Shell type Remnants

The Cygnus Loop is an example of a shell type remnant. As the shock wave from the supernova explosion plows through space, any interstellar material it encounters becomes heated and stirred up -- thus producing a big shell of hot material in space. We see the ring-like structure because when we look at the edge of the shell, there is more hot gas on our line of sight then when we look through the middle. Astronomers call this limb brightening.

Image credit: Levenson et al.

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