Because the blast wave from the original explosion in 1987 is expected to overrun the material ejected by the star in the years just before it detonated. This shell is material at rather high density, and when the blast wave impacts it, a compression shock will be created which will amplify the local magnetic field and accelerate the plasma to high energies. It will produce a bright X-ray source and a source of 'non-thermal' radio emission visible to radio telescopes. There may also be significant optical light produced, which for a time make the supernova remnant just barely visible to the naked eye again.
Copyright 1997 Dr. Sten Odenwald
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