The James Webb Space Telescope (JWST) offers astronomers a unique opportunity to explore distant galaxies that exist far beyond the early Universe. Some of these galaxies exhibit chemical signatures that may suggest the presence of exotic supermassive stars, possibly weighing up to 10,000 times that of our Sun.

These enormous stars are puzzling, as our current understanding suggests that stars in the nearby universe generally have a maximum size limit. “Our models for galaxy evolution are predicated on the assumption that stars cannot exceed around 120 solar masses,” explains Devesh Nandal at the Harvard-Smithsonian Center for Astrophysics, Massachusetts. “While we had theorized about stars potentially larger than this, there were no observational data to validate it.”

That all changed recently. Nandal and his team analyzed JWST observations of a distant galaxy dubbed GS 3073, discovering its chemical signature contained an unexpectedly high concentration of nitrogen. Though elevated nitrogen levels have also been noted in several other remote galaxies,

For most galaxies, nitrogen concentrations aren’t high enough to cause ambiguity and can be attributed to certain classes of relatively ordinary stars or other cosmic phenomena. However, this isn’t the case for GS 3073, as Nandal asserts that the nitrogen levels are simply too elevated.

There exists a hypothetical category of protostar referred to as a Population III star, which models indicate can grow to considerable sizes. Simulations suggest that if these stars form, they would produce significantly more nitrogen than typical stars. Nandal and his co-researchers concluded that only a handful of Population III stars—ranging from 1,000 to 10,000 solar masses—could account for the excess nitrogen observed in GS 3073. “Our research provides the most compelling evidence yet for the existence of Population III supermassive stars in the early universe,” he declares.

However, some scholars challenge whether only supermassive Population III stars can account for this data, or if they do so accurately. “Population III should be linked with an environment where elements heavier than helium are scarce,” notes Roberto Maiorino of Cambridge University. “Conversely, GS 3073 is a fairly chemically mature galaxy, which makes it seem ill-suited for the types of environments typically associated with Population III.”

On the other hand, John Regan from Maynooth University in Ireland suggests that this may simply be an unusual galaxy. “When we look back at the early universe, what we see are incredibly strange, exotic galaxies. It’s challenging to assert that we shouldn’t expect the formation of supermassive stars simply because it’s peculiar; you just claimed these galaxies are quite bizarre,” he states.

If these colossal stars truly exist, they may unlock mysteries related to the formation of supermassive black holes in the universe’s distant past. Should they originate from supermassive stars instead of conventional stars, we could gain critical insights into how these black holes achieved their immense sizes in what appears to be a relatively brief time frame.

Confirming the existence of supermassive stars in GS 3073 and other nitrogen-rich galaxies from the early Universe is complex, and additional discoveries of these chemical signatures may be necessary. “It’s quite challenging to bolster the argument for their existence; establishing definitive signatures is difficult,” Regan lamented. “Nonetheless, this indication is incredibly robust.”