An international team of astronomers has, for the first time, successfully probed the early universe.
An international group of astronomers has reached a new milestone in studying the early universe. Using the James Webb Space Telescope (JWST), the team identified a supernova, the catastrophic explosion that marks the death of a massive star, at a distance never before observed.
The explosion, known as SN in GRB 250314A, occurred when the universe was only about 730 million years old. This places it firmly within the era of reionisation, a formative period when the first generations of stars and galaxies were emerging. Observing such an event offers a rare window into how massive stars ended their lives during the universe’s earliest stages.
Details of the discovery are described in a study recently published in the journal Astronomy & Astrophysics. The event was first noticed as an intense flash of high energy light, called a long-duration Gamma-Ray Burst (GRB), detected on March 14, 2025 by the space-based, multi-band astronomical Variable Objects Monitor (SVOM). Subsequent observations with the European Southern Observatory’s Very Large Telescope (ESO/VLT) confirmed that the source lay at an extreme cosmic distance.
JWST Observations Reveal the Supernova
The key finding came from focused observations made with JWST’s Near-Infrared Camera (NIRCAM) roughly 110 days after the initial burst. These measurements allowed researchers to distinguish the fading glow of the supernova from the much fainter light of its host galaxy, confirming the presence of the stellar explosion far back in cosmic history.
Co-author and astrophysicist at UCD School of Physics, 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 propose 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.”
A Familiar Explosion in an Unfamiliar Universe
The data indicate that the distant supernova is surprisingly similar in brightness and spectral properties to the prototype GRB-associated supernova, SN 1998bw, which exploded in the local universe.
This similarity suggests that the massive star that collapsed to create GRB 250314A was not significantly different from the progenitors of GRBs observed locally, despite the vastly different physical conditions (such as lower metallicity) in the early universe. The observations also ruled out a much more luminous event, such as a Superluminous Supernova (SLSN).
The findings challenge the assumption that the stars of the early universe, formed under extremely low-metallicity conditions, would lead to markedly different, perhaps brighter or bluer, stellar explosions than those seen today.
While this discovery provides a powerful anchor point for understanding stellar evolution in the early universe, it also opens new questions about the observed uniformity.
The research team plans to secure a second epoch of JWST observations in the next one to two years. By that time, the supernova light is expected to have faded significantly (by over two magnitudes), allowing the team to completely characterize the properties of the faint host galaxy and confirm the supernova’s contribution.
Reference: “JWST reveals a supernova following a gamma-ray burst at z ≃ 7.3” by A. J. Levan, B. Schneider, E. Le Floc’h, G. Brammer, N. R. Tanvir, D. B. Malesani, A. Martin-Carrillo, A. Rossi, A. Saccardi, A. Sneppen, S. D. Vergani, J. An, J.-L. Atteia, F. E. Bauer, V. Buat, S. Campana, A. Chrimes, G. Corcoran, B. Cordier, L. Cotter, F. Daigne, V. D’Elia, M. De Pasquale, A. de Ugarte Postigo, R. A. J. Eyles-Ferris, H. Fausey, A. S. Fruchter, O. Godet, B. P. Gompertz, D. Götz, N. Habeeb, D. H. Hartmann, L. Izzo, P. Jakobsson, T. Laskar, A. Melandri, P. T. O’Brien, J. T. Palmerio, L. Piro, G. Pugliese, Y. L. Qiu, B. C. Rayson, R. Salvaterra, S. Schanne, A. L. Thakur, C. C. Thöne, D. Watson, J. Y. Wei, K. Wiersema, R. A. M. J. Wijers, L. P. Xin, D. Xu and S. N. Zhang, 9 December 2025, Astronomy & Astrophysics.
DOI: 10.1051/0004-6361/202556581
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