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I need help explaining the shape of this nebula Answered

http://www.esa.int/spaceinimages/Images/2014/10/Butterfly_death_throes

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."

But... why?

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?


Discussions

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Burf

4 years ago

What you are seeing in the picture is a two dimensional rendering of a three dimensional object. In true perspective, the wings are actually conical blasts of dust and gas spewing out the north and south poles of the magnetic field.

Imagine two ice cream cones with the pointy ends stuck in a tennis ball. Depending on your point of view, the visual shape would vary. If you were to rotate the nebula 90 degrees along the north-south plane, the wings would appear as circular discs, denser near the middle than the outer edges.

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KitemanBurf

Answer 4 years ago

I get that (that's what I was trying to explain with the orange-peel reference). What I don't get it how that shape formed.

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icengKiteman

Answer 4 years ago

Perhaps a star five times our Sun, turned oval can succeed at pulling back expelled material to the wide diameter spinning equator causing said material to heat by friction and flow out of the lesser G field presented at the polar regions.

Similar to the outside of an event horizon described for black hole accretion disc.

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steveastrouk

4 years ago

Presumably the magnetic field around the star is guiding the movement of these ionised gases ?

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Kitemansteveastrouk

Answer 4 years ago

I guess so, but how? The only other things I've read about magnetic fields shaping stellar explosions, the bulk of the material has blown off at the equator, with narrow "beams" of matter guided out of the poles at very high speeds.