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Many millions of years after the big bang, a point of light arose in a dark universe. This first star began to blast out radiation, which knocked electrons off the surrounding fog of hydrogen. More stars formed, turning nearly all the neutral hydrogen atoms, which had previously absorbed some wavelengths of light, into a fully transparent broth of ionised hydrogen. Light could then travel freely through the expanding cosmos: this was the end of the cosmic dark ages and the start of galaxy formation.

These first stars and the galaxies they formed were very different from anything we see in the modern universe. For one, they were made almost entirely of hydrogen and helium, with trace amounts of lithium, because no heavier elements existed yet. “The chemistry that we see can only be made in stars,” says at University College London.

Up until 2022, the oldest known galaxy was one called GN-z11, which formed about 400 million years after the big bang. We know this because of a property called redshift: the expansion of the universe means that the more distant an object is, the faster it is moving away from us, and the quicker this motion, the redder its light becomes. Light takes time to travel, so the more distant an object is – and the higher its redshift – the earlier in the universe’s history we are seeing it. GN-z11 has a redshift of about 11.

However, thanks to the James Webb Space Telescope (JWST), we now know there are galaxies that are much more ancient than GN-z11. JWST is larger and more sensitive than any telescope that came before, so it has vastly improved our view into the early universe since its launch in 2021. That deeper look has shown an unexpected abundance of large galaxies in the first billion years after the big bang.

We can’t see the very first galaxies directly yet, and we may never be able to, but JWST is getting closer and closer. The earliest galaxy with a confirmed distance has a redshift of around 14, placing it about 290 million years after the big bang. It probably formed at least 100 million years earlier, though, says at the University of Arizona. “Three years ago, I would’ve said the first galaxies were forming at a redshift of 15 to 20, and now I would say 20 to 30,” says at the University of California, Santa Cruz. A redshift of 30 indicates formation around 100 million years after the big bang. “It’s clear that things happened quicker than we expected,” he says.

James Webb Space Telescope

We aren’t entirely sure why that is, but conditions in the early universe – relatively dense, without old stars or heavy elements – could have allowed galaxies to form faster than they do in the modern cosmos. “The JWST observations are changing the underpinnings of how galaxies form,” says Illingworth.

That could force us to rethink the development of the early universe and how matter behaved there. “We can use these galaxies to test our ideas about how the universe is operating,” says at the US National Radio Astronomy Observatory in Virginia.

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So, finding the first galaxies and working out how they formed gives us insight into the state of the early cosmos writ large, but that isn’t all. Those galaxies played host to the stars that forged the chemical elements that make up life as we know it and, indeed, even our own bodies. “When we look at these early galaxies,” says Hainline, “it’s a direct link to who we are and where we came from.”

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