The first stars were massive, hot, and bright, forming from primordial clumps of hydrogen and helium. They lived fast and died young, but not before producing new elements in their stellar remains that would later birth generations of stars. Scientists know this much, but many questions still remain about those ancient stars.
A group of astronomers has found the most chemically pristine star yet, potentially making it the oldest known star in the cosmos. The star may have formed in the first several billion years after the Big Bang, a celestial relic that’s part of the second generation of objects in the universe.
The discovery, published in Nature Astronomy, offers a rare glimpse into the evolution of ancient stars and how they transitioned to the smaller, longer-lasting ones commonly found today. “These pristine stars are windows into the dawn of stars and galaxies in the universe,” Alexander Ji, assistant professor of astronomy and astrophysics at the University of Chicago and lead author of the new study, said in a statement.
A star is born
In the beginning, the universe was a hot, murky, and dense soup of particles that cooled down and expanded over time. Scientists believe the first stars began to form only a few hundred million years after the big bang, approximately 13.7 billion years ago.
The first generation of stars formed from pristine hydrogen and helium. Within their cores, however, atoms would fuse into heavier elements. When those first stars burnt their fuel and exploded, a new generation was forged from their remains. As this process repeated, each generation of stars possessed more heavy elements.
“All of the heavier elements in the universe, which astronomers call metals, were produced by stellar processes—from fusion reactions occurring within stars to supernovae explosions to collisions between very dense stars,” said Ji.
The first generation of stars is faint and has not yet been directly observed. Astronomers hoping to gather clues on the early evolution of stars search for ones that are metal-poor, meaning they have low amounts of heavy elements like iron and carbon.
The team behind the recent discovery set out to look for ancient stars, scouring through catalogs made by the Sloan Digital Sky Survey in search of anomalous readings. In April 2025, the team journeyed to the Magellan Telescopes at Carnegie Science’s Las Campanas Observatory in Chile to get a closer look at a short list of candidate stars.
One particular star stood out for having less than 0.005% of the Sun’s metal content. “The more we looked at it, the more it looked like it was real,” Natalie Orrantia, an undergraduate astronomy student at the University of Chicago and co-author of the study, said in a statement.
Ancient times
The star, named SDSS J0715−7334, is located around 80,000 light-years away from Earth. Further analysis of the star’s composition confirmed it as the new record holder for stellar purity, making it the most chemically pristine star ever observed.
In fact, SDSS J0715-7334 is twice as metal-poor as the previous record-holder (J1029+1729). The exceptionally pristine star has particularly low amounts of iron and carbon.
Using data from the European Space Agency’s Gaia mission, the team behind the discovery was able to identify the star as a galactic immigrant. The star may have formed elsewhere in the cosmos and later got pulled into the Milky Way galaxy.
The discovery also helps scientists better understand how stars grew smaller over time, and it may be due to the absence of cosmic dust during the universe’s infancy. “That dust is everywhere in the universe now, but we weren’t sure whether dust would have existed back then,” Pierre Thibodeaux, a graduate student at the University of Chicago and co-author on the study, said in a statement. “If there was dust present, that could cause the gas to fragment into clumps, and then you get several smaller stars instead of one big one.”
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