Conventional wisdom holds that the first stars were born of the hydrogen and helium present in the early universe. They themselves then began forging 'metals' (elements heavier than helium) such as carbon, phosphorous and lead. When these first-generation stars eventually reached the end of their life cycle, they exploded as supernovae, scattering their metallic contents across the universe, so the story goes. But despite decades of searching for stars to verify that scenario, researchers had only turned up representatives containing too much metal to be relevant.
The new star, however, "is the closest astronomers have come to having direct knowledge of the elemental composition of the universe shortly after the Big Bang," study co-author Timothy C. Beers of Michigan State University remarks. Unlike previously found stars, which contained around 1/10,000 of the metal in our Sun, the newly discovered star has just 1/200,000 of our Sun's metal. "This is perhaps the first identification of a true second-generation star," Beers remarks. Its low metal content, he adds, "is evidence of the previous generation of massive stars that exploded as supernovae."
Still mysterious, however, is why scientists haven't found any intermediately metal-rich stars. To that end, Indiana University astronomer Catherine A. Pilachowski writes in a commentary accompanying the Nature report, "Only time, and the extension of new surveys to even fainter stars, will tell."