The James Webb Space Telescope has discovered that a spiderweb protocluster is filled with tiny galaxies

Astronomers have harnessed the James Webb Space Telescope (JWST) to delve into the intricate strands of the Spiderweb protocluster, revealing unexpected discoveries in this massive cosmic structure. While the $10 billion telescope didn’t uncover a literal spider lurking in the celestial web, it did uncover new insights and previously hidden galaxies within this forming galaxy cluster, located 10 billion light-years away. Observing it at this distance means the JWST is providing a glimpse of the protocluster as it existed roughly 4 billion years after the Big Bang.

This protocluster, a nascent “cosmic city,” is home to around 100 galaxies and offers astronomers a unique opportunity to study the growth and evolution of some of the universe’s earliest large-scale structures. According to Jose M. Pérez-Martínez of the Instituto de Astrofísica de Canarias, the team is witnessing the construction of one of the universe’s largest structures, a city of galaxies in its adolescence. Over time, these galaxies will mature, shaping the properties and dynamics of this cluster, and the JWST’s capabilities are providing fresh insights into this transformative process.

Despite the Spiderweb protocluster being well-studied in the past, the JWST’s advanced infrared capabilities allowed astronomers to uncover hidden details that had remained obscured by cosmic gas and dust. While visible light is scattered and absorbed by this dense material, the telescope’s ability to capture long-wave infrared light revealed previously concealed regions of the cluster. This breakthrough enabled researchers to trace hydrogen gas in ways not achievable with ground-based instruments, unveiling galaxies within the protocluster that are typically heavily obscured.

The results, achieved with just 3.5 hours of observation, highlight the extraordinary potential of the JWST. Team member Rhythm Shimakawa of Waseda University noted that the discovery of more galaxy cluster members than anticipated was a surprise, as was the relatively low level of dust obscuring these galaxies compared to expectations. This suggests that their growth is not primarily driven by galaxy mergers or interactions but rather by gas accumulation across the large-scale structure of the protocluster. As Helmut Dannerbauer from the Instituto de Astrofísica de Canarias explained, this process fuels star formation in a more distributed manner, offering new perspectives on how these early cosmic structures evolve.