Non-Spherical Stars

An anonymous reader writes "Now that the large interferometers are coming on line, the stars are no longer dots. Achernar (Alpha Eridani), is a huge ellipsoid whose polar radius (due to fast spinning) is 50% smaller than the equatorial one!"

Comments

Energy output

[VendingMenace]

50% smaller? Wow, this must be spinning incredibly fast. With so must mass being displaced from where it would be in a sphere, it must effect the pressure inside the star. As such, i wonder how much this effects the fusion within the star. Since fusion is driven by the compressional forces of the suns mass, the effective reduced mass must reduce the energy output of this star. RIght?

Perhps i don't really kow what i am talking about.

Black holes must be flat dishes

[Frans Faase]

If you extend this idea to very fast spinning black holes, you end up with the idea of a spinning disk which "radius" in one direction is
maybe only a few percent of the radius in the other directions.

Who writes these articles? Or am I iggernint?

[Atario]

Due to its daily rotation, the solid Earth is slightly flattened...

Solid Earth? Only the surface (and part of the core) is solid, right? The rest is [Dr. Evil] liquid hot magma.

The observed flattening cannot be reproduced by the "Roche-model" that implies solid-body rotation and mass concentration at the center of the star.

I thought stars were pretty much all plasma, which is to say, a fluid. Why, therefore, should stars obey any "solid-body" rule at all?

Theoretical maximum for common stellar materials?

[Raindance]

Any physics buffs know what the largest theoretical ratio would be between a star's polar radius and equatorial radius, for the stuff that stars are made out of? Is the ratio for this star anywhere close to that?

I'd imagine one can only attain this through centrifugal force, which necessarily puts structural stress on the star, and past a certain amount of structural stress stars should disintegrate.

Re:Theoretical maximum for common stellar material

[CheshireCatCO]

I believe a star has zero tensile strength* (it's just a fluid), so once you're spinning too fast for gravity to hold you together, it's bye-bye time.

The better question is this: how did that star form? If it was spinning too fast to hold together, how did it accrete matter with that much angular momentum at all?

* Barring magnetic fields, mind you. But you'd need an ass-kicking field to hold a star together very long, I would think.

Hal Clement

[IPFreely]

As soon as I read this, I thought of Mission of Gravity, a book about a flattened planet, Jupiter size, 18 minute rotation, Surface gravity at the equator was about 3 Earth G, while at the pole was more like 600+ Earth G, flat just like this. It was written in 1953 I believe, and included some detailed physics in the back of the book covering how the planet maintains it shape.

The story is about natives on the planet, but the physics alone is worth the read. It's quite a strange place.

Implications on stellar death

[MeowmiXXX]

I wonder how this will affect it's distruction, the decreased pressure would decrease the rate of fusion while the spinning would make it easier to fly apart, and how would it die off? Since, it wouldn't have much growth before the centrifugal forces rip it apart it should be hotter and more compact.