A team of astronomers from Carnegie University and the University of Chicago combined data from the fifth phase of the Sloan Digital Sky Survey and observations from the Magellan Telescope in Chile to successfully locate the most primitive star known to date - SDSS J0715-7334. Relevant results were published in the new issue of the journal Nature Astronomy.
Red giant SDSS J0715-7334 artwork. This star was born near the Large Magellanic Cloud and has now "settled" in the Milky Way. Image source: Carnegie University
Academic circles generally believe that the first generation of stars came into being about hundreds of millions of years after the Big Bang. These first-generation stars quenched heavy elements in violent nuclear fusion, and the second-generation stars that were subsequently born were nurtured in these debris rich in new elements. The astronomical community collectively refers to all elements in the universe that are heavier than helium as "metals." Therefore, the proportion of heavy elements in a star (i.e. metallicity) becomes a natural yardstick for inferring the age of its birth. Stars with extremely low metal content are called "primitive stars" or "metal-poor stars."
SDSS J0715-7334 belongs to the second generation star lineage and is a red giant. Spectral and chemical analysis by the Magellan Telescope showed that its metal content is less than 0.005% of the sun, and its total metallicity is as low as about 7.8×10-7, which is only half of the previous record holder and 1/40 of the poorest iron-poor star known, breaking the observation record to date. SDSS J0715-7334 not only has an extremely low iron content, but is also extremely deficient in carbon. It is different from similar stars that are usually "poor in iron and rich in carbon".
Using data from the European Space Agency's Gaia spacecraft, the team traced the star's trajectory. It was originally born near the Large Magellanic Cloud and now "resides" in the Milky Way, about 80,000 light-years away from Earth.
Such primitive stars are like a window through time and space, allowing people to glimpse the dawn of the universe's galaxies and stars. They not only provide key clues for revealing the evolution of early stars, but will also become a natural laboratory for testing the origin of stars and the Big Bang theory.