Why does the Cygnus Loop appear as separate wisps instead of a continuous cloud?
This nebula is the product of a supernova explosion; in this section, the blast wave has encountered an area of dense interstellar gas, creating turbulence in the wave and causing it to glow. The picture is a composite of three images taken by the Hubble Space Telescope.
The Cygnus Loop appears as a series of distinct wisps rather than a continuous cloud because of the nature of the interstellar medium through which its shock wave is traveling.
As the supernova remnant expands, its shock wave encounters small, localized clouds of denser material within the surrounding interstellar space. This interaction creates the observed patchiness, as the shock wave illuminates these denser regions, resulting in the filamentary structure characteristic of the nebula.1