The most pristine star yet found in the known universe was discovered in the Magellanic Cloud

From the first moments after the Big Bang, the universe was a dense, hot mixture of energetic particles composed almost exclusively of hydrogen and helium. Over time, that material expanded, cooled, and began to coalesce into neutral gas. The densest patches surrendered to their own gravity and collapsed inward, giving rise to the first generation of stars—forged from those two primordial elements alone.

Those pioneer stars burned intensely and died young, but not before manufacturing heavier elements in their cores and scattering them across the cosmos through supernova explosions. From that stellar debris, subsequent generations were born, each carrying a more chemically complex fingerprint than the last. In astronomy, all elements heavier than hydrogen and helium are collectively referred to as «metals,» and their abundance in a star is a direct indicator of when and where it formed. The less metal a star contains, the more ancient and chemically pristine it is.

An unusual team of astronomers has now used data from the Sloan Digital Sky Survey’s fifth generation (SDSS-V) and observations conducted at the Magellan telescopes at Carnegie Science’s Las Campanas Observatory in Chile to discover what is currently the most pristine star in the known universe: SDSS J0715-7334. Their findings have been published in Nature Astronomy.

Hunting for the universe’s earliest stars

The research was led by Alexander Ji, an astrophysicist at the University of Chicago and former Carnegie Observatories postdoctoral fellow, alongside Carnegie astrophysicist Juna Kollmeier, who leads SDSS-V. The team identified SDSS J0715-7334 as a second-generation star—one that formed just a few billion years after the universe began, inheriting only a minimal chemical inheritance from the very first stellar generation.

The Big Bang produced a universe made almost entirely of hydrogen and helium. Over hundreds of millions of years, gravity drew the densest pockets of this gas inward until the first stars ignited. These objects burned fast and ended violently, seeding space with newly forged elements. The stars that followed were built from this enriched material. Finding a star with almost none of those heavier elements means finding one that formed extraordinarily early, before the cosmos had time to accumulate much chemical complexity.

«These pristine stars are windows into the dawn of stars and galaxies in the universe,» Ji explained. Several of his co-authors on the paper are undergraduate students from the University of Chicago, whom Ji brought to Las Campanas on an observing trip during spring break. For many of them, the experience proved transformative—and the discovery itself happened during their very first Magellan observing run, in the early hours of the morning.

Why rare stars matter to science

Astronomers interested in the universe’s earliest stellar generations cannot observe those first objects directly—they are too distant and too ancient. Instead, they search for their surviving descendants in our cosmic neighborhood: second- and third-generation stars that still preserve, in their chemical composition, a record of what came before.

«We have to look in our cosmic backyard to find these objects, because we can’t yet observe individual stars at the dawn of star formation. Since these stars are rare, surveys like SDSS-V are designed to have the statistical power to find these needles in the stellar haystack and test our theories of star formation and explosion,» explained Kollmeier.

SDSS-V, now in its fifth generation, is one of the most ambitious spectroscopic surveys ever undertaken. It takes millions of optical and infrared spectra across the entire sky, deploying both the du Pont telescope at Las Campanas in the Southern Hemisphere and the Apache Point Observatory in New Mexico in the Northern Hemisphere. The sheer volume of data it generates allowed Ji and his students to identify stars with very few heavy elements—and then follow up with the Magellan telescopes for high-resolution confirmation.

A record broken by a wide margin

Deeper analysis of the Magellan spectra revealed something extraordinary: SDSS J0715-7334 contains less than 0.005% of the metal content found in the Sun. It is twice as metal-poor as the previous record holder for most pristine star, with particularly low abundances of iron and carbon. More strikingly, it is 40 times more metal-poor than the most iron-poor star previously known—a margin that places it in an entirely different category of chemical purity.

Additional data from the European Space Agency’s Gaia mission allowed the team to establish that SDSS J0715-7334 lies approximately 80,000 light-years from Earth and was not born within the Milky Way. It originated elsewhere—most likely in the Large Magellanic Cloud—and was pulled into our galaxy over cosmic time, making it an ancient immigrant whose journey has only now come to light.

A powerful telescope partnership in Chile

The discovery could not have happened without the complementary strengths of Las Campanas Observatory’s instrument suite. SDSS-V’s du Pont telescope provided the initial survey data that flagged SDSS J0715-7334 as a candidate of exceptional interest. The Magellan telescopes then delivered the high-resolution spectra that confirmed just how chemically pristine the star truly is.

«The ecosystem of telescopes at Las Campanas was critical to nearly every aspect of this breakthrough work,» said Michael Blanton, Director and Crawford H. Greenewalt Chair of the Carnegie Science Observatories. The project also stands as a demonstration of how survey astronomy and targeted follow-up observations can work in concert to produce discoveries that neither approach could achieve alone.

For Ji, the experience carried a personal dimension as well. His own postdoctoral training at Carnegie shaped his scientific career, and bringing undergraduate students to the same observatory—where they contributed directly to a record-breaking discovery—was a way of paying that experience forward. After the star’s identification was confirmed, Ji restructured the remainder of the semester so that students could dedicate their time to analyzing what they had found.

«Training the next generation of astronomers is critical to the future of our field. And building excitement about the practice of science by undertaking projects like this is a great way to ensure that curious-minded young learners can see themselves in astrophysics,» Ji concluded.

The challenge ahead is to find more stars like SDSS J0715-7334—objects that can serve as direct witnesses to the chemical state of the universe in its earliest chapters, and that can test theoretical models of how the very first stellar generation lived and died.

Alexander P. Ji et al., A nearly pristine star from the Large Magellanic Cloud, Nature Astronomy, 2026. DOI: 10.1038/s41550-026-02816-7

© 2026 SKYCR.ORG | Homer Dávila Gutiérrez, FRAS. All rights reserved. Reproduction in whole or in part without express authorization is prohibited. Original source: Carnegie Institution for Science / Nature Astronomy (2026).