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Why does the Cygnus Loop appear as separate wisps rather than a continuous cloud?
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Supernova
Composite image of Kepler's Nova, or Kepler's Supernova, taken by the Chandra X-ray Observatory.
The Cygnus Loop appears as a series of separate wisps rather than a continuous cloud because of the nature of the interstellar medium into which its shock wave is propagating.
The most widely accepted scientific interpretation is that this medium contains small, localized clouds of denser material. As the supernova's expanding shock wave encounters these denser regions, it creates the striking, patchy filamentary structure observed today, rather than a uniform shell of gas.1