Astronomers using data from NASA’s James Webb Space Telescope have identified dozens of small galaxies that played a starring role in transforming the early universe into the one we know today. The study, led by Isak Wold, analyzed images captured by Webb’s NIRCam and NIRSpec instruments to discover these tiny but mighty galaxies.
The research suggests that these small galaxies were responsible for producing ultraviolet light that drove the cosmic renovation, which occurred when the universe was about 800 million years old. According to Wold, “These small galaxies punch well above their weight” in terms of producing ultraviolet light.
The team mapped a giant galaxy cluster known as Abell 2744, which is located about 4 billion light-years away. The study found 83 small starburst galaxies at this age, which was 6% of the universe’s current age of 13.8 billion years.
To detect these galaxies, Wold and his colleagues used a novel sample selection technique combined with gravitational lensing. They found that if the low-mass starburst galaxies release a similar amount of ultraviolet light as present-day green peas, they could account for all of the ultraviolet light needed to convert the universe’s neutral hydrogen to its ionized form.
The discovery provides new insights into the history of the universe and sheds light on which types of objects were most responsible for reionization. With this study, NASA’s Webb Telescope has addressed one of its main goals: understanding key questions about the major transition in the universe’s history.
Source: https://phys.org/news/2025-06-webb-uncovers-galaxy-population-cosmic.html