Astronomers have discovered the oldest known star, born in the fiery wake of a first generation supernova after the Big Bang.
The star, with the catchy name SMSS J031300.362670839.3, came to the attention of an international team of astronomers because of its unique chemical fingerprint showing it contained almost no iron.
The discovery is reported today in Nature.
Lead author Dr Stefan Keller says the first generation of stars that formed immediately after the big bang contained mostly hydrogen, helium and a small amount of lithium.
"They were made out of this very primordial mix of hydrogen and helium and that led them to become very massive stars, hundreds of times the mass of the Sun," says Keller, who is a research fellow at the Research School of Astronomy and Astrophysics at the Australian National University.
"When you have a star that big, it lives fast and dies young. They explode in a supernova and they start to seed the rest of the universe."
The resulting explosion contains heavier elements, such as carbon, silicon and iron.
"As soon as we've got a little bit of iron in the universe, that enables much smaller stars to form and that's what we're seeing in this finding — one of those stars from the second generation," says Kellar.
Snapshot of time
The star, which is drifting around the outskirts of the Milky Way around 6000 light years from Earth, offers a remarkable snapshot of conditions in the Universe more than 13.7 billion years ago.
"Imagine you've got a first [generation] star that's popped into existence, says it's a huge massive thing. It explodes and then the shock wave from that drives the wind out and forms the star that we're observing," he says.
"Stars act as little time capsules and when they form they encapsulate this chunk of gas from that time in which they formed. When we find a particularly old star we have this sample of the Universe as it was close to the formative phases of the Milky Way," says Keller.
That snapshot suggests the supernova that led to this star's formation was very different to supernovae seen today.
"It's completely unique in the sense that supernovae should emit large amounts of iron and various other materials. But this particular supernova evidently didn't release any iron, it released a little bit of magnesium and quite a bit of carbon," says Keller.
From this, researchers were able to deduce that this first supernova was a relatively low-energy explosion that led to the formation of a black hole.
"The primordial star's supernova explosion was of surprisingly low energy," says Keller. "Although sufficient to disintegrate the primordial star, almost all of the heavy elements such as iron, were consumed by a black hole that formed at the heart of the explosion."
This lead to the low level of iron found in the star.
The research team are now collecting data from the large telescopes in Chile to build up a more detailed picture of the star in the hope it will reveal more about the Universe's first generation of stars.
