At 13.6 billion years old, a star spotted by Australian astronomers is the oldest yet found, they say. It's about 6,000 light years away from our planet—which is fairly close, the Wall Street Journal reports, and it's in our Milky Way galaxy. How do the astronomers know it's so old? It's "the complete absence of any detectable level of iron in the spectrum of light emerging from the star," writes Stefan Keller, one of the researchers. Iron quantity, he writes at the Conversation, is "a qualitative 'clock' telling us when the star was formed."
The star appears to be a second-generation star, created following the explosion of an earlier one. "The shock wave from those first stars gave rise to this star that we are observing now," Keller says. "It unambiguously incorporates material from the first stellar generation." And it's giving experts a window into earlier stars: "By studying the light from this star in detail we have, for the first time, seen the chemical fingerprint of the first stars to form in the universe," Keller writes. (Click to read about another incredible discovery, this one on Earth.)