Supernova at edge of observable universe spotted by James Webb Space Telescope

by Robert Schreiber
Berlin, Germany (SPX) Dec 17, 2025
An international collaboration of astronomers has used the James Webb Space Telescope (JWST) to detect a supernova at an unprecedented distance in the early universe, tied to a long-duration gamma-ray burst. The team observed the explosive death of a massive star when the universe was about 730 million years old, placing the event deep in the era of reionisation. The discovery offers a direct view of the final stages of a massive star at a time when the first generations of stars and galaxies were emerging.

The explosion, designated SN in GRB 250314A, was first identified on March 14, 2025 as a bright burst of high-energy radiation detected by the space-based multi-band astronomical Variable Objects Monitor (SVOM). Follow-up spectroscopy with the European Southern Observatory's Very Large Telescope (ESO/VLT) confirmed the gamma-ray burst originated at a redshift of about 7.3, corresponding to the very early universe.

The critical evidence for the supernova came from targeted observations with JWST's Near-Infrared Camera (NIRCam) about 110 days after the initial burst. At that time, researchers were able to disentangle the light from the fading explosion and the much fainter underlying host galaxy, isolating the supernova's contribution.

Co-author and UCD School of Physics astrophysicist Dr Antonio Martin-Carrillo said: "The key observation, or smoking gun, that connects the death of massive stars with gamma-ray bursts is the discovery of a supernova emerging at the same sky location. Almost every supernova ever studied has been relatively nearby to us, with just a handful of exceptions to date. When we confirmed the age of this one, we saw a unique opportunity to probe how the Universe was there and what type of stars existed and died back then.

"Using models based on the population of supernovae associated with GRBs in our local universe, we made some predictions of what the emission should be and used it to proposed a new observation with the James Webb Space Telescope. To our surprise, our model worked remarkably well and the observed supernova seems to match really well the death of stars that we see regularly. We were also able to get a glimpse of the galaxy that hosted this dying star."

Photometric and spectral analysis show that the distant supernova's brightness and spectral characteristics are closely aligned with those of the prototype gamma-ray-burst-associated supernova SN 1998bw in the nearby universe. This match indicates that the massive star that collapsed to produce GRB 250314A and its supernova was not markedly different from progenitor stars seen in the local cosmos, even though it formed under the lower metallicity conditions expected in the early universe. The team also ruled out a more luminous class of explosions, such as a superluminous supernova, for this event.

These results challenge expectations that stars in the early universe, formed in extremely metal-poor environments, would produce supernovae that differ strongly in luminosity or colour from those observed today. Instead, the observations suggest a surprising continuity in the core-collapse processes powering gamma-ray-burst-associated supernovae across more than 13 billion years of cosmic history. The finding provides a key anchor point for models of stellar evolution and death during the reionisation era.

The researchers plan to obtain a second epoch of JWST observations within the next one to two years, once the supernova has faded by more than two magnitudes. Those deeper observations will allow them to characterise the faint host galaxy in detail and firmly separate the residual galaxy light from any remaining supernova emission. The extended dataset will refine measurements of the host's properties and further test how typical this early-universe stellar explosion is compared with local counterparts.

Research Report:JWST reveals a supernova following a gamma-ray burst at z ~7.3