Neutrino Astrophysics

Supernova 1987A: first supernova observed in neutrinos

Very large stars can end their lives in a cataclysmic explosion called a supernova. The photographs show a supernova in the Large Magellanic Cloud, a satellite galaxy of the Milky Way located only about 160,000 light years away. Photographed in 1987, and named 1987A, it was the first supernova visible to the naked eye since early in the seventeenth century. In fact, at its brightest, a typical supernova outshines all the other stars combined in its galaxy.

Astrophysicists have predicted that a supernova explosion would produce a sharp pulse of neutrinos, the elusive uncharged particles that move at or near the speed of light. Neutrinos interact with matter hardly at all and are therefore extremely difficult to detect. In 1987 two big detectors were up and running, part of the field of experimental neutrino physics, and they observed neutrinos from supernova 1987A.

Neutrinos carry nearly all of the energy of a supernova explosion. After the explosion of 1987A, the two detectors observed an increase of 19 neutrino counts, the first ever observation of neutrinos produced by a supernova. Moreover, the neutrinos arrived in a pulse about three hours before the visible light from the supernova, just as astrophysicists had predicted.

Supernova 1987A (left) Star field before explosion (right) Copyright Anglo-Australian Observatory. Photograph by David Malin.