The star exploded when the Universe was just 2 billion years old — Webb detected its light

The James Webb Space Telescope has helped astronomers study one of the most distant supernovae known. The light from SN 2023aeaf has been travelling towards Earth for around 11.7 billion years, whilst the star itself exploded at a time when the Universe was approximately 2 billion years old.

Observations indicate that, with 97.2 per cent probability, this is a Type II supernova — the result of the collapse of the core of a massive star that retained its hydrogen envelope. However, the type of event has been determined on the basis of photometry and modelling, rather than being confirmed by characteristic lines in the spectrum of the supernova itself.

Details

SN 2023aeaf was discovered as part of the COSMOS-Web survey. Spectroscopy of the host galaxy has allowed the redshift z = 3.195 to be reliably determined. This places the event in the early Universe, when galaxies were younger and, on average, contained fewer heavy elements.

Based on the light curve and colour shift, the researchers concluded that a Type II supernova is the most likely explanation. Simulations using the STELLA code best describe the explosion of a star with an initial mass of around 12 solar masses, although a wider range of parameters is possible due to the small number of observations.

The early radiation proved particularly unusual: the supernova was very hot and blue. One possible explanation is that the shock wave following the explosion collided with dense material that the star had managed to eject shortly before its demise. The best model suggests that there was about 0.5 solar masses of such circumstellar material.

The galaxy in which the explosion occurred is relatively small, actively forming new stars and poor in heavy elements. It is precisely these conditions that allow us to test whether the deaths of massive stars in the early Universe differed from the processes that astronomers observe nearby today.

Why this is important

Most supernovae that have been studied in detail occurred much closer to Earth and in a chemically more mature Universe. SN 2023aeaf offers a rare opportunity to witness the death of a massive star under conditions characteristic of a much earlier cosmic era.

If future observations confirm that distant supernovae interacted more frequently with the dense matter surrounding their stars, this will help us better understand the evolution of massive stars and the rate of star formation at different stages in the history of the Universe.

However, the sample of supernovae at a redshift of 3 remains small. The authors emphasise that new objects and more extensive observation campaigns are needed to distinguish general patterns in the early Universe from the specific characteristics of a single star.

Source

Study: “Analysis of a Type II Supernova Candidate at z = 3.19 from JWST’s COSMOS-Web Survey”. Authors: Valeria Aparicio et al. The Astrophysical Journal, 2026, Volume 1007, Issue 2, Article 133. Published 20 August 2026.