Astronomers using the James Webb Space Telescope have detected the light from a massive star that exploded about a billion years after the universe's birth. This type II supernova, named SN Eos, offers insights into the early stellar populations during the cosmic dark ages. The finding marks the earliest such event confirmed through spectroscopy.
The James Webb Space Telescope has enabled the observation of SN Eos, a type II supernova that occurred when the universe was just one billion years old. This explosion came from a massive star that depleted its fuel, producing a burst of light now reaching Earth after billions of years.
David Coulter at Johns Hopkins University in Baltimore, Maryland, and his team identified the supernova, which was positioned behind a massive galaxy cluster. The cluster's gravity acted as a lens, amplifying the light by tens of times and allowing detailed study. Analysis of the light spectrum confirmed it as a type II supernova, the first such detection at this distance using spectroscopy.
The star responsible had unusually low levels of elements heavier than hydrogen and helium—less than 10 percent of those in the sun. This composition aligns with expectations for the early universe, where few generations of stars had yet formed to enrich the cosmos with heavier elements.
"That tells us immediately about what kind of stellar population [the star] exploded in," says Or Graur at the University of Portsmouth, UK. "High-mass stars explode very, very quickly after birth. In cosmological terms, a million years or so, that's nothing. So they tell you about the ongoing star formation in that galaxy."
The event occurred shortly after the epoch of reionisation, when light from the first stars ionised neutral hydrogen, making the universe transparent to radiation. "This is very, very close to that period of reionisation when the universe exited its short, dark period and photons could stream freely again and we could see things," Graur adds.
Matt Nicholl at Queen's University Belfast, UK, highlights the significance: "We can see this individual star, with beautiful data, at a [distance] where we've never seen an isolated supernova, and the data are good enough to see that the stars are different from most of the stars in the local universe."
This discovery provides a rare glimpse into the death of early massive stars, revealing properties of galaxies in the universe's infancy. The research is detailed in arXiv:2601.04156.