A galaxy named Hebe, observed 400 million years after the Big Bang, shows evidence of pristine Population III stars formed solely from hydrogen and helium. Researchers led by Roberto Maiolino at the University of Cambridge used the James Webb Space Telescope to confirm spectral lines indicating extremely hot, massive stars. The finding offers insights into the early universe's star formation.
Astronomers have identified what may be the strongest evidence yet for Population III stars, the universe's earliest stellar generation. These stars, theorized to be hundreds of times more massive and tens of thousands of degrees hotter than the Sun, formed from nearly pure hydrogen and helium without heavier elements. The galaxy Hebe, detected by the James Webb Space Telescope, displays no detectable metals beyond these basics and features light concentrated at frequencies linked to ionized helium—a signature of ultra-hot stars, according to Roberto Maiolino at the University of Cambridge and his team. “It seems that Population III stars is, as far as we can see, the most plausible explanation,” Maiolino said. “All other explanations are highly unsatisfactory.” Hebe was first spotted by Maiolino's group in 2024, with initial spectra hinting at an ionized helium line. Further James Webb observations revealed a matching ionized hydrogen line from the same source, solidifying the detection. Team member Hannah Übler at Ludwig Maximilians University of Munich described scrutinizing the data extensively: “Once this was clear... it was a great moment to know... that here we have helium and hydrogen, suggesting the Population III scenario.” While compelling, the evidence is not definitive. Daniel Whalen at the University of Portsmouth noted the ionized helium implies hot objects but lacks precision to exclude trace heavier elements, potentially indicating slightly younger Population II stars. Simulations also suggest early stars formed in sparse clusters, challenging a galaxy teeming with them. Maiolino emphasized the broader value: “It’s not just about... saying we found it... we are learning already a lot.” The team’s models estimate these stars were mostly 10 to 100 times the Sun’s mass.