Physicists in Japan found a stable excess of neutrino events in nearly 5,000 days of data from the Super-Kamiokande detector, reaching 99.5% confidence. This matches the diffuse supernova neutrino background, a faint glow from billions of past supernovae.

Super-Kamiokande uses 50,000 tons of ultra-pure water and about 13,000 light sensors buried a kilometer underground to catch rare neutrino interactions.

Confirming this signal would open a new way to observe black hole and neutron star births from ancient supernovae. Final confirmation will come with the next-generation Hyper-Kamiokande detector.