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 opaque, neutral hydrogen atoms into a transparent broth of ionised hydrogen, so that light could 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 Richard Ellis 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…
