JWST reveals likely Type II supernova from when universe was only 2 billion years old

Astronomers using the James Webb Space Telescope have identified one of the most distant exploding stars ever confirmed, SN 2023aeaf, which 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. The team classified it as a Type II supernova, which occurs when a massive star exhausts its nuclear fuel and its iron core collapses under its own gravity. The team found this classification had a probability of 97.2%. The supernova's host galaxy is a young, actively star-forming dwarf galaxy with a relatively low proportion of heavier elements.

The team used specialized simulation software called STELLA to model 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. The 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.

• SN 2023aeaf was found in the COSMOS-Web survey.
• It has a redshift of z = 3.195, corresponding to a time when the universe was only about 2 billion years old.
• The host galaxy is a young, actively star-forming dwarf galaxy with a relatively low proportion of heavier elements.

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