SN 1987A: neutrinos from a collapsing core reach Earth

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Three underground detectors - Kamiokande-II in Japan, IMB in Ohio and Baksan in the Soviet Union - recorded a coincident burst of neutrino interactions lasting about a dozen seconds, totalling roughly two dozen events. The optical supernova was found in the Large Magellanic Cloud, about 50 kiloparsecs away, the following night. It remains the only occasion on which the collapse of a stellar core has been observed by any means other than the light it eventually produced, and the neutrino timing and energies matched core-collapse predictions closely enough to confirm the mechanism. The progenitor, catalogued as Sanduleak -69 202, was a blue supergiant rather than the red supergiant theory expected - a genuine surprise that forced revisions to massive-star evolution models. Event counts are quoted inconsistently in the literature, with Kamiokande-II's given as both 11 and 12.

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