Supernova 1987a

Helping orphans the way you would do it

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. As the first supernova discovered in 1987, it was labeled "1987a." Its brightness peaked in May with a apparent 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 approximately 164,000 light-years, the cosmic event itself happened approximately 164,000 years ago.

1987a supernova remnant near the center

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 - fewer 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 observed directly, and the observations were consistent with theoretical supernova models in which most of the energy of the collapse is radiated away in neutrinos.

It is a source of regret to astrophysicists and particle physicists that two particular experiments were not done. First of all, the energy spectra of the neutrinos could have been measured if more sensitive neutrino detectors had been available. Secondly, if the clocks of two neutrino observatories had been synchronised, it would have been possible to measure the time the burst took to travel between them, and thus to determine whether the neutrinos were travelling at the speed of light (like massless particles) or slower than the speed of light (like massive particles). Unfortunately, while the detector in one of the laboratories was synchronized to an atomic clock, the detector in the other laboratory was not, and this experiment was impossible.

One highly significant result was obtained from the data however. It appears that the neutrinos and antineutrinos both took the same time to arrive at earth, about 164,000 years, and from general relativity one would expect gravity to increase the travel time by about five months. The difference in their arrival times was less than 12 seconds. This is the first empirical evidence that matter and antimatter react similarly to gravitational fields, which was widely predicted but not previously tested directly.

The precursor to SN 1987a was a blue supergiant presumed to have a mass of about 20 solar masses. This required some revisions to models of high mass stellar evolution, which had suggested that supernovae would result from red supergiants.

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

Supernova 1987a

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