When we look at the stars, we often forget that we are also looking back in time. The farther we look, the further back in billions of years we travel. But what happens when this time travel brings us face to face with the impossible? That is exactly what happened when the telescope James Webb captured the image of Zhulong, an ancient galaxy from a time when the universe was just a billion years old. The problem? Zhúlóng is a perfect spiral galaxy, with well-defined arms, a central bulge, and an extended disk of stars: practically a carbon copy of our Milky Way.
According to all models of galaxy formation, such a mature and orderly structure It shouldn't exist so “soon” after the Big Bang. Early galaxies should be small, chaotic, and shapeless. Yet there it is, with its disk stretching over 60.000 light-years and a stellar mass of over 100 billion suns. A cosmic dragon that is burning our astronomical certainties.
The discovery that turns everything upside down
Traditional astronomical theories have always held that large, structured galaxies like the Milky Way took billions of years to form. First small irregular galaxies, then cosmic mergers, and only after a long process of growth and evolution, the formation of the elegant spirals that dot the present universe.
But Zhúlóng decided not to follow the script. This ancient galaxy was spotted at a redshift of 5.2, which places it just a billion years after the Big Bang. Yet it displays features that should only appear in much more mature galaxies.
The image of Zhúlóng shows its spiral arms, an old central bulge, and a large star-forming disk, resembling the Milky Way.
I wonder what the astronomers of the PANORAMIC program thought (you can find the paper here) when they first saw that data. They probably rubbed their eyes in disbelief, thinking it was an observational error.
Ancient Zhúlóng Galaxy, a Solar Dragon in Cosmology
Mengyuan Xiao, postdoctoral researcher at the Department of Astronomy of the Faculty of Sciences of theUniversity of Geneva and lead author of the study, explains the origin of the name:
We named this galaxy Zhúlóng, which means 'Torch Dragon' in Chinese mythology. In myth, Zhúlóng is a powerful red solar dragon that creates day and night by opening and closing its eyes, symbolizing light and cosmic time.
The choice of name couldn’t be more appropriate. Like the mythical dragon that plays with time, this ancient galaxy is forcing astronomers to reconsider their understanding of cosmic timelines.
What makes Zhúlóng so special is how similar it is to our own galaxy in shape, size, and stellar mass. Its disk spans over 60.000 light-years, comparable to the Milky Way, and contains more than 100 billion solar masses in stars. A true cosmic twin.
A lucky discovery
Zhúlóng was identified through JWST's PANORAMIC program, a project led by Christina Williams (NOIRlab) to Pascal Oesch (UNIGE). PANORAMIC uses the JWST’s “pure parallel” mode, which allows high-quality images to be collected while the telescope’s main instrument is collecting data on another target.
This allows JWST to map large areas of the sky, which is essential for discovering massive galaxies, as they are incredibly rare.
It's fascinating how sometimes the most important discoveries happen almost by accident, while you're observing something else. Pascal Oesch, associate professor at theUniversity of Geneva, known as:
This discovery shows how the JWST is fundamentally changing our view of the early universe.
It's not the first time that the James Webb telescope is reshaping our understanding of the cosmos. Since it became operational, it has revealed massive, well-structured galaxies that formed much earlier than previously thought possible.
With future observations from JWST and byLarge Millimeter Array Atacama (SOUL), astronomers hope to further confirm Zhúlóng's properties and reveal more about its formation history. In the meantime, as new, large-scale surveys by JWST continue, we expect to find more similar galaxies, offering new insights into the complex processes that shape galaxies in the early Universe.
And perhaps, in a few years, we will look back on this discovery and wonder how we could have thought that the young universe was just a chaotic and messy place, when in fact it was already full of elegant and ordered structures like Zhúlóng.
