Using the James Webb Space Telescope (JWST), astronomers have captured a stunning image of a "cosmic jellyfish." This aquatic-creature-like galaxy, designated COSMOS2020-635829, was seen as it existed 8.5 billion years ago, or around 5.3 billion years after the Big Bang. Astronomers say it could paint a more detailed picture of the evolution of galaxies at a crucial period in the adolescent universe.
COSMOS2020-635829 is an example of a jellyfish galaxy, a class of galaxies that get their moniker from the fact that they possess trailing tendrils of gas that resemble the flexible, stinging appendages of their oceanic namesakes. For jellyfish galaxies, these trails are created as they 'swim' through their galaxy cluster homes against the flow of strong winds that push on them, forcing out gas, a process called "ram-stripping."
The team discovered COSMOS2020-635829 while examining data collected by the JWST from a patch of sky over Earth called the Cosmic Evolution Survey Deep field, or the COSMOS field. This region is favored by astronomers for the study of distant and ancient galaxies because it lies away from the plane of the Milky Way and is clear of bright objects that would serve as obstructions.
"We were looking through a large amount of data from this well-studied region in the sky with the hopes of spotting jellyfish galaxies that haven’t been studied before," team member Ian Roberts of the Waterloo Centre for Astrophysics in the Faculty of Science in the UK, said in a statement. "Early on in our search of the JWST data, we spotted a distant, undocumented jellyfish galaxy that sparked immediate interest."
The JWST image of COSMOS2020-635829 shows a galactic disk that appears relatively normal, not dissimilar from our own modern-day galaxy, barring the distinct gas trails. Bright blue "knots" can be seen in these tendrils that represent groupings of young stars. Similar features can be seen in the Hubble Space Telescope image of a similar jellyfish galaxy, seen above.
The youth of these stellar bodies implies that they were born outside the main galactic disk of COSMOS2020-635829 within these tendrils of ram-stripped gas. While this phenomenon is expected of jellyfish galaxies, the image of COSMOS2020-635829 has delivered at least one surprise. Previously, researchers had thought that still-forming galaxy clusters that existed 8.5 billion years or so ago would not commonly produce the pressure that leads to ram-stripping.
"The first is that cluster environments were already harsh enough to strip galaxies, and the second is that galaxy clusters may strongly alter galaxy properties earlier than expected," Roberts explained. "Another is that all the challenges listed might have played a part in building the large population of dead galaxies we see in galaxy clusters today. This data provides us with rare insight into how galaxies were transformed in the early universe."
The team now intends to continue studying COSMOS2020-635829 with the JWST, hoping to solve further mysteries regarding this and other jellyfish galaxies.
The team's results were published on Tuesday (Feb. 17) in The Astrophysical Journal.
Editor's Note (02/19/26): The article was updated to reflect the fact that the featured image was captured by the Hubble Space Telescope
