NASA’s James Webb Space Telescope may have caught a stellar explosion in the early universe only days after it occurred, offering astronomers a rare look at a possible supernova from a time when the cosmos was still young.
The transient, designated AT 2026abck, was found in a star-forming galaxy at a redshift of 5.017. The observations suggest Webb saw the event roughly four to 10 days after the explosion. A paper describing the finding was posted to the arXiv preprint server on September 29, so the result remains preliminary.
A difficult cosmic target
Supernovae at great distances are challenging to study because their light is stretched into infrared wavelengths as the universe expands. Webb’s infrared instruments are designed for this regime, enabling surveys to search for transient events in galaxies at redshifts reaching about 6.
Researchers have identified more than 200 potential supernova events with host-galaxy redshifts out to around 6. Yet the most distant candidates are often observed only once or a few times, making it difficult to establish their nature and evolutionary stage. Capturing one close to its explosion is especially uncommon.
Beyond redshift 5, only one supernova has been confirmed spectroscopically, according to the report, and that event benefited from substantial gravitational magnification by a galaxy cluster. AT 2026abck is notable because its field is not lensed or magnified by a galaxy or cluster.
Found through repeated observations
The candidate emerged from NEXUS, a Webb Treasury program that returns to the same region of sky approximately every two months. On May 28, 2026, the reported location showed no corresponding source. Later observations revealed the transient.
That repeat-survey approach is crucial for detecting rapidly changing objects. A single deep image can reveal distant galaxies, but multiple visits allow astronomers to distinguish a new transient source from the stable background of distant galaxies.
The reported redshift places the host galaxy at an era when galaxies were younger, actively forming stars and generally more metal-poor than many nearby systems. Supernovae in such environments can help researchers investigate how massive stars lived and died under conditions unlike those in the modern universe.
What confirmation would mean
AT 2026abck is described as a possible supernova, not a confirmed one. Establishing its classification will depend on continued analysis and follow-up observations. Its early detection nevertheless demonstrates the kind of time-domain astronomy Webb can support when it repeatedly observes deep extragalactic fields.
If confirmed, the event would add evidence that unlensed, very distant supernovae can be discovered early enough to study their evolution. Such observations could also contribute to measurements of the cosmic history of star formation, because supernova rates provide an independent indication of how often massive stars formed and ended their lives.
The candidate does not by itself settle broader questions about early stellar populations. But it illustrates how Webb’s infrared sensitivity and repeated survey observations are beginning to open a more direct window onto transient phenomena in the young universe.
A promising early signal
For now, the result should be viewed as an intriguing preprint-based detection rather than a final classification. The strongest significance lies in its timing and distance: a possible stellar death seen within days of eruption in a galaxy at redshift 5.017, without the observational boost of gravitational lensing.
As programs such as NEXUS build additional epochs of observation, astronomers will have more opportunities to find and characterize distant explosions. Each well-observed event can help turn isolated discoveries into a clearer picture of how stars and galaxies evolved in the universe’s earlier chapters.
This article is based on reporting by Phys.org. Read the original article.
Originally published on phys.org
