Bold claim, startling as this sounds: James Webb has uncovered a cosmic jellyfish that shouldn’t exist this early in the universe. In the deep-field observations of the Cosmic Evolution Survey (COSMOS) Deep field, a distant galaxy shows dramatic gas tails that look like oceanic tentacles, a signature researchers tie to strong environmental forces inside galaxy clusters. This discovery could sharpen our understanding of how galaxies evolve during what scientists often call the universe’s adolescence.
The subject is a class of galaxies affectionately nicknamed jellyfish galaxies, named for their trailing streams of gas that resemble sea jellyfish’s dangling limbs. In this case, the gas tendrils emanate from a disk that otherwise resembles a typical spiral galaxy, producing an image that is both striking and scientifically informative.
A Distinct Jellyfish in the COSMOS Field
Astronomers identified COSMOS2020-635829 while combing through the JWST data gathered from the COSMOS field, a region chosen for its distance from the Milky Way’s plane and its relative absence of bright foreground clutter. Space.com notes that this clarity makes COSMOS particularly suitable for studying distant, ancient galaxies.
“We were sifting through a large dataset from this well-studied sky patch with the goal of finding jellyfish galaxies that had not yet been documented,” said Ian Roberts of the Waterloo Centre for Astrophysics. “Early in our JWST data search, we found a distant, previously undocumented jellyfish galaxy that immediately grabbed our attention.”
The galaxy appears as it existed about 5.3 billion years after the Big Bang. At that epoch, galaxy clusters were still coalescing, placing the observed processes in a particularly intriguing context.
Ram-Pressure Stripping and Star Formation in the Tails
Jellyfish galaxies earn their name from the long gas tails that trail behind them. These features arise through a mechanism called ram-pressure stripping: as galaxies move through the dense environments of clusters, the intracluster medium exerts a strong wind that can push gas out of the galactic disk.
In the JWST image, the galaxy’s disk looks relatively normal, similar to present-day spirals, aside from its distinct gaseous tails. Within those tails, bright blue knots mark clusters of newly formed stars. Their youth shows that these stars originated outside the main disk, forming directly in the stripped gas. Similar structures have been observed before, including by the Hubble Space Telescope, but detecting them at this distance and at this stage of cosmic history adds a new layer to the story.
A Surprising Twist for the Early Universe
Perhaps the most surprising aspect is the timing. Prior expectations suggested that 8.5 billion years ago, cluster environments would not have generated enough pressure to trigger widespread ram-pressure stripping.
The new observation challenges that view. Roberts notes two key implications: first, cluster environments were already harsh enough to strip galaxies; second, galaxy clusters may have altered galaxy properties earlier than previously thought. These processes might have contributed to the large population of “dead” or quiescent galaxies seen in clusters today. He adds that this data provides rare insight into how galaxies were transformed in the early universe.
The research team plans to continue examining COSMOS2020-635829 with the James Webb Space Telescope to unravel more about jellyfish galaxies and the forces that shaped them billions of years ago, potentially rewriting parts of our timeline for galactic evolution.
