# Could a bipolar nebula be produced by a time gradient?

M2-9 is an example of a bipolar nebula that resembles two back-to-back rocket nozzles. Is it possible that this shape (somewhat unusual for an explosion) is the result of a time gradient? A rotating neutron star having collapsed and preserved its angular momentum with an equatorial velocity of relativistic proportions would be at a significantly different time than the poles of the star. Frame dragging would spread this effect out from the equator to neighboring space. A nova exploding under these conditions would be constrained outward at the poles since the relativistic time gradient puts the space near the equator in the future, relative to the poles, and would not share the same "now," making that space inaccessible to the expanding explosion. Something rotating at much slower speed would explode in a more spherical manner.

Is this a plausible reason for the shape of bipolar nebulae?

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Well, the equatorial velocity of a neutron star isn't more than $9 \times 10^7 \text{ m/s}$, which gives a $\gamma$ factor of $\sim 1$ (it's actually $1.08$, but that doesn't make a large difference to time dilation effects).