Light needs time to travel. From distant galaxies, it takes billions of years to reach us. To look far away is to look into the past.
It’s not about watching a recording of the ancient universe. The photons left those objects when they were young and have traveled through space ever since. Each distant point that we capture offers, therefore, an image of a different era. For this reason, telescopes not only allow us to explore enormous distances: they also allow us to reconstruct chapters of cosmic history.
And the James Webb telescope has detected a flash called AT 2026abck, emitted when the universe was about 1.15 billion years old. It could be a supernova, the explosion of a star. Scientists estimate that they observed it only between four and ten days after the explosion, depending on the time of that galaxy.
This does not mean that we detected it a few days after it happened according to our calendar. The signal began its journey more than 12 billion years ago. The calculation refers to the phase in which the phenomenon was when emitting the radiation that we now receive. To study its nature, astronomers compare observations taken at different times and look for how its brightness changes. They also analyze the colors of light, which contain information about the source.
And there is another surprise: due to the expansion of the universe, from here, the explosion would seem to develop six times more slowly.
As it traveled, cosmic expansion stretched its light waves to longer wavelengths. This same stretch affects the intervals between successive signals, so that remote events appear to occur in slow motion. It’s not that time worked differently in that galaxy: it’s about how we receive light.
It is not yet confirmed that it is a supernova, but it offers clues about the death of primitive stars.
REFERENCES
Ming-Yang Zhuang, Yue Shen, Lei Hu, Justin DR Pierel, Zhiwei Pan, Zachary Stone, Adam J. Burgasser, Xiaohui Fan, Jenny E. Greene, Junyao Li and Feige Wang. “NEXUS: Discovery of a Luminous Young Transient at z = 5.” arXivSeptember 29, 2026.
Ryan MT White, Tamara M. Davis, Geraint F. Lewis et al. “The Dark Energy Survey Supernova Program: slow supernovae show cosmological time dilation out to z ∼ 1”. Monthly Notices of the Royal Astronomical SocietyAugust 21, 2024.
