Supermassive Stars May Have Polluted the Earliest Galaxies with Nitrogen

Astronomers have uncovered a possible explanation for the unusually high nitrogen levels in some of the universe's earliest galaxies. Observations from the James Webb Space Telescope revealed that young, compact galaxies like GN-z11—located at a redshift of 10.6—contain far more nitrogen relative to oxygen than expected. Now, a team of researchers, including Sho Ebihara, Michiko S. Fujii, and Takayuki R. Saitoh, suggests that pollution from supermassive stars could be the source of this chemical anomaly.

The study focused on GN-z11, a galaxy with nitrogen-to-oxygen ratios that defy conventional models of early galactic evolution. Researchers used advanced cosmological simulations combined with detailed post-processing of supermassive star (SMS) ejecta. Their findings showed that pollution from just one of these massive stars could replicate the observed nitrogen-to-oxygen ratio in GN-z11.

The team also confirmed that the SMS pollution model matched other key abundance patterns in the galaxy, including its carbon-to-oxygen and oxygen-to-hydrogen ratios. The simulations required SMS pollution contributions of between 10 and 30 per cent to align with the telescope data.

Beyond GN-z11, the model may explain nitrogen enrichment in other distant, nitrogen-enhanced galaxies. However, the study only examined one additional high-redshift object, RX1, which was analysed for its central supermassive black hole and pulsating gas behaviour. The results suggest that supermassive stars could have played a crucial role in seeding the early universe with heavy elements.

This research offers a new way to interpret James Webb Space Telescope observations of early galaxies. By linking nitrogen enrichment to supermassive stars, the team provides a plausible mechanism for the unusual chemical signatures detected in distant systems. The findings could reshape our understanding of how heavy elements spread through the young universe.