A bonfire built of pure alcohol burns hot and gives off almost no smoke. That's roughly how the first stars shone: they contained no heavy elements, only hydrogen and helium left over from the Big Bang. The James Webb Space Telescope may have caught one such "bonfire" in the galaxy GN-z11. We see it as it was 400 million years after the birth of the universe.

In the spectrum of a tiny bright region named Hebe, astronomers found a strong ionized helium line at a wavelength of 1640 angstroms. It's like a fingerprint left by extremely hot ultraviolet radiation. No heavy elements were detected — only an upper limit. This means the source is either nearly pristine, or we are seeing light from a cluster of so-called Population III stars. These are the first hypothetical luminaries, assembled from the primordial mix of gases.

The authors compared their observations with computer models of star cluster formation in the early universe. It turns out that Hebe could contain several hundred thousand solar masses — roughly 300 000 Suns packed into a tight swarm. This is at the limit of what the standard model allows for the formation of the first stars. An alternative, an accreting supermassive black hole, also produces hard radiation. But its ultraviolet "signature" fits the measured helium and hydrogen lines less well. A black hole heats the surrounding gas differently, and the calculated brightness of recombination lines diverges from the observations.

So Hebe is most likely a true celestial newborn: a star cluster ignited in an era when the periodic table was nearly empty. Its light has traveled 13,4 billion years, almost the entire age of the universe, to tell us how it all began.