hot gas with a temperature high enough to produce the lightest chemical elements.

The rapid expansion after the first 15 minutes of the Universe put an end to the synthesis of new elements by the process of nucleosynthesis.

However, after about 200 million years, the Universe grew large enough for haloes of dark matter to form and this triggered the formation of the first stars.

Unexpected elements

These first stars synthesised all the heavier elements, from carbon to uranium, that form the basis of solid planets and organic life.

Over the past 25 years, astronomers have been scouring the skies for stars with a composition that reflects these first stellar objects.

The new star HE1327-2326 has an unexpectedly low abundance of the metal lithium and an unexpectedly high amount of the metal strontium for such a primitive star.

"The lithium problem is immediately more troublesome. Many of the primitive stars studied in the past have lithium abundances that are very similar to one another," said co-author Timothy Beers, of Michigan State University in East Lansing, US.

"It's remarkable but apparently what we see in these stars is the tiny amount of lithium produced in the Big Bang."

"Yet in this star, it's not at that perfect value, so we're a bit confused as to why that might be."

Further research on this star and others like it may help shed light on where the lithium in primitive stars came from.

"When we get such extreme objects as this it really forces the people who model how these elemental abundances come about to take a close look at what they might be missing," Professor Beers told BBC News.

One possibility is HE1327-2326 is a binary system. If the primitive star's binary companion had the opportunity to evolve, it might start to synthesise heavier metals including strontium.

The evolving binary might then cast off its outer envelope, allowing some of the material to be accepted by its primitive companion, explaining the high strontium content.

The research was an international collaboration involving researchers from Australia, Japan, Germany, Sweden and the US.