After the Big Bang, space was filled only with hydrogen and helium. From these, the first stars began to be born — giants entirely devoid of heavy elements (astronomers call this lack of metals). Their short lives ended in explosions, scattering the first batches of heavy atoms and creating primordial nebulae.

Their light is almost indistinguishable — it gets lost in the glare of other galaxies, like a whisper in a crowded room. To hear it, astronomers turned to pixel-by-pixel analysis. The James Webb Space Telescope breaks the image into pixels, and a program with machine learning, trained on millions of computer simulations, compares the breakdown of light by color in each pixel to a model, accounting for distances where light reddens due to the expansion of the universe.

This led to the identification of candidate "Blueberry": in the central pixel, its spectrum consists solely of helium and hydrogen, without the slightest trace of metals. This is the first reliably identified Population III star. The method paves the way for mapping the era of heavy element formation and, possibly, solving the mystery of supermassive black holes at galactic centers. James Webb will continue the search.