Webb Telescope Spots Most Distant Jellyfish Galaxy Yet

A Cosmic Jellyfish from the Dawn of the Universe

A team of astrophysicists from the University of Waterloo, using the James Webb Space Telescope (JWST), has discovered the most distant jellyfish galaxy to date — an object designated COSMOS2020-635829, located at a distance of 8.5 billion light-years. The light captured by the telescope left this galaxy when the universe was only about half its current age. The results of the study were published in the scientific journal Astrophysical Journal.

What are Jellyfish Galaxies?

Jellyfish galaxies get their poetic name from the long, tentacle-like streamers of ionized gas and newborn stars that trail behind them as they move through dense galaxy clusters. This phenomenon is technically called ram-pressure stripping: the hot, rarefied gas filling the galaxy cluster acts like a strong wind, literally tearing gas away from the moving galaxy.

The main body of COSMOS2020-635829 looks like a normal, symmetrical disk galaxy. But in its wake — far from the galactic core — bright blue clumps shine. These are extremely young stars, less than 100 million years old, that formed directly in the stripped gas outside the main galactic disk.

Why is the Discovery Surprising?

Scientists previously assumed that galaxy clusters in such an early stage of the universe were not yet dense and hot enough to produce intense ram-pressure stripping. The new finding challenges this assumption.

"The first conclusion is that the cluster environment was already harsh enough to strip galaxies at that time. The second is that galaxy clusters may have significantly altered the properties of galaxies earlier than we thought," explained lead author of the study, Dr. Ian Roberts, a postdoctoral researcher at the Waterloo Centre for Astrophysics, to Phys.org.

The research also shows that ram-pressure stripping not only tears away gas but can also compress it and trigger intense star formation — adding another dimension to our understanding of galaxy evolution.

Still Just a Candidate

Despite the remarkable results, scientists emphasize caution: COSMOS2020-635829 is so far only a candidate jellyfish galaxy. Dr. Roberts and his team have requested further observing time on JWST to examine the object in more detail using spectroscopy and definitively confirm its character.

A New Window into the History of the Universe

Since its launch in 2022, the James Webb Telescope has repeatedly proven to be a revolutionary instrument — its infrared imaging can penetrate through clouds of dust and see galaxies in their earliest stages. The discovery of the most distant jellyfish galaxy is another example of how JWST is rewriting textbook knowledge about cosmic evolution and forcing scientists to reconsider when and how large structures form in the universe.