Straight sides are unusual, whether a view of a cylinder or otherwise. What causes that?
Not sure. Maybe nearby shock fronts (from supernovae) are a factor, or perhaps the star's spin rate influenced the direction of material ejected. Binary systems would produce weird nebulae too. Lots of planetary nebulae are strange-looking; astrophysicists are still studying the possible causes (that's scientist-speak for "we don't know").
