Some cosmic records fall by a little. This one fell by more than a billion years. The James Webb Space Telescope has confirmed a supernova that exploded when the universe was just 730 million years old, the earliest stellar death ever observed. The flash began as a gamma-ray burst detected in March 2025, and Webb's follow-up observations showed it was a collapsing massive star, not some other kind of cosmic flare.

The story starts with GRB 250314A, a gamma-ray burst picked up in mid-2025 by the Space Variable Objects Monitor, a small X-ray telescope developed by China and France. Gamma-ray bursts are the brightest explosions in the universe, but they can come from more than one cause. The crucial step was Webb's near-infrared imaging in July 2025, which captured the fading light and its spectrum in enough detail to identify it.

The spectrum matched a core-collapse supernova: a massive star running out of fuel, its core imploding, and its outer layers being blown into space. That identification matters because it turns a mysterious flash into a known physical event, and it pushes the confirmed record for such explosions far earlier than Webb's previous record, a supernova from about 1.8 billion years after the Big Bang.