Candidate system appears chemically intact just 450 million years after the Big Bang
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There’s a new contender for the universe’s first generation stars.
A bright cluster observed around 450 million years after the Big Bang has the chemical characteristics of first generation stars — notably that it does not seem to contain any element heavier than helium. This identification, reported in three papers submitted March 20 to arXiv.org, provides evidence for these pristine stars much earlier than previous candidates.
The first generation stars, known as population III stars, would likely have been massive – up to 1,000 times the mass of the sun – and very bright. These stars were born with only elements created in the Big Bang: hydrogen, helium and a tiny quantity of lithium. In contrast, the stars we see in the night sky also contain heavier elements forged and passed down from previous generations of stars.
Astronomers think the first of the first generation stars formed a few hundred million years after the Big Bang – more than 13.5 billion years ago. But until now, researchers had only noticed the existence of such stars about 1 billion years after the beginning of the universe. The new report of much older candidates increases astronomers’ confidence that they can find more such systems in the early universe, says astronomer Seiji Fujimoto of the University of Toronto, who was not involved in the research.
The cluster, which astronomers have nicknamed Hebe (named partly for the goddess of youth in Greek mythology, partly after the technical name for one of the wavelengths of light it emits), was first spotted in 2024. At the time, astronomers lacked evidence to determine the nature of the object. So, in 2025, they carried out higher resolution observations with the James Webb Space Telescope.
To determine whether a candidate is a first-generation star, astronomers first look for evidence of the presence of elements heavier than helium. Hebe not only showed no trace of heavier elements but also emitted light specific to highly energetic helium and hydrogen. This light, emitted by the gas clouds, indicates that the cluster contains one or more objects emitting very high energy radiation.
“This is a textbook case for the first generation of stars,” says astronomer Roberto Maiolino of the University of Cambridge, co-author of the studies. “There are no other really satisfactory explanations for other types of sources.”
The team estimates that Hebe is up to 1,200 light years across, with two distinct clusters, and contains the mass between 10,000 and several hundred thousand suns. But because first-generation stars are massive, the cluster could contain only a few hundred stars.
Hebe was also discovered near a galaxy, named GN-z11, with a mass of 1 billion suns. Some computer simulations suggest that population III stars should not be found near such galaxies, which have evolved chemically and therefore polluted their environment with heavy elements. According to Fujimoto, Hebe’s proximity to GN-z11 “opens new questions about how such systems form and survive.”
Other simulations suggest that the gravity of these galaxies could attract pockets of pristine gas from their surroundings, creating the conditions necessary for the formation of Population III stars. Hebe’s discovery, along with future studies of Population III candidates, will help astronomers better understand the birthplaces of these pristine stars, Maiolino says.
