Australasian Science: Australia's authority on science since 1938

Oldest Stars Found Near Milky Way’s Centre

Astronomers have discovered the oldest stars ever seen, dating from before the Milky Way formed when the universe was just 300 million years old.

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

“These pristine stars are among the oldest surviving stars in the universe, and certainly the oldest stars we have ever seen,” said Louise Howes of The Australian National University. “These stars formed before the Milky Way, and the galaxy formed around them,” said Howes, who was lead author of the study published in Nature (tinyurl.com/pbcnqox).

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 said. “Perhaps they ended their lives as hypernovae – poorly understood explosions of probably rapidly rotating stars producing ten times as much energy as normal supernovae.”

ANU project leader Prof Martin Asplund said that finding such rare relic stars among the billions of stars in the Milky Way’s centre 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,” he said.

Following the team’s discovery in 2014 of an extremely old star on the edge of the Milky Way, they focused on the dense central parts of the galaxy, where stars formed even earlier. The team sifted through about five 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 and the Magellan telescope in Chile.

The team also demonstrated that the stars spend their entire lives near the Milky Way’s centre and are not just passing through it, a further indication that the stars really are the oldest known stars in the universe.