Astronomers using the James Webb Space Telescope have identified one of the most distant exploding stars ever confirmed. The supernova, SN 2023aeaf, was found at a redshift of 3.195—so far away that its light has been traveling for roughly 11.7 billion years. The study, published in The Astrophysical Journal on Aug. 13, offers a close-up look at how massive stars die in the young universe’s primitive, metal-poor conditions.
Exploding oldies
Massive stars exploding in a core-collapse supernova explosion can be used as tracers for actively forming stars and the physical consequences their explosive deaths exert on the surrounding gas cloud. These explosions actively reshape the environment and set the stage for the next generation of stars to form. Their rate of occurrence tells astronomers indirectly about how vigorously stars were forming throughout the universe’s history.
But almost everything astronomers know about how these explosions actually behave comes from nearby, relatively recent examples. Because the early universe had very low metal content, a major question persists over whether these explosions behaved differently far back in the early universe. Testing this requires finding and studying distant supernova candidates, which are extremely faint and therefore hard to detect.
Thanks to its exceptional sensitivity, the James Webb Space Telescope (JWST) has expanded the sample of these ultra-distant explosions through deep imaging surveys such as JADES and COSMOS-Web. In this study, astronomers report one such supernova, SN 2023aeaf, found in the COSMOS-Web survey. Spectroscopic analysis has confirmed its redshift of z = 3.195, corresponding to a time when the universe was only about 2 billion years old.
Metal-poor home
In this work, Valeria Aparicio of the Institute for Astronomy at the University of Hawai’i and colleagues analyze this explosion to determine its classification and the properties of its host galaxy.
Using careful comparisons of its brightness pattern over time, called the light curve, and color evolution with simulated populations of supernovae, the team classified it as a Type II supernova. This type of explosion occurs when a massive star exhausts its nuclear fuel and its iron core collapses under its own gravity. The spectrum is marked by hydrogen lines, as the star still has its hydrogen-rich outer envelope intact when it dies. The team found this classification had a probability of 97.2%.
The team also studied the spectrum of the supernova’s host galaxy. They determined that it is a young, actively star-forming dwarf galaxy with a relatively low proportion of heavier elements. “The low-mass, metal-poor host environment of SN 2023aeaf is also consistent with expectations for massive-star explosions in chemically young galaxies at z ∼ 3,” the team writes in the paper.
Hot beginnings
Using specialized simulation software called STELLA, researchers modeled the explosion and found that, early on, the supernova was unusually hot and blue. This could best be explained by its blast wave slamming into a compact shell of gas that the star had shed shortly before dying. It later cooled to a temperature matching the well-known “plateau phase” typical of this supernova type after the early interaction faded.
Researchers say that although the data are limited, they are most consistent with a progenitor star roughly 12 times the sun’s mass, surrounded by about half a solar mass of circumstellar material. Because they had only a couple of observations spread over time, the researchers couldn’t pin down detailed properties of the exploding star with much precision.
This discovery adds to the small but growing sample of supernovae found beyond redshift 3. The team calls for a larger sample of similar objects to properly describe this population of distant supernovae. As the sample grows, the rate of these occurrences could help pin down the cosmic star formation history.
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Publication details
Valeria Aparicio et al, Analysis of a Type II Supernova Candidate at z = 3.19 from JWST’s COSMOS-Web Survey, The Astrophysical Journal (2026). DOI: 10.3847/1538-4357/ae884f
Key concepts
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JWST reveals likely Type II supernova from when universe was only 2 billion years old (2026, August 31)
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