The nine stars, found near the centre of the Milky Way, are surprisingly pure but contain material from an even earlier star, which died in an enormous explosion called hypernova, the researchers noted.

"These pristine stars are among the oldest surviving stars in the Universe, and certainly the oldest stars we have ever seen," said , lead author of the study Louise Howes from The Australian National University (ANU).

"These stars formed before the Milky Way, and the galaxy formed around them," Howes explained. The discovery and analysis of the nine pure stars challenges current theories about the environment of the early universe from which these stars formed.

"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," Howes noted. "Perhaps they ended their lives as hypernova - poorly understood explosions of probably rapidly rotating stars producing 10 times as much energy as normal supernovae,"  Howes said.

Finding such rare relic stars amongst the billions of stars in the Milky Way centre was like finding a needle in a haystack, project leader professor Martin Asplund, from ANU explained.

"The ANU SkyMapper telescope has a unique ability to detect the distinct colours of anaemic stars - stars with little iron - which has been vital for this search," Asplund pointed out.

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