How are Shell-type Supernova Remnants typically characterized morphologically?
Answer
By a prominent, relatively thin, and often circular shell of emission enclosing a relatively empty interior.
The Shell-type morphology is the most common visual classification for supernova remnants. This structure is defined by the compression of gas into a distinct boundary due to the strong forward shock wave interacting with the unshocked interstellar medium (ISM). This compressed material forms a visible shell, frequently appearing circular or ring-like in images across radio or optical wavelengths. This morphology is often associated with remnants that are well into the Sedov-Taylor or early Radiative phases where this distinct boundary layer has fully formed.
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