What factor in the progenitor star's environment often leads to complex, non-spherical planetary nebula shapes?

Answer

The star having a binary companion that redirects ejected gas

Complex shapes, such as bipolar structures or rings, are often sculpted by secondary, faster outflows or by interactions with material redirected by a binary companion star into denser rings or disks.

What factor in the progenitor star's environment often leads to complex, non-spherical planetary nebula shapes?
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