A Galaxy That Looks Like a Jellyfish Is Helping Scientists See 8.5 Billion Years Into the Past
A cosmic 'jellyfish' spotted deep in space is revealing surprising clues about the universe’s past
When you gaze up at the night sky, you’re looking back in time. Light from the stars takes years, sometimes millennia, to reach your eyes.
Now imagine seeing light that’s been traveling for 8.5 billion years—more than half the age of the universe.
That’s what a team of astrophysicists just accomplished, and what they found in that ancient glow is breathtaking: a galaxy that looks like a jellyfish drifting through the ocean of space.
A galaxy with tentacles made of baby stars
The nickname “jellyfish galaxy” is wonderfully descriptive. A jellyfish galaxy is a type of galaxy found in dense clusters that appears to be “dripping” gas, forming long, tentacle-like tails of newborn stars trailing behind it.
Picture an actual jellyfish gliding through deep water, translucent tendrils streaming in its wake. Now scale that image up to something the size of a galaxy drifting in space.
The process creating those graceful tails is anything but gentle, though.
A violent mechanism called ram-pressure stripping is at work: the hot, dense material between galaxies in a cluster pushes against a galaxy as it moves, tearing away its gas.
Think of it like a cosmic headwind—the surrounding material acts like a powerful gale, ripping gas from the galaxy and sculpting it into those dramatic trailing tails.
What’s happening inside those tails is where it gets really fascinating. This newly discovered galaxy, named COSMOS2020-635829, has a normal disc structure with bright blue knots within its gas trails.
Those blue knots are very young stars, and their presence means stars are forming outside the main galaxy within the stripped gas. New stars are being born in the galaxy’s wake—life emerging from destruction.
The James Webb Telescope made it all possible
None of this would be visible without the James Webb Space Telescope (JWST).
If you remember watching the Apollo missions or following the Hubble Space Telescope’s stunning images over the decades, Webb represents the next leap forward.
Launched on December 25, 2021, the JWST is the largest, most powerful infrared space observatory ever sent into orbit. Designed by NASA, ESA, and CSA, it orbits the sun one million miles from Earth, using a 6.5-meter gold-coated mirror to peer through cosmic dust and observe the very first galaxies formed after the Big Bang.
Its infrared capabilities let it see things that were simply invisible before, including galaxies so ancient and so distant that their light has been stretched into infrared wavelengths by the expansion of the universe.
That power is exactly what allowed astrophysicists from the University of Waterloo to spot COSMOS2020-635829, the most distant jellyfish galaxy ever observed.
Peering 8.5 billion years into the past
The new galaxy discovered has a redshift of z = 1.156, meaning astronomers are seeing it as it existed about 8.5 billion years ago.
Here’s a way to wrap your mind around that number: when the light from this jellyfish galaxy first began its journey toward us, our own sun and solar system did not yet exist. Earth wouldn’t form for roughly another four billion years.
The galaxy was identified in the COSMOS field (Cosmic Evolution Survey Deep field), a region that astronomers study frequently.
It sits far from the Milky Way’s plane, with minimal interference from nearby stars and dust, providing a clear view of distant galaxies. The area is visible from both hemispheres, making it one of the cleanest windows astronomers have into the deep 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, in a news release.
“Early on in our search of the JWST data, we spotted a distant, undocumented jellyfish galaxy that sparked immediate interest,” Roberts added.
Three discoveries that shake up what scientists thought they knew
Finding the galaxy alone would have been remarkable. But the team uncovered three additional results that push the timeline of cosmic evolution further back than scientists previously expected.
“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, per the release.
That means the violent forces that shape and sometimes destroy galaxies were already at work in the universe’s relative youth—billions of years earlier than many models had suggested.
“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,” he added.
“Dead galaxies”—galaxies that have stopped forming new stars—are one of the enduring puzzles of modern astrophysics. Galaxy clusters today are full of them.
What COSMOS2020-635829 suggests is that the process of stripping away the gas a galaxy needs to birth new stars may have been underway far earlier in cosmic history than previously understood.
The question of how those galaxies died is getting a new, much older chapter.
Why this discovery stirs the imagination
Every time the James Webb Space Telescope delivers a finding like this, it reshapes our picture of how the universe evolved—how galaxies were born, changed, and how some of them died.
For a publicly funded telescope built through international partnership, each discovery is a return on that investment, paid in knowledge.
COSMOS2020-635829, that distant jellyfish trailing its luminous tentacles through a galaxy cluster 8.5 billion years in the past, tells us the universe is still full of surprises. And thanks to Webb, we are only beginning to see them.
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