Sydney - Australian astronomers said on Thursday they have discovered the oldest stars seen to date, formed just 300 million years after the birth of the universe.The stars lie at the heart of the Milky Way, but were formed long before the galaxy grew around them."These pristine stars are among the oldest surviving stars in the universe and certainly the oldest stars we have ever seen," said Louise Howes from the Australian National University in Canberra, lead author of the study published in the latest issue of the scientific journal Nature."These stars formed before the Milky Way, and the galaxy formed around them," Howes said on Thursday in a statement through the university."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. Perhaps they ended their lives as hypernovae - poorly understood explosions of probably rapidly rotating stars producing 10 times as much energy as normal supernovae."Project leader Professor Martin Asplund from the ANU Research School of Astronomy and Astrophysics said finding such rare relic stars among the billions of stars in the Milky Way was like finding a needle in a haystack."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 said.The team sifted through about 5 million stars observed with SkyMapper to select the most pure and therefore oldest specimens, which were then studied in more detail using the Anglo-Australian Telescope near Coonabarabran in New South Wales and the Magellan telescope in Chile to reveal their elemental make-up.The team demonstrated that the stars spend their entire lives near the Milky Way centre and are not just passing through, a further indication that the stars are the oldest known stars in the universe.