Light from the very first stars in the universe has been measured – and there is less of it than previously thought. The discovery should help us better understand how the hot haze of hydrogen that existed shortly after the big bang transformed into the complex web of stars and galaxies we see today.

Although the first stars are too distant to be glimpsed directly, their light contributes to a diffuse fog of photons known as the extragalactic background light, which permeates the universe. The intensity of this light through cosmic time holds a record of all the stars that have ever existed.