SN 1987A
Encyclopedia : S : SN : SN1 : SN 1987A
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| The closest recorded sn. since invention of telescope |} SN 1987A was a supernova in the outskirts of the Tarantula Nebula in the Large Magellanic Cloud, a nearby dwarf galaxy. It occurred approximately 51.4 kiloparsecs from Earth [link], the closest supernova since SN 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 51.4 kiloparsecs is approximately 168,000 light-years, the cosmic event itself happened approximately 168,000 years ago. To put this in perspective, Homo sapiens (modern humans) evolved about 200,000 years ago.
Neutrino emissions
Approximately three hours before the visible light from SN 1987A reached the Earth, a burst of neutrinos was observed at three separate neutrino observatories (Kamiokande II, IMB and Baksan). It is widely thought that this is due to the neutrino emission preceding the emission of visible light, and that the neutrinos did not actually outrace the light. At 7:35am Universal time, Kamiokande II detected 11 neutrinos, IMB 8 neutrinos and Baksan 5 neutrinos, in a burst lasting less than 13 seconds. Although the actual neutrino count was only 24, 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 99% of the energy of the collapse is radiated away in neutrinos. The observations are also consistent with the models' estimates of a total neutrino count of [10^] with a total energy of [10^] joules. One highly significant result was obtained from the data regarding gravity. It appeared that the neutrinos and antineutrinos both took the same time to arrive at earth, about 168,000 years. The difference in their arrival times was less than 12 seconds. This is the first empirical evidence that matter, antimatter, and photons all react similarly to gravity, which was widely predicted by standard theories of gravity but not previously tested directly. PrecursorSanduleak -69° 202, the progenitor star of SN 1987A, was a blue supergiant presumed to have a mass of about 18 solar masses. This required some revisions to models of high mass stellar evolution, which had suggested that supernovae would only result from red supergiants.Scientific studiesThe supernova remnant formed by debris from SN 1987A is one of the most-studied astronomical objects today.SN 1987A appears to be a core-collapse supernova which results in a neutron star. Since the supernova first became visible, astronomers have been searching for the collapsed core but have not found it. The Hubble Space Telescope took the sharpest images of the supernova to date. The images show no evidence of a neutron star. Two possibilities for the 'missing' neutron star are being considered. The first is that the neutron star isn't pulling in material from around it so it cannot be seen. The second is that the neutron star pulled in so much material that it further collapsed into a black hole. The latter option has been gaining support in recent years. TriviaSelected trivia about SN 1987A:
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