Astronomers have discovered stars forming in the dwarf galaxy Sextans A that defy conventional understanding of star formation. These stars are “cooking” without essential elements like silicon, carbon, and iron—the building blocks typically required for stellar birth—raising questions about how the early universe operated and how cosmic dust is created.
The Anomaly in Sextans A
Sextans A, a small galaxy near the Milky Way, has a strikingly low “metallicity,” meaning it contains only 3% to 7% of the heavier elements found in our sun. This is because its relatively small size prevents it from retaining these heavier materials, which are forged in dying stars and spread through supernovas. Traditionally, low metallicity environments were thought to be inhospitable to significant dust production, a critical step in star formation.
However, observations from the James Webb Space Telescope (JWST) reveal otherwise. Instead of being dust-free, as expected, stars in Sextans A are actively creating dust grains composed almost entirely of iron—a phenomenon never before observed in similar stellar environments.
“Every discovery in Sextans A reminds us that the early universe was more inventive than we imagined,” says Martha Boyer, lead author and astronomer at the Space Telescope Science Institute.
Unexpected Chemistry
The JWST’s Mid-Infrared Instrument has focused on Asymptotic Giant Branch (AGB) stars in Sextans A – stars nearing the end of their lives. In metal-rich galaxies, these stars typically produce silicate dust. But in Sextans A, the lack of metals forces them to rely on an entirely different “recipe,” forging dust from iron instead.
Furthermore, the team also detected pockets of polycyclic aromatic hydrocarbons (PAHs), carbon-based molecules that are expected to thrive in metal-rich galaxies. Models predicted their absence in a metal-poor environment like Sextans A. Yet, they persist in small, dense gas clumps, suggesting that PAHs can survive even in the harshest cosmic conditions if shielded from the broader environment.
Implications for Early Universe Studies
These discoveries matter because they challenge existing models of star formation and the chemical evolution of galaxies. The early universe was likely filled with environments like Sextans A – small, metal-poor galaxies where stars formed under extreme conditions. If stars could create dust and sustain complex molecules without abundant metals, our understanding of early star formation needs revision.
The findings suggest that cosmic dust may have formed through previously unknown mechanisms, potentially challenging the long-held assumption that supernovas were the primary source of this essential material. Astronomers will continue observing Sextans A with JWST to refine their understanding, but the current results indicate that the universe’s early kitchens were far more resourceful than previously imagined.
