The first generation of stars that were born in the universe are a mystery. We can estimate when they existed and even how big they might have gotten, but direct evidence has been lacking. Now, JWST has found the most compelling proof of their existence, reporting a crucial signature of their presence in galaxy GS 3073.

The light of this galaxy comes from just over 1 billion years after the Big Bang. Using JWST, researchers were able to estimate the chemical composition of stars in this distant galaxy and found something extremely peculiar: an imbalance in the ratio of nitrogen to oxygen. This has been seen as evidence of the first stars, known as Population III.

Following the Big Bang, only three elements were created: hydrogen, helium, and a sprinkling of lithium. All the other elements we find in nature were formed in stars and stellar interactions. It took tens, if not hundreds, of millions of years for stars to form though, and many of those stars were truly massive. They are expected to weigh between 1,000 and 10,000 times the mass of the Sun.