It was formed a couple of hundred million years after the Big Bang that brought the universe into being, they believe.
Previous contenders for the title of oldest star are around 13.2bn years old — two objects described by European and US teams respectively in 2007 and 2013.
Stefan Keller of the Australian National University in Canberra said the Methuselah star is — in cosmic terms — relatively close to us.
It lies in our own galaxy, the Milky Way, at a distance of around 6,000 light years from Earth. The star catalogues list it by the number of SMSS J031300.36-670839.3.
“The tell-tale sign that the star is so ancient is the complete absence of any detectable level of iron in the spectrum of light emerging from the star,” Keller said.
The Big Bang gave rise to a universe filled with hydrogen, helium, and a trace of lithium, he explained.
All the other elements that we see today were forged in stars, which are born in clouds of gas and dust bequeathed by supernovae — huge stars that explode at the end of their life.
The star was discovered using the university’s SkyMapper telescope, which is carrying out a five-year survey of the southern sky.