The James Webb Space Telescope has confirmed the source of an extraordinarily distant flash of light: a supernova from a massive star that exploded when the Universe was a mere 730 million years old. This event, detected as a gamma-ray burst in March 2025, is now the earliest supernova ever observed, shattering Webb’s own previous record.
“Only Webb could directly show that this light is from a supernova – a collapsing massive star,” said lead researcher Andrew Levan. “This demonstrates we can use Webb to find individual stars when the Universe was only 5% of its current age.”
The discovery began with an alert from the Franco-Chinese SVOM satellite. Ground and space telescopes worldwide swiftly pinpointed the burst’s location and estimated its vast distance. Webb’s critical role was to provide rapid, sensitive follow-up observations months later, precisely when the underlying supernova was predicted to be brightest.
The findings held a major surprise. Despite exploding in the primitive, early Universe—where the first stars were theorized to be fundamentally different—this supernova looks strikingly similar to modern, nearby supernovae. “We went in with open minds,” said co-author Nial Tanvir. “And lo and behold, Webb showed that this supernova looks exactly like modern supernovae.”
For the first time in such a remote event, Webb also detected the supernova’s host galaxy, though it appears only as a faint, reddened smudge. “Webb’s observations indicate that this distant galaxy is similar to other galaxies that existed at the same time,” noted astronomer Emeric Le Floc’h.
The research opens a new window into the cosmic dawn. The team plans to use Webb to study more of these rare, ancient gamma-ray bursts. By analyzing their afterglow, they hope to get a detailed “fingerprint” of the early galaxies that hosted these cataclysmic stellar deaths, further illuminating the Universe’s first chapters.
