An article published in the journal “Monthly Notices of the Royal Astronomical Society” reports the discovery of a primordial galaxy that was cataloged as GS-NDG-9422, or simply 9422, in which nebular gas outshines stars. A team of researchers used observations conducted with the James Webb Space Telescope to study 9422 using in particular the NIRSpec (Near-Infrared Spectrograph) instrument to analyze its chemical composition. The conclusion is that this galaxy is in a phase never seen before in its evolution in which very massive and very hot stars make the nebular gas very hot and consequently bright.
The image (NASA, ESA, CSA, STScI, A. Cameron (University of Oxford)) shows the area of the sky where the galaxy GS-NDG-9422, or simply 9422, was spotted, magnified in the inset in a view captured by the James Webb Space Telescope’s Near Infrared Camera (NIRCam).
According to star formation models, the first stars in the history of the universe may have been colossal, with surface temperatures reaching 80,000° Celsius. The most massive stars known today have surface temperatures of 40,000-50,000° Celsius. To hit nebular gas to the point of making it glow in infrared light like that detected in galaxy 9422, the models developed by the authors of this study suggest that primordial supermassive stars are needed.
Observations conducted with the James Webb Space Telescope during the JWST Advanced Deep Extragalactic Survey (JADES) show the galaxy 9422 as it was about a billion years after the Big Bang. This means that it’s a primordial galaxy but not old enough to have some of the first stars in the universe, which could have had a very short life in astronomical terms and extremely intense. According to the researchers who studied 9422, it could be in a phase in which there’s a significant formation of very massive stars still capable of making the surrounding gas bright.
The discovery of the galaxy 9422 still leaves questions unanswered. It’s not clear whether it’s a rare case or a common phase in the evolution of primordial galaxies. Its stars contain elements heavier than hydrogen and helium not present in the first stars in the universe but their characteristics could help us better understand the early stages of the life of galaxies.
The James Webb Space Telescope’s extraordinary performance is allowing astronomers to probe the early universe in ways that were unthinkable before its launch. Finding other early galaxies in a phase like 9422 remains difficult because they’re dim even for Webb, but surveys already conducted such as JADES to explore the early universe and the ones underway or scheduled for the future will provide a lot of new information that could be crucial in reconstructing the history of the first stars and the galaxies that hosted them.
