The story of Supernova 1987 A
Ocurred in Large Magellanic Cloud, 170 thousand light years from us.
Progenitor star: Sanduleak -69o 202, a blue supergiant.
Discovery
- 24 February, 1987
- in Tarantula Nebula in Large Magellanic cloud,
- by Ian Shelton, University of Toronto,
- at Las Campanas Observatory, Chile.
Is the theory right?
At the core of the theory, so to speak, is the production of vast
numbers of neutrinos.
Neutrino detectors available at the time.
Prediction: each detector should see 10 or so neutrinos from
SN 1987A in a space of about 10 seconds.
Results.
Timing (times in Universal Time)
- 7:36, 23 February, neutrinos observed
- 9:30, 23 February
- Albert Jones, amateur astronomer, observes Tarantula Nebula in LMC
- He sees nothing unusual
- 10:30, 23 February
- Robert McNaught photographs LMC
- When plate is developed, SN1987A is there.
- Some 20 hours later, Ian Shelton's discovery.
Conclusion:
- It took between two and three hours for the shock wave to get to
the surface of the star.
- This agrees with the model prediction.
One surprise:
- It was thought that type II supernovae came from red supergiant
stars, but the star SK -69 202 was a blue supergiant (~ 20 times smaller
than a red supergiant.)
- It took some thinking to conclude that some very evolved stars could
have a smaller size with higher surface temperatures.
- SN 1987A was not as bright as moster type II supernovae. This
was explained based on its smaller initial size.
- Initially, because it was small, there was not so much surface
area to be radiating. Also, it was so hot it radiated mostly in the
ultraviolet, not the visible, so some of the radiation was not seen.
- After it expanded greatly, it was cool enough to be radiating
mostly in the visible.
- But by then a lot of its energy had been expended in the expansion.
Davison E. Soper, Institute of Theoretical Science,
University of Oregon, Eugene OR 97403 USA
soper@bovine.uoregon.edu
