Astronomers using the James Webb Space Telescope (JWST) have discovered a spectacular “cosmic jellyfish” galaxy, designated COSMOS2020-635829, that existed 8.5 billion years ago. This distant galaxy, observed as it appeared just 5.3 billion years after the Big Bang, offers a rare glimpse into a crucial period of galactic development and may reshape our understanding of how galaxies evolved in the early universe.
The Anatomy of a Cosmic Jellyfish
COSMOS2020-635829 is a jellyfish galaxy – named for the long, trailing tendrils of gas that resemble a jellyfish’s tentacles. These trails form as the galaxy moves through dense clusters, encountering strong winds that strip away its gas in a process called “ram-stripping.” The JWST’s high-resolution imaging reveals bright blue knots within these tendrils, indicating regions where new stars are actively forming.
Why this matters: Jellyfish galaxies are relatively rare and provide a unique laboratory for studying how galactic environments impact evolution. By observing them at such an early stage of the universe, astronomers can test theories about how galaxy clusters shaped the structure we see today.
Discovery in the COSMOS Field
The team identified COSMOS2020-635829 while analyzing JWST data from the COSMOS field, a region of the sky known for its clarity and abundance of distant galaxies. This area is ideal because it is far from the Milky Way’s bright center, minimizing obstructions.
Team member Ian Roberts noted that the discovery was made while sifting through a large dataset. The unusual morphology of this galaxy immediately caught their attention.
Unexpected Findings Challenge Existing Models
The JWST image of COSMOS2020-635829 shows a galactic disk that is structurally similar to modern galaxies. The presence of young stars forming within the gas trails, however, presents a surprise.
Previously, scientists believed that galaxy clusters 8.5 billion years ago wouldn’t have been dense enough to cause significant ram-stripping. The discovery suggests that these environments were harsher than anticipated, and that galaxy clusters may have begun altering galactic properties much earlier in cosmic history.
This has critical implications: The process of ram-stripping could have played a key role in the formation of the large population of “dead” galaxies (galaxies no longer actively forming stars) observed in modern galaxy clusters.
Future Research
The team plans to continue studying COSMOS2020-635829 to unravel further mysteries about jellyfish galaxies and their role in galactic evolution. The JWST’s capabilities will be essential for refining our understanding of how early universe environments shaped the galaxies we see today.
The team’s findings were published on February 17 in The Astrophysical Journal. The featured image was captured by the Hubble Space Telescope.
