They might not look like much, but these blurry flickers of light - right there in the middle - are the oldest stars ever to be observed by the human eye.

Discovered by a team of astronomers at the Australian National University (ANU), these ancient stars were born when our Universe was a youthful 300 million years old.

"These pristine stars are among the oldest surviving stars in the Universe, and certainly the oldest stars we have ever seen," said Louise Howes, lead author of the study published in the latest issue of Nature.

Howes says the stars are older than the Milky Way itself. Our galaxy formed later, around the stars.

"We've found what we think are are the oldest stars in the galaxy and potentially the oldest objects ever discovered," Howes adds.

Howes and her team are confident that the stars are so old because of their composition and location. They contain very little "metal" – a term astronomers use to define any element other than hydrogen and helium. These metals are released into space when stars explode in supernovae. They then become incorporated into new stars that form later.

If stars are unusually metal-poor it is probably because they formed very early in the history of the Universe, before many stars had exploded and scattered metals through space.

But there's an alternative. Even today, it's possible that there are metal-poor regions of space that could give birth to stars that are metal-poor despite being very young.

The researchers looked at the way their stars move to confirm that some of them have always lived in what is now the dense, metal-rich centre of the Milky Way. If this is where the stars were born, the only way to account for their low metal content is if they predate the formation of the Milky Way.

"The stars have surprisingly low levels of carbon, iron and other heavy elements, which suggests the first stars might not have exploded as normal supernovae," say Howes.

These discoveries challenge current theories about the environment of the early Universe.

"Calculating the age of a star is not easy," adds Howes.

Using ANU's SkyMapper telescope, the team observed about 5 million stars. From the initial 5 million, 14,000 stars were examined individually. The 23 most interesting stars became the subject of the paper.

"The Milky Way is so massive and we're only such a small part of it," says Howes. "What I hope to be able to do in the future is to work out exactly how the Milky Way formed and these stars are the very first building blocks of that."

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