Tracing the first stars with cosmic infrared background fluctuations

The deepest space and ground-based observations find metal-enriched galaxies at cosmic times when the Universe was < 1 Gyr old. These stellar populations had to be preceded by the metal-free first stars, Population III. Recent cosmic microwave background polarization measurements indicate that stars started forming early when the Universe was < ∼ 200 Myr old. Theoretically it is now thought that Population III stars were significantly more massive than the present metal-rich stellar populations. While such sources will not be individually detectable by existing or planned telescopes, they would have produced significant cosmic infrared background radiation in the near-infrared, whose fluctuations reflect the conditions in the primordial density field. Here we report a measurement of diffuse flux fluctuations after removing foreground stars and galaxies. The anisotropies exceed the instrument noise and the more local foregrounds and can be attributed to emission from massive Population III stars, providing observational evidence of an era dominated by these objects.