Astronomers have discovered a supernova so distant that it dates back to a time when the cosmos was still very young, thus providing an unprecedented look at the first stars.
Thanks to the James Webb Space Telescope, an international team was able to identify this stellar explosion, linked to a gamma-ray burst detected in March 2025. This event, which occurred approximately 13 billion years ago, is situated in the Epoch of Reionization, an important phase of galaxy formation.
Artist's impression of one of the brightest explosions ever seen, called a Luminous Fast Blue Optical Transient (LFBOT). It shines intensely in blue and evolves rapidly, reaching its peak brightness within days.
Credit: NASA, ESA, NSF's NOIRLab, Mark Garlick, Mahdi Zamani
This supernova offers a unique window into the first generations of stars. Indeed, during the Epoch of Reionization, conditions such as low metallicity could influence the end of life of massive stars. Yet, this discovery reveals surprising similarities with more recent explosions.
Observations made with JWST's near-infrared camera, about 110 days after the gamma-ray burst, allowed the supernova's glow to be separated from that of its host galaxy. This technique confirmed the presence of the explosion at an extreme distance, as detailed in Astronomy & Astrophysics.
Interestingly, this ancient supernova presents luminosity and spectral characteristics comparable to SN 1998bw, a local explosion associated with a gamma-ray burst. This resemblance indicates that massive stars in the early Universe were not radically different, despite an environment less rich in heavy elements.
Consequently, this observation leads us to reconsider stellar evolution in the young Universe. It constitutes a valuable reference point, showing that explosions could be similar to those observed today, which opens the way to new questions about the uniformity of cosmic phenomena.
Also, the team plans new observations with JWST in a year or two, once the supernova's light has faded. This approach will allow for better characterization of the host galaxy.
Gamma-ray bursts and their link to supernovae
Gamma-ray bursts are brief, intense emissions of gamma rays, the most energetic in the electromagnetic spectrum. They often originate from the collapse of massive stars at the end of their lives, triggering colossal explosions. These events can last from a few milliseconds to several minutes, and they are detected by specialized satellites.
When a gamma-ray burst is associated with a supernova, it signals the violent death of a giant star. The resulting supernova releases an immense amount of energy and chemical elements, enriching the surrounding space. This connection is important for understanding how massive stars influence galaxy formation and the distribution of matter.
Astronomers use these associations to study the properties of stars at different epochs. By comparing local gamma-ray bursts to those from the young Universe, they can deduce whether the explosion mechanisms have changed. The recent finding with JWST shows that these processes appear similar despite billions of years of separation, providing clues about the constancy of physical laws.