Signal from a Supernova: Neutrinos Captured ✦

The explosion of a massive star, shrouded in dense gas and dust, is like a locked room. Only ghostly couriers—neutrinos—can slip out, carrying news of the catastrophe. Catching these couriers requires a trap of planetary scale: the IceCube detector is a cubic kilometer of Antarctic ice threaded with sensors. In six days, it registered four neutrinos flying from a single point—exactly where the supernova SN 2021foa flared up.

The total energy of these particles exceeded the star’s entire light output by hundreds of times. A simple collision of the ejected material with surrounding gas and dust can't provide such acceleration. Inside, an invisible engine likely kicked in—a newborn black hole or neutron star, producing a powerful jet. The jet didn't punch through the shell, but accelerated particles to the limit, causing a neutrino shower. This picture was first sketched back in the last century by Fritz Zwicky and Subrahmanyan Chandrasekhar. The star itself was also surprising: its light switched several times between hydrogen and helium type, for which astronomers nicknamed it the 'quick-change' supernova.

Thus, neutrinos for the first time allowed us to peer into the heart of the explosion, hidden from ordinary telescopes. This ghostly mail will reveal the active cores of distant galaxies and the supermassive black holes at their centers. Future detectors, like KM3NeT, and precise photometry will help compose the full picture.