Discover PicII-503: A Protostar in the Ancient Pictor II Dwarf Galaxy

“This marks the first definitive detection of element formation in protogalaxies,” stated Dr. Aniru Chitty, a postdoctoral researcher at the University of Chicago, now at Stanford University.

“This discovery fills a crucial gap in understanding the origin of elements during the universe’s formative years.”

In the primordial epochs following the Big Bang, the cosmos was relatively simple, comprised almost entirely of hydrogen, helium, and lithium, giving rise to giant stars primarily formed by these elements.

More complex elements, like calcium and gold, were scarce since they had to be synthesized within stars themselves.

At the cores of these massive stars, nuclear fusion processes created increasingly heavier elements.

When these stars eventually exploded, they contributed to the formation of new stars, perpetuating this cycle until a diverse array of elements emerged, forming the universe we know today.

“To track elemental formation, we must search for stars with minimal heavy elements, as these accumulate over time,” explained University of Chicago astronomer Alexander Gee.

Using the Magellan Telescope at Las Campanas Observatory and ESO’s Very Large Telescope, astronomers identified a significant candidate star within the ultrafaint dwarf galaxy Pictor II.

This star, identified as PicIII-503, exhibits a remarkable structure, with an iron content approximately 1/100,000 times lower than that of our Sun.

This extraordinary finding not only generates excitement but also offers insights into the enigmatic origins of these early stars.

Consequently, since PicIII-503 remains within its original protogalaxy, astronomers have uncovered vital information regarding its formation theory, particularly related to the star’s explosive death.

“Upon the demise of a massive star, it possesses an ‘onion-skin’ structure: lighter elements like carbon reside in outer layers while heavier elements are found inside,” Gee noted.

“A weak explosion may only eject the outer layers, allowing the heavier inner materials to coalesce with neighboring gas and dust, which can form future generations of stars.”

“However, a vigorous explosion could propel these materials far beyond the small galaxies that existed during that era,” he added.

This exciting discovery provides context for the abundance of carbon-rich stars observed in our Milky Way, illuminating their origin, Dr. Chitty emphasized.

For more on the discovery of PicIII-503, refer to the research paper published in Nature Astronomy.

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A. Chitty et al. Enrichment by the first stars of relic dwarf galaxies. Nat Astron published online on March 16, 2026. doi: 10.1038/s41550-026-02802-z