Astronomers have discovered that galaxies were already being shaped by their surroundings just 1.2 billion years after the Big Bang, much earlier than scientists once believed.
Using the powerful James Webb Space Telescope along with observations from the Subaru Telescope, researchers studied a huge ancient structure called the Loktak Protocluster, located about 12.6 billion light-years from Earth.
The findings, published in The Astrophysical Journal Letters, suggest that where a galaxy “lives” has influenced how it grows since the very early history of the universe.
Today, galaxies are not spread evenly through space. Many belong to enormous galaxy clusters containing hundreds or even thousands of galaxies. These giant structures formed gradually over billions of years as gravity pulled matter together.
In the early universe, the first versions of these clusters were still under construction. Scientists call these young structures “protoclusters.” They are essentially the seeds of today’s massive galaxy clusters.
One of the biggest questions in astronomy has been when these crowded environments first started affecting galaxy growth.
In the modern universe, galaxies inside clusters often look very different from isolated galaxies. Cluster galaxies are usually larger, rounder, and slower at forming new stars. Astronomers refer to this as an “environmental effect,” meaning a galaxy’s surroundings influence how it evolves.
Until now, researchers were unsure whether these effects already existed in the young universe.
To investigate, an international team led by researchers from the National Astronomical Observatory of Japan searched the early universe using the Subaru Telescope’s Hyper Suprime-Cam. They focused on galaxies that emit a special type of light called Lyman-alpha emission, which is produced when energetic young stars excite hydrogen gas.
These galaxies act like bright markers that help astronomers map large cosmic structures.
The team discovered a huge concentration of galaxies linked together in one giant system. They named it the Loktak Protocluster after Loktak Lake in India, famous for its floating islands, because the galaxy groups appear connected in a similar way.
Researchers then used the James Webb Space Telescope to compare galaxies inside the protocluster with galaxies living in less crowded regions at the same time in cosmic history.
When viewed in ultraviolet light, which highlights areas of active star formation, the galaxies looked fairly similar. But when scientists examined them in optical light, which reveals the overall distribution of stars, a major difference appeared.
Galaxies inside the protocluster were about 1.4 times larger than galaxies in ordinary environments.
This suggests that although star formation in galaxy centers was happening at similar rates, galaxies in crowded regions were building up their outer structures more quickly.
The discovery shows that environmental effects were already influencing galaxy evolution extremely early in cosmic history. Even when the universe was still very young, a galaxy’s future depended not only on its own properties, but also on the cosmic neighborhood where it formed.
Future observations with new instruments on the Subaru Telescope and additional JWST studies may reveal whether this early environmental influence was common across the universe or something unique to the Loktak Protocluster.
