Why do stars start spinning after they form?

Question

I was just reading my scientific american and i noticed that they said that a cloud of gas condenses into a spinning proto-star. Why would it always be spinning? And furthermore, why are solar systems and galaxies always only 2 dimensional?
And what the hell, im feeling inquisitive, why the hell is everything spinning? Planets, moons, galaxies, particles? Isnt it possible that something(particle or galaxy) is not spinning relative to me perspective, or is it just unlikely?

Answer 1

When gravity brings things together in space, it is unlikely that they will be aimed directly at each other. 99.999999% of the time, they will swing past one another. If they end up in orbit around one another, it's because they have lost kinetic energy thru collisions; but their total anglular momentum is not changed.



After billions of collisions, small particles join into large ones, and the angular moment of the whole system remains constant. For angular momentum to remain constant while the radius of the orbit is reduced, it is necessary for the orbital period to get shorter and for kinetic energy to be lost.



Orbital dynamics cause planets to shepherd one another so that they pull one another into the same plane. Each near miss results in both orbits moving closer to the same plane.

Answer 2

You mean like the Earth is actually sitting still and everything else spins around it?

Well not only is a spinning earth easier mathematically but it matches observations like the Coriolis effect.



About why stars and galaxies spin, if the condensed from dust clouds and angular momentum would be conserved. Even if it was a very small rotation to begin with it would be a huge effect after the matter condensed. It would be 2D because you can only spin a body on one axis at a time.



Now the question about why does everything spin is the interesting one.

"Why does everything spin?" is a great question.

It would be a good question to ask a university physics lecturer.

Subatomic particles like quarks and electrons apparently all have spin and if I understand it right can spin in at least 3 dimensions.



That really is a tough one and I would love to see the answer.

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Another question I have never seen a good answer to is about how "Newton's water bucket" would be able to tell if it was spinning. Newton used it to posit something he called absolute space.

Mach disagreed with Newton's interpretation and it is still unresolved.

Relativity proposes no absolute fixed frame of reference.

Answer 3

1. Stars do not start spinning after they form. They form from clouds of gas and dust that are all ready in motion and the existing angular momentum is conserved. To conserve the angular moment the gas spins faster as it gets smaller.



2. It's not so much that everything should be spinning as entropy makes unlikely that things not have some net spin.



3. Solar systems tend to be two-dimensional (i.e. lie mostly in one plane) because as the proto-star collapses the portions that are circling in other planes collide with each other and minimizes motion not in the plane.



4. See 2.

5. See 2.

6. See 2.

Answer 4

If you think about it, for something to form that wasn't spinning all the stuff that formed it would have to be moving straight towards it's centre of mass, with no tangetial velocity at all- which is very very unlikely!



For the 2D question, it's basically because when thing spin they tend to bulge out in the middle, so that is why galaxies tend to be a bit flat. But they aren't perfectly 2D by any means.



Oh and as to why particles all spin, that is a much harder question as fundamental particles aren't that well understood.

Answer 5

When a cloud of gas begins to compress toward its centre of gravity the molecules always travel in a curved path, they spiral inward in the same direction, this starts a turning motion which the star maintains when it forms, the same conditions apply when planets form from an accretion disc.

Answer 6

Spinning in 2 dimensions is normal stasis for matter/energy flow in the cosmos. You might also ask why planets don't orbit the Sun in more than one direction, but hopefully the answer is obvious after billions of years of 'settling down'.

Answer 7

Conservation of angular momentum. Google it!