The James Webb Space Telescope has detected supernova SN 2023aeaf at redshift z = 3.195 — one of the highest spectroscopically confirmed values for a supernova. Light from this explosion traveled to us for over 11.5 billion years, meaning the star exploded when the Universe was only about 2 billion years old.
The discovery was made as part of the COSMOS-Web survey. Two JWST images taken ~1 month apart in the supernova's rest frame allowed classification as a Type II supernova — a massive star's core collapse. Comparison with models suggests the most likely progenitor was a star of ~12 solar masses surrounded by ~0.5 solar masses of circumstellar material.
A spectrum was also obtained ~30 rest-frame days after discovery, but it shows no clear supernova features — hydrogen emission (Hα) from the host galaxy likely masks the signal from the explosion itself.
The host galaxy is star-forming, with low metallicity and a stellar mass of about one billion solar masses. This fits an emerging pattern: early-Universe core-collapse supernovae tend to occur in bright, metal-poor environments with dense circumstellar shells.
SN 2023aeaf joins a small but growing sample of early-Universe supernovae that JWST is discovering one by one — each offering new clues about how massive stars lived and died in the young cosmos.