Celestial Newborn: Stars of Pure Hydrogen express
A bonfire built of pure alcohol burns hot and gives off almost no smoke. That's roughly how the first stars shone: they contained no heavy elements, only hydrogen and helium left over from the Big Bang. The James Webb Space Telescope may have caught one such "bonfire" in the galaxy GN-z11. We see it as it was 400 million years after the birth of the universe.
In the spectrum of a tiny bright region named Hebe, astronomers found a strong ionized helium line at a wavelength of 1640 angstroms. It's like a fingerprint left by extremely hot ultraviolet radiation. No heavy elements were detected — only an upper limit. This means the source is either nearly pristine, or we are seeing light from a cluster of so-called Population III stars. These are the first hypothetical luminaries, assembled from the primordial mix of gases.
The authors compared their observations with computer models of star cluster formation in the early universe. It turns out that Hebe could contain several hundred thousand solar masses — roughly 300 000 Suns packed into a tight swarm. This is at the limit of what the standard model allows for the formation of the first stars. An alternative, an accreting supermassive black hole, also produces hard radiation. But its ultraviolet "signature" fits the measured helium and hydrogen lines less well. A black hole heats the surrounding gas differently, and the calculated brightness of recombination lines diverges from the observations.
So Hebe is most likely a true celestial newborn: a star cluster ignited in an era when the periodic table was nearly empty. Its light has traveled 13,4 billion years, almost the entire age of the universe, to tell us how it all began.
Original abstract
as written by the authors arXiv:2604.19075
Recent high-resolution spectroscopy with the James Webb Space Telescope (JWST) has confirmed the presence of a strong He II $$\lambda1640$$ emitting clump in the vicinity of GN-z11, with only upper limits on its metallicity. To explain the peculiar properties of this source, now termed Hebe, a cluster of metal-free, Population III (Pop III) stars has been invoked. A less likely source for the hard UV ionizing radiation could be an accreting supermassive black hole (SMBH) embedded inside Hebe. We here provide further constraints on what could power the observed emission lines in Hebe. Comparing with cosmological simulations of Pop III star cluster formation, we assess the maximum Pop III stellar mass that could plausibly form at the location of Hebe, finding stellar masses of a few $$10^5\,M_{\odot}$$, consistent with those inferred from the observations. Modeling the continuum spectral energy distribution arising from an accreting SMBH, we derive He II and H I ionizing rates and the resulting recombination line luminosities, providing a less natural fit for the combined observations. We thus confirm the interpretation of Hebe as a remarkable, primordial object, with the most plausible power source provided by a massive cluster of Pop III stars, at the limit of what is allowed within the standard model of first star formation.
The helium line He II λ1640 spotted by Webb is a hundred times 'harder' than ordinary ultraviolet: emitting it requires temperatures above 50,000 degrees — like the surface of the hottest known stars.
In Isaac Asimov's novel 'The Gods Themselves', creatures from a parallel universe are described where stars are made of pure hydrogen — almost like the hypothetical Population III stars, except there they follow different laws of physics.