1987A

1987A refers to Supernova 1987A, a core-collapse supernova that occurred in the Large Magellanic Cloud in February 1987. It was the closest observed supernova since Kepler's 1604, allowing detailed study across the electromagnetic spectrum and in neutrinos. The explosion date is placed at February 23, 1987, with the progenitor identified as Sanduleak -69 202, a blue supergiant of spectral type B3 I, about 20 solar masses. The progenitor's evolution to a blue supergiant prior to explosion challenged standard models of massive-star death, which often assumed red supergiants for Type II supernovae.

SN 1987A is classified as a peculiar Type II supernova (II-pec) because of its unusual light curve, which rose more slowly to maximum over about 80 days, and its blue supergiant progenitor. A burst of neutrinos was detected by several detectors (Kamiokande II in Japan, IMB in the United States, and Baksan in Russia) beginning within hours of the collapse, confirming core-collapse theory and marking one of the first direct astrophysical neutrino observations.

Hubble Space Telescope and ground-based observations revealed a distinctive triple-ring nebula around the supernova, interpreted as a pre-existing circumstellar medium shaped by the progenitor’s mass loss. The equatorial ring and two fainter outer rings became more luminous as the fast ejecta from the explosion collided with the rings during the 1990s and 2000s. The event provided valuable data on nucleosynthesis, with detection of 56Co decay gamma rays, and on the early evolution of supernova remnants.

Today the remnant continues to be studied across wavelengths (radio, optical, infrared, X-ray), with ongoing interaction between ejecta and circumstellar material. A compact remnant is expected to be a neutron star, but as of the latest observations no definitive detection has been confirmed.