In the dark room of the early Universe, the first spark flickered. A few hundred million years after the Big Bang, when space was filled only with hydrogen and helium, Population III stars were born: metal-free giants whose light first tore through the primordial darkness. They have been sought for a long time, but all candidates were too massive, requiring star clusters of hundreds of thousands or millions of solar masses, which contradicted theory. Now, in the galaxy LAP1-B, magnified by gravitational lensing from the cluster MACS J0416, the James Webb Space Telescope has found an object that matches all three key predictions for the first time.

The spark metaphor is apt. LAP1-B is not a huge bonfire but a small flame: about 1500 solar masses, corresponding to roughly 38 stars of 40 solar masses each. The observed Hα line flux agrees with this mass given a lensing magnification of μ=100 and an escape fraction of ionizing photons of 10%. The virial temperature of the halo, about $10^4$ K, is exactly the environment where calculations say the first stars should form. This is no coincidence: a semi-analytic model based on N-body simulations with a resolution of 8000 solar masses per particle predicts precisely these conditions at redshift z≈6.6.

What does this change? Previously, it was unclear whether Population III stars actually exist and how to distinguish them from later Population II stars. Now LAP1-B has become a benchmark: its properties agree with the model in halo mass, stellar mass, and metallicity. This removes the main objection against previous candidates, namely the excessively large required mass. Moreover, the cumulative number of sources behind the cluster MACS J0416 is calculated to be 0.88 in the redshift range z=5.9–6.6, meaning that finding such an object was expected, not a miracle.

The dark room is beginning to fill with light. Looking ahead, more sensitive observations are planned: the model predicts that with a tenfold increase in sensitivity, more than a dozen Population III sources could be found by z=10. Detailed hydrodynamic simulations of clusters of such stars in atomic-cooling halos and their transition to Population II stars will help clarify how often the first stars formed in mixtures with metal-enriched gas. LAP1-B is the first spark, but not the last: it illuminates the path to understanding how the Universe emerged from darkness.