Australian Scientists Discovered the Oldest Star on the Books

Scientists based out of the Australian National University have discovered the oldest star on the books. The discovery sheds new light—pun intended—on the composition of the earliest batches of stars cooked up in the infancy of the universe. “This is the first time that we’ve been able to unambiguously say that we’ve found the chemical fingerprint of a first star,” said Dr. Stefan Keller, lead researcher on the study, in an ANU press release.

Named SMSS J031300.36-670839.3 (and hereafter called J-etc), this stellar old-timer has been knocking about for about 13.6 billion years, making it barely younger than the universe itself. Indeed, it is a second-generation sun, born from the fallout of the very first supernovae. And as an extra bonus, J-etc is local: it's only 6,000 light years away from Earth, and is a Milky Way native. Home team pride.

The method for finding this needle in a galactic haystack is truly ingenious. For the last five years, the Skymapper Telescope, based out of Siding Spring Observatory near Coonabarabran, has been sweeping the skies looking for stars that essentially have a case of stellar anemia. In other words, Skymapper flags stars with spectral signatures that show very low iron content.

The spectral band of the senior star. Photo via. Twitter/Anna Frebel.

The more iron-deficient the star, the older it is likely to be. This is because the universe's very first suns didn't have access to the abundance of heavy elements that today's whippersnapper stars mine. Iron, cobalt, manganese, and other elements formed from supernova nucleosynthesis have cumulatively increased with each supernova cycle, meaning the older the star, the lower its iron content.

J-etc is by far the most anemic star ever discovered, with about 10 million times less iron than our sun. As Keller explained: “To make a star like our sun, you take the basic ingredients of hydrogen and helium from the Big Bang and add an enormous amount of iron – the equivalent of about 1,000 times the Earth’s mass. To make this ancient star, you need no more than an Australia-sized asteroid of iron and lots of carbon. It’s a very different recipe that tells us a lot about the nature of the first stars and how they died.”

The discovery has already led to some unexpected revelations about the behavior of early stars. It was, for example, assumed that first-gen supernovae ejected a large amount of iron to be used by the following generation. But the fact that J-etc is mostly polluted with carbon and magnesium flies in the face of that theory. It “indicates the primordial star’s supernova explosion was of surprisingly low energy. 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,” said Keller.

It would appear that the oldest star ever discovered has lots of stories to tell.