Supernova 1987a

Supernova 1987a was a supernova in the Large Magellanic Cloud, a nearby dwarf galaxy. It occurred approximately 50 kiloparsecs from Earth, the closest supernova since Supernova 1604, which occurred in the Milky Way itself. The light from the supernova reached Earth on February 23, 1987. Its brightness peaked in May with a magnitude of about 3 and slowly declined in the following months. It was modern astronomers' first opportunity to see a supernova up close.

Since 50 kiloparsecs is 164,000 light-years the cosmic event itself happened ca. 164,000 years ago.

Approximately three hours before the visible light from SN 1987a reached the Earth, a burst of neutrinos was observed at two separate neutrino observatories[?], which had originally been built to study the solar neutrino problem. Although the actual neutrino count was small - less than twenty in all - it was a significant rise from the previously-observed background level. This was the first time neutrinos emitted from a supernova had been directly observed, and this detection was consistent with theoretical supernova models, in which most of the energy of the collapse is radiated away in neutrinos.

Most astrophysicists and particle physicists regret two neutrino experiments that were not done. First of all, if the star had been ten light years further and therefore been observed ten years later, the neutrino burst would have been detected by much more sensitive neutrino detectors that would have been able to measure the energy spectra of the neutrinos. Second, if the two neutrino observatories were on two sides of the earth and had their clocks been synchronized, it would have been possible to measure the time needed for the burst to travel between the detectors, and it would have been possible to determine if the neutrinos were travelling at the speed of light like a massless particle or less than the speed of light like a massive particle. Unfortunately, while one of the labs had their detector synchronized to an atomic clock, the other lab did not see the need to record the exact moment of neutrino detection, and this experiment was impossible.

The precursor to SN 1987a was a blue supergiant. This required some revisions to models of high mass stellar evolution which suggested that supernova would result from red supergiants.

The supernova remnant formed by debris from SN 1987a is one of the most-studied astronomical objects today.

External Link

• Picture of Supernova 1987a (http://antwrp.gsfc.nasa.gov/apod/ap970124)