Astronomers have discovered an exceptionally ancient star that provides a rare window into the early universe.

An international team identified the most chemically pristine star ever observed, SDSS J0715-7334, using data from the Sloan Digital Sky Survey-V (SDSS-V) and follow-up observations with the Magellan telescopes at Carnegie Science’s Las Campanas Observatory in Chile. The findings are published in Nature Astronomy.

Figure 1. Ancient Star Journey: SDSS J0915-7334 from the Large Magellanic Cloud to the Milky Way

The study was led by University of Chicago astronomer Alexander Ji, a former Carnegie Observatories postdoctoral fellow, with contributions from Carnegie astrophysicist Juna Kollmeier, who directs SDSS-V. Analysis indicates that this star belongs to the second generation of stars, forming a few billion years after the Big Bang.

“These pristine stars offer a glimpse into the earliest stars and galaxies in the universe,” Ji said. Several of his co-authors, undergraduate students from the University of Chicago, joined him and Kollmeier on a spring break observing trip to Las Campanas Observatory last year. “My first visit to LCO sparked my passion for astronomy, and it was meaningful to share that formative experience with my students,” he added.

Tracing the Universe from the Big Bang to the First Stars

After the Big Bang, the universe existed as an extremely hot and dense mix of particles. As it expanded and cooled, neutral hydrogen gas formed. Over hundreds of millions of years, slightly denser regions collapsed under gravity, leading to the formation of the first stars, made almost entirely of hydrogen and helium. These early stars burned brightly but lived short lives. Before dying, they produced heavier elements through nuclear fusion and dispersed them into space via powerful explosions. Subsequent generations of stars formed from this enriched material, gradually increasing the diversity of elements across the universe.

The Importance of Metal-Poor Stars

“All heavier elements in the universe, known as metals by astronomers, are produced through stellar processes—from fusion inside stars to supernovae and collisions between dense stars,” said Ji. “Finding a star with extremely low metal content signaled to these students that they had discovered something extraordinary.”

Researchers like Ji and Kollmeier focus on second- and third-generation stars because they retain clues about the evolution of star formation across cosmic history. Since the earliest stars cannot yet be observed directly, astronomers search for ancient survivors closer to the Milky Way.

“These stars are rare, so surveys like SDSS-V are designed to have the statistical power to locate these ‘needles in the stellar haystack’ and test our theories of star formation and explosions,” Kollmeier explained.

The Sloan Digital Sky Survey is one of the most influential astronomical projects ever undertaken. Its current phase, SDSS-V, collects millions of optical and infrared spectra using telescopes in both hemispheres, including the du Pont telescope in Chile and the Apache Point Observatory in New Mexico. Using this data, Ji and his students identified stars with extremely low heavy-element content and confirmed their findings through high-resolution spectra from the Magellan telescopes. During their first observing run, SDSS J0715-7334 was verified as the most chemically pristine star known.

“The telescope network at Las Campanas was essential to this breakthrough, from the du Pont data mapping the Milky Way to the Magellan observations that revealed just how unique SDSS J0715-7334 truly is,” said Michael Blanton, Director of the Carnegie Science Observatories.

An Engaging Collaborative Learning Experience

Las Campanas Observatory, home to four Carnegie telescopes, played a central role in this project, which primarily utilized two of its instruments—highlighting how modern technology continues to push the boundaries of scientific discovery.

Students experienced this collaborative environment firsthand: on their first night, they observed SDSS-V data collection at the du Pont telescope, and the next night, they conducted their own observations with the Magellan Clay telescope.

Following the discovery, Ji adapted the semester schedule to allow students to focus on analyzing their results, giving them practical insight into how flexibility can accelerate scientific progress.

Kollmeier reflected on the experience: “As an undergraduate, I preferred research over classes. I’m thrilled that Alex’s course became a hands-on curriculum of discovery, and I hope surveys like SDSS-V and Gaia help make such experiences the norm rather than the exception.”

The Unique Nature of This Star

A detailed analysis revealed that SDSS J0715-7334 contains less than 0.005% of the Sun’s metal content, making it half as rich in heavy elements as the previous record holder. Its iron and carbon levels are particularly low, and it is 40 times more metal-poor than the most iron-deficient star previously discovered.

By combining these findings with data from the European Space Agency’s Gaia mission, the team determined that the star lies roughly 80,000 light-years from Earth and likely formed outside the Milky Way before being captured by our galaxy.

Ji emphasized the importance of hands-on learning for aspiring astronomers: “Training the next generation is vital for the future of our field [1]. Projects like this spark curiosity and allow young learners to envision themselves in astrophysics. My postdoctoral experience at Carnegie was pivotal to my growth, and I’m thrilled to pass that forward by bringing my students to Las Campanas.”

Reference:

1. https://scitechdaily.com/astronomers-discover-the-most-pristine-star-ever-found/

Cite this article:

Janani R (2026), Astronomers Identify the Most Pristine Star on Record, AnaTechMaz, pp.821