Recent observations from the James Webb Space Telescope reveal a galaxy with sweeping, gas-filled “tentacles” in a galaxy cluster 8.5 billion light-years away, offering a rare glimpse into the early universe.
This Webb image shows the jellyfish galaxy COSMOS2020-635829; dashed circles indicate the four sources identified in the galaxy’s tail. Image Credit: Roberts et al., doi: 10.3847/1538-4357/ae3824.
Dubbed “jellyfish galaxies” for the long, trailing streams behind them, these formations are being rapidly pulled apart by the dense, hot gas within their galaxy cluster. This process, known technically as ram-pressure stripping, creates the distinctive tentacle-like structures. The discovery, made possible by Webb’s advanced capabilities, is reshaping our understanding of galactic evolution.
Researchers identified the new jellyfish galaxy, COSMOS2020-635829, while analyzing deep-space data from Webb within the well-studied COSMOS field. “We were sifting through a large amount of data from this well-studied region of the sky, hoping to uncover previously unstudied jellyfish galaxies,” explained Dr. Ian Roberts of the University of Waterloo and his colleagues. “Early in our search of the Webb data, we discovered this distant and undocumented jellyfish galaxy, which immediately sparked our interest.”
COSMOS2020-635829 exhibits a normal-looking galaxy disk with bright blue knots along its trails, indicating the presence of extremely young stars. These stars are believed to have formed outside the main galaxy within the stripped gas trails, as expected for this type of galaxy. The findings challenge previous assumptions about conditions in the early universe.
Scientists previously believed that galaxy clusters were still forming and that ram-pressure stripping was a less common phenomenon. Dr. Roberts and his team’s work suggests otherwise. “The first is that cluster environments were already harsh enough to strip galaxies, and the second is that galaxy clusters may have powerfully altered galaxy properties earlier than expected,” Dr. Roberts said. “The other is that all of the challenges mentioned may have played a role in building the large number of dead galaxies we see in galaxy clusters today.”
The team’s research yielded three additional discoveries that could alter our understanding of the universe. “This data provides us with a rare insight into how galaxies transform in the early universe,” Dr. Roberts added. The research was detailed in a paper published in The Astrophysical Journal. _____
Ian D. Roberts et al. 2026. The James Webb Space Telescope Reveals a Jellyfish Galaxy Candidate at z = 1.156. ApJ 998, 285; doi: 10.3847/1538-4357/ae3824
