star rotation

[atexan]

As dust coalese into stars, at what point in star formation & from what force does rotation begin ? Would also apply to galaxies.

[Chris Peterson]

As dust coalese into stars, at what point in star formation & from what force does rotation begin ? Would also apply to galaxies.

The material is really rotating from the beginning, because the net angular momentum of the system is non-zero. As the mass collapses and becomes denser towards the center, the speed of rotation increases, as required to conserve angular momentum. What happens is you get a filtering process: at the beginning, you have material rotating at different speeds, on different planes, and in different directions. As it contracts, angular momentum is transferred between particles by collisions and electromagnetic effects. This both normalizes the orbits of material near the overall average, and ejects material that is far from it. What's left ends up orbiting more or less together- a rotating star or rotating galaxy.

[BMAONE23]

Isn't it similar, though through differing causation, to why water forms a whirlpool when going down a drain? Each H2O molecule imparts angular momentum on the group as it travels toward the drain causing the mass to spin. Otherwise the water would just pour down the drain without making a whirlpool.

[geckzilla]

I don't think it's quite the same because the whirlpool around a drain can be explained by subtle variations in the shape of the sink causing the water to flow in a certain direction each time. Also it matters a lot from what position the water is poured into the sink from.

[Chris Peterson]

I don't think it's quite the same because the whirlpool around a drain can be explained by subtle variations in the shape of the sink causing the water to flow in a certain direction each time. Also it matters a lot from what position the water is poured into the sink from.

Regardless of the mechanism that gets the spin going in the first place, however, the water going down a drain does speed up its rotation as it gets closer to that drain for the same reason that stars and galaxies spin: the conservation of angular momentum.