Astronomers have discovered the most distant spiral galaxy ever seen, and it appears to be much more evolved than thought possible.
It exists just one billion years after the Big Bang, and is showing a surprisingly mature structure.
Named Zhúlóng — meaning ‘Torch Dragon’ in Chinese mythology – the galaxy was discovered as part of the PANORAMIC Survey by a team of astronomers led by Christina Williams.
A look back in time
Because light takes time to travel across the Universe, when we look at objects in space that are millions or billions of lightyears away, that means we're seeing them as they existed millions or billions of years ago.
In this way, astronomers can effectively look back in time by peering deeper into the Universe with powerful telescopes.
They can even see objects as they existed soon after the Big Bang, which occurred 13.8 billion years ago.
Zhúlóng is a spiral galaxy that appears to astronomers as it did just one billion years after the Big Bang, and it's much more mature than expected.
Huge spiral galaxies are a common sight in images of the Universe.
But structures as large and intricate as these take time to form, over billions of years.
They've proven difficult to find in the early Universe, which is what you would expect, as huge galaxies with sprawling spiral arms should take billions of years to form.
Yet astronomer Christina Williams of NSF NOIRLab discovered this surprisingly mature spiral galaxy just one billion years after the Big Bang.
It's the most distant, earliest known spiral galaxy in the Universe.
It was discovered as part of the PANORAMIC Survey, conducted with the James Webb Space Telescope and co-led by Williams and Pascal Oesch of the University of Geneva.
The purpose of the observations is to conduct a wide-area survey of the sky using the Webb Telescope that will prepare for future wide-area surveys by NOIRLab, like the Legacy Survey of Space and Time (LSST), by the Rubin Observatory.
"Wide-area surveys are necessary to discover rare, massive galaxies," says Williams, co-author of the study paper.
"We were hoping to discover massive and bright galaxies across the earliest epochs of the Universe to understand how massive galaxies form and evolve, which helps to interpret the later epochs of their evolution that will be observed with the LSST."
Why Zhúlóng is so surprising
Astronomers say Zhúlóng "has a surprisingly mature structure that is unique among distant galaxies, which are typically clumpy and irregular".
In fact, the galaxy looks more like galaxies found in the nearby Universe and is similar in mass and size to our own Milky Way.
Also, it shows a mixture of old stars and younger stars; the older ones compacted into a central bulge and younger ones peppered throughout its spiral arms.
This, say astronomers, shows that mature galaxies can develop earlier in the Universe than previously thought possible.
Similarly, galaxies' spiral arms can develop on shorter timescales than thought possible.
"It is really exciting that this galaxy resembles a grand-design spiral galaxy like our Milky Way," says Williams.
"It is generally thought that it takes billions of years for this structure to form in galaxies, but Zhúlóng shows that this could also happen in only one billion years."
The team say the rarity of galaxies like Zhúlóng suggests these galactic spiral structures don't last long at this chaotic time in the early Universe.
Galactic collisions and mergers were more common at this point in our cosmic timeline, and could be responsible for the scarcity of mature structures like those seen in galaxy Zhúlóng.
Spiral structures may be more stable later on in the Universe, which is why they're more common in our cosmic neighbourhood.
The team say future Webb and Atacama Large Millimeter/submillimeter Array observations will help them learn more about the Zhúlóng galaxy’s properties and how it formed.
Read the full paper at www.aanda.org/articles/aa/abs/2025/04/aa53487-24/aa53487-24.html
