Rare 2nd-Gen Star Discovered inside Ancient Relic Dwarf Galaxy | NOIRLab

Rare 2nd-Gen Star Discovered inside Ancient Relic Dwarf Galaxy | NOIRLab

This image shows the star PicII-503 with the lowest iron content ever measured outside of the Milky Way.

This image shows stars in the ultra-faint dwarf galaxy, Pictor II. Pictor II is a satellite galaxy of the Large Magellanic Cloud (LMC). LMC is a satellite galaxy of the Milky Way.

This image shows stars in the ultra-faint dwarf galaxy, Pictor II. Pictor II is a satellite galaxy of the Large Magellanic Cloud. This is a satellite galaxy of the Milky Way, and is located in the constellation Pictor. The system is made up of several thousand stars and is more than ten billion years old.

Astronomers have discovered one of the most chemically primitive stars ever identified—an ancient stellar relic that preserves the chemical imprint of the very first stars in the Universe. This star, named PicII-503, resides in the tiny, ultra-faint dwarf galaxy Pictor II. The discovery was enabled by the U.S. Department of Energy-fabricated Dark Energy Camera (DECam), mounted on the U.S. National Science Foundation Víctor M. Blanco 4-meter Telescope, at the National Science Foundation Cerro Tololo Inter-American Observatory (CTIO) in Chile, a Program of NSF NOIRLab.

Pictor II is located in the constellation Pictor. It contains several thousand stars and is more than ten billion years old. PicII-503 lies on the outskirts of the galaxy, and it contains less iron than any other star ever measured outside of the Milky Way, while also having an extreme overabundance of carbon. These signatures unmistakably match those of carbon-enhanced stars found in the outer reaches of the Milky Way, whose origins have, until now, been a mystery.

The study was led by Anirudh Chiti, Brinson Prize Fellow at Stanford University, and the results are presented in a paper appearing in Nature Astronomy.

The first stars in the Universe formed from gas that contained only the simple elements, hydrogen and helium. Within their fiery cores, this first generation of stars created the first elements heavier than helium, such as carbon and iron, that astronomers refer to as “metals.” When these stars exploded, they released their heavy elements into the interstellar medium to be recycled into the next generation of stars.

Second-generation stars are like time capsules, preserving the low amounts of heavy elements released during the explosive deaths of first-generation stars. By searching for these rare, low-metallicity stars and deriving their chemistry, scientists can better understand the mechanisms of initial element production in the Universe.

PicII-503 is the first unambiguous example of a second-generation star in an ultra-faint dwarf galaxy. It was uncovered in data from the DECam Mapping the Ancient Galaxy in CaHK (MAGIC) survey, a 54-night observing program designed to identify the oldest and most chemically primitive stars in the Milky Way and its dwarf galaxy companions. Using a specialized narrow-band filter sensitive to calcium absorption features, astronomers were able to estimate the metal content of thousands of stars from imaging data alone.

Credit: CTIO/NOIRLab/DOE/NSF/AURA

Image Processing: T.A. Rector (University of Alaska Anchorage/NSF NOIRLab), M. Zamani & D. de Martin (NSF NOIRLab)

Acknowledgments: PI: Anirudh Chiti, Alex Drlica-Wagner

Date: March 16, 2026

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