When the James Webb Space Telescope speak, astronomers listen. This time, however, the telescope did much more: it brought to light the oldest supernova ever observedan explosion that occurred when the universe was still learning to exist.
His light – gone 730 million years after the Big Bang – has reached us after a very long journey, allowing us to see a galaxy so distant that it appears only as a small red dot among hundreds of others.
For years it was thought that the first stars were strange, almost unrecognizable compared to current ones: enormous, unstable, composed only of very light elements. This supernova, however, behaves like the stellar explosions we observe today. A similarity that is pushing scientists to review many models of stellar evolution.
A ten second flash
The story begins on March 14, 2025when the telescope SVOM recorded a very brief flash: a gamma-ray burstwhich lasted just ten seconds. It’s the type of event that doesn’t allow repeats: if you don’t see it right away, it disappears forever.
From that moment on, a global collaboration began. The Swift Observatory identified the exact origin of the flash, the Nordic Optical Telescope showed a faint infrared glow, an unambiguous signal of the distance and the Very Large Telescope of ESO has set the age of the event: a very young universe, still in transformation.
Astronomers knew that, due to the expansion of space, the light from the supernova would take months to become visible. As, on July 1stthe James Webb pointed his instruments towards that area. And there it was: the supernova, cataloged as GRB 250314Aalong with its host galaxy, barely perceptible but present.
With this observation, Webb also surpassed his previous record: a supernova “only” 1.8 billion years old. This result shows that the telescope can recognize individual stars that exploded when the cosmos was just 5% of its current age. A huge leap forward, which allows us to study eras that were almost out of reach until now.
Scientists now want to exploit gamma-ray bursts as “light signals” to find other primordial galaxies. Their afterglow could become a useful fingerprint for understanding what the universe was really like in its early stages. It’s a bit like shining a torch in a room we thought was dark: we don’t see everything, but we finally have a place to start.
