I need help explaining the shape of this nebula Answered
This image is the "Butterfly Nebula".
I'm having trouble understanding it's shape.
According to the accompanying blurb, the shape indicates a "bipolar nebular, where fast-moving gas can escape more easily from the poles of the dying star than around its equator. This creates a lobed structure reminiscent of an hourglass, or, as in this case, a giant butterfly."
Why can the gases escape more easily from the poles? Why is it harder to escape at the equator?
Surely, if it was blasting from the poles, we would see a more linear shape, long "beams" of material shooting out of each end? This image looks to me as if material blasted away from the equator, but parallel to the poles, almost as if the two halves of the star's surface were peeled apart, like turning half an orange skin inside out.
Anybody got a borderline high-school/university level explanation for the shape?