Astronomers Discover a Rare Primitive Star That Provides a Chemical Snapshot of the Early Universe

PicII-503 is likely a second-generation star, born from the remnants of the very first stars, according to a new study

Kunjal Bastola | Editorial Intern

March 30, 2026

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Astronomers have discovered one of the most chemically primitive stars at the edge of our Milky Way galaxy. The star, called PicII-503, seems to be a member of the universe’s second generation of stellar objects, born from the exploded leftovers of the very first stars, researchers report March 16 in the journal Nature Astronomy.  

“It’s a fantastic discovery,” Anna Frebel, an MIT astrophysicist who was not involved in the study, tells Jay Bennett at Science News. “I know how hard it is to find these stars. They are so, so rare.”

The primitive star was first spotted in 2024 with the Víctor M. Blanco Telescope in Chile. It’s in an ultrafaint dwarf galaxy called Pictor II, which is more than ten billion years old and approximately 150,000 light-years from Earth. The small, ancient galaxy sits in the bubble, or “halo,” of old stars that surrounds the Milky Way, which may have formed from relic dwarf galaxies merging with our larger one.

Follow-up observations of PicII-503 with additional telescopes revealed a specific chemical signature: The star contains low abundances of iron and calcium and a relatively high amount of carbon.

The composition hints that the star holds traces of heavy elements from the very first stars during their explosive deaths. These early stars probably lived for just a few million years and were mostly made of the lightest elements, hydrogen and helium. However, under intense heat and pressure in the stars’ cores, the substances fused into heavier elements, such as carbon and iron, which astronomers consider to be “metals.”

One hypothesis posits that when the first stars died in low-energy supernovas, the heaviest, innermost of the newly made elements, such as iron, probably fell back onto the stellar corpses. But the lighter, more exterior ones, like carbon, were spewed into space and seeded the second generation of stars.

PicII-503 supports this idea because it was found in one of the smallest known dwarf galaxies. If the supernova that produced PicII-503 had been high-energy, the elements that spurred the star would have been blown away from Pictor II’s precursor, and maybe even ripped it apart.

“What excites me the most is that we have observed an outcome of the very initial element production in a primordial galaxy, which is a fundamental observation,” says lead author Anirudh Chiti, an astrophysicist at Stanford University, in a statement. PicII-503’s chemical fingerprint also resembles those observed in other low-metal stars in the Milky Way’s halo, he adds, hinting that they also came from the remnants of the first stars.

Astronomers have found roughly ten stars in this region as primitive as PicII-503, reports Science News. But the recent discovery is the first unambiguous second-generation star found in an ultrafaint dwarf galaxy, which “validates” the hypothesis that this type of star was born from the initial ones, Frebel tells the outlet.

What’s more, PicII-503 contains so little calcium and iron that the researchers suspect that it was seeded by a single supernova, which means it might be one of the earliest second-generation stars.

“Discoveries like this are cosmic archaeology, uncovering rare stellar fossils that preserve the fingerprints of the universe’s first stars,” says Chris Davis, the National Science Foundation program director for NOIRLab, which supported the research, in the statement.

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Kunjal Bastola is an editorial intern with Smithsonian magazine.