Researchers at the University of Waterloo have identified the farthest jellyfish galaxy ever observed. The discovery was made using deep space observations from the James Webb Space Telescope (JWST).
Jellyfish galaxies get their name from the long, flowing streams of gas that stretch out behind them, resembling tentacles. These galaxies race through crowded galaxy clusters filled with extremely hot gas. As they move, that surrounding gas pushes against them like a powerful headwind, sweeping their own gas backward into trailing strands. Astronomers call this process ram-pressure stripping.
This newly identified galaxy sits at z = 1.156, which means its light has traveled for 8.5 billion years to reach us. In other words, we are seeing it as it appeared when the universe was much younger.
The observation offers an unusual glimpse into how galaxies were reshaped long ago and raises new questions about what conditions were really like 8.5 billion years in the past.
A Clear View Into the Distant Universe
The team uncovered the galaxy while studying the COSMOS field — Cosmic Evolution Survey Deep field — a region of the sky that has been examined extensively by multiple telescopes. Astronomers selected this area because it lies far from the crowded plane of the Milky Way, reducing interference from nearby stars and dust. It is also positioned so that telescopes in both hemispheres can observe it, and it lacks bright foreground objects that might block the view. This makes it an ideal window into the distant universe.
“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,” said Dr. Ian Roberts, Banting Postdoctoral Fellow at the Waterloo Centre for Astrophysics in the Faculty of Science. “Early on in our search of the JWST data, we spotted a distant, undocumented jellyfish galaxy that sparked immediate interest.”
Bright Blue Star Formation in Stripped Gas
The galaxy itself has a fairly typical disk shape. What makes it stand out are the bright blue clumps scattered along its trailing streams. These glowing knots are extremely young stars. Their ages indicate they likely formed outside the main body of the galaxy, within the gas that was pushed away. That type of star formation is consistent with what astronomers expect in jellyfish galaxies experiencing ram-pressure stripping.
Rethinking Galaxy Clusters in the Early Universe
Studying this object has challenged previous assumptions about the early universe. Many scientists believed that galaxy clusters at that time were still assembling and that ram-pressure stripping was relatively rare. The new findings suggest otherwise.
“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 said. “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.”
If confirmed by further research, these results could reshape understanding of how dense cosmic environments influenced galaxy evolution billions of years ago.
To investigate further, Roberts and his colleagues have applied for additional observing time with JWST to explore this galaxy in greater detail.
The study, “JWST Reveals a Candidate Jellyfish Galaxy at z=1.156,” was published in The Astrophysical Journal.
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