How did Koshiba detect neutrinos from supernovae?
On February 23, 1987, our Kamiokande detector recorded a burst of 11 neutrinos from Supernova 1987A, a stellar explosion in the Large Magellanic Cloud. These neutrinos arrived about three hours before the optical light, confirming that neutrinos escape the collapsing core almost instantly. We detected them via the Cherenkov radiation emitted when a neutrino interacts with water, producing a charged particle that moves faster than light in the medium. The timing and energy of these events matched theoretical predictions for core-collapse supernovae. This was a triumph of patience and precision: we had built the detector to study proton decay, but serendipity gave us a front-row seat to a cosmic event. Every neutrino carried a message from the heart of that dying star, and we were privileged to listen.
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