A cosmic dance that shapes the fate of both galaxies
Fifty-nine million light-years away in Ursa Major, a small and ancient-looking galaxy called I Zwicky 18 is doing something remarkable: it is being born, again. The James Webb Space Telescope, using infrared light invisible to its predecessors, has caught this dwarf galaxy mid-starburst in March 2024, revealing conditions that echo the universe's earliest epochs. Pulled into creative frenzy by the gravitational embrace of a smaller companion, I Zwicky 18 reminds us that galaxies are not solitary monuments but living, relational things — shaped as much by their neighbors as by their own histories.
- A galaxy long thought to be a relic of the early universe is actively forging new stars right now, upending assumptions about its age and activity.
- JWST's infrared vision cuts through what Hubble could not see, exposing star formation far more recent than the one-to-ten-billion-year estimates previously on record.
- A smaller companion galaxy orbits nearby, its gravitational pull compressing gas clouds and igniting waves of stellar birth — a cosmic trigger hiding in plain sight.
- Two blazing regions of young, hot stars push heated gas outward in bubble-shaped filaments, sculpting the galaxy's structure in real time.
- Behind the drama of I Zwicky 18, hundreds of distant background galaxies glow red and orange with cosmic redshift, framing this local starburst within the staggering depth of an expanding universe.
In the constellation Ursa Major, a small irregular galaxy known as I Zwicky 18 is caught in a moment of violent creation. When the James Webb Space Telescope turned its infrared gaze toward this dwarf galaxy in March 2024, it found something unexpected: not a quiet relic of the ancient universe, but a galaxy actively and dramatically forging new stars. Poor in heavy elements and smaller than the Milky Way, I Zwicky 18 had long fascinated astronomers for resembling the primitive galaxies of the early universe. JWST confirmed that resemblance — and then revealed something far more immediate.
At the galaxy's core, two bright regions burn with clusters of young, hot stars, the newest concentrated in the northwestern section. Around them, brown filaments of gas trace the outlines of expanding bubbles, material driven outward by stellar winds and intense ultraviolet radiation. Where Hubble's visible-light observations had suggested star formation dating back billions of years, JWST's infrared sensitivity uncovered activity far more recent, indicating the starburst is still very much underway.
The likely cause sits just below the main galaxy in the image: a smaller companion, a loose collection of blue stars bound in orbit around its larger neighbor. Astronomers believe the companion's gravitational pull compresses I Zwicky 18's gas clouds, triggering successive waves of star formation — a reminder that galaxies evolve through relationship, not in isolation.
The galaxy carries the name of Swiss astronomer Fritz Zwicky, who catalogued it in the 1930s. More than ninety years later, it remains one of the most compelling targets in the sky. The new JWST image, part of a program tracing the life cycle of dust, places I Zwicky 18 against a backdrop of hundreds of distant galaxies — their light stretched red and orange by cosmic expansion — a humbling reminder that this small, furious act of creation is unfolding within an incomprehensibly vast universe.
Fifty-nine million light-years away, in the constellation Ursa Major, a small galaxy is in the throes of creation. The James Webb Space Telescope has captured it mid-starburst—a moment of intense stellar birth that astronomers say mirrors the conditions of the early universe itself. The galaxy, known as I Zwicky 18, is an irregular dwarf, smaller than our Milky Way and remarkably poor in heavy elements. Those characteristics alone make it a window into how galaxies behaved billions of years ago. But what JWST revealed in its infrared observations, released in March 2024, was something more immediate and dramatic: evidence that this ancient-looking galaxy is actively, violently creating new stars right now.
Looking at the galaxy's core, two bright regions stand out, each studded with young stars burning exceptionally hot. The newest stars appear to cluster in the northwestern section. Around both regions, brown filaments trace the shape of gas bubbles—material heated and pushed outward by stellar winds and the intense ultraviolet radiation pouring from those young, massive stars. It is a portrait of creation in real time, rendered in infrared light that Hubble's visible-light observations could not fully capture. Where Hubble had detected hints of older star formation dating back one to ten billion years, JWST's infrared eyes revealed much more recent activity, suggesting the galaxy's starburst is ongoing.
The question of why I Zwicky 18 is creating stars so vigorously points to a companion. Just below the main galaxy in the image sits another, smaller galaxy—a collection of blue stars orbiting its larger neighbor. Astronomers suspect that the gravitational pull of this nearby companion is the trigger. As the smaller galaxy orbits, its gravity tugs at I Zwicky 18's material, compressing gas clouds and igniting waves of star formation. It is a cosmic dance that shapes the fate of both galaxies, a reminder that galaxies do not evolve in isolation.
The galaxy itself carries the name of its discoverer, Fritz Zwicky, a Swiss astronomer who identified it in the 1930s. Zwicky's catalog of unusual objects has proven enduring; more than ninety years later, his I Zwicky 18 remains one of the most intriguing targets for modern telescopes. The new JWST image is part of a broader program designed to trace the life cycle of dust within the galaxy, building on decades of observation and adding layers of detail that were invisible before.
What makes the image even more striking is what surrounds I Zwicky 18 and its companion. In the top-right corner, a single star sits in the foreground, its diffraction spikes sharp and clear. But beyond it, filling the background, are hundreds of other galaxies—oval-shaped, distant, some white and others tinted orange or red by the cosmic redshift that comes with distance. Those background galaxies are so far away that their light has been stretched toward the infrared end of the spectrum, a visible reminder of the universe's expansion and the sheer depth of space. I Zwicky 18, for all its drama and youth, is merely one small actor in an incomprehensibly vast scene.
Notable Quotes
The galaxy's low content of heavy elements makes it typical of galaxies that existed in the early universe— European Space Agency description of JWST observations
The Hearth Conversation Another angle on the story
Why does a dwarf galaxy matter? Isn't it just a smaller version of something we already understand?
Not quite. I Zwicky 18 is small, yes, but it's chemically primitive—almost no heavy elements. That makes it a living fossil. Most galaxies we see have been enriched by billions of years of stellar death and recycling. This one hasn't. It's like finding a corner of the universe that never aged.
And the starburst? Why is that surprising?
Because JWST saw it happening now, not in the distant past. Hubble had hints of old star formation, but the infrared data shows the galaxy is actively making stars today. That's the puzzle—why is something so ancient-looking so alive?
The companion galaxy—is that the answer?
Likely part of it. Gravity from the nearby galaxy is probably squeezing gas clouds in I Zwicky 18, triggering collapse and ignition. But we don't fully understand the mechanism yet. That's what makes the image so valuable.
What does this tell us about the early universe?
If I Zwicky 18 resembles early galaxies in its composition and behavior, then maybe those ancient galaxies were more dynamic than we thought. Maybe starbursts were common. JWST is letting us test that hypothesis in ways we couldn't before.
So this is really about time travel.
In a sense, yes. We're seeing a galaxy that looks like it should be from the early universe, but it's close enough to study in detail. That's the gift of JWST—it collapses distance and time in a way that lets us learn.