I understand there’s quite a few forces that prompt the disk shape of rings: particles in toroidal orbits interacting and cancelling their momentums; magnetic field lines being weakest farthest from the poles; corriolis effect drawing particles towards the path of least rotation; etc…
By why specifically the equator? Why don’t rings align with the poles, or some other angle? And why is this also the case for black hole accretion disks?
In: Physics
It’s the only arrangement that survives long enough to form real rings.
If it’s not a ring then particles in different orbits keep colliding with each other, eventually forming a ring.
Rotating planets are a bit wider at the equator so their gravitational field isn’t perfectly symmetric. Orbits not aligned with the equator precess: They change their orientation in space over time. Different orbits precess at a different rate. A ring that’s not aligned with the equator would become a cloud of of countless different intersecting rings over time, which then has collisions again, making a ring around the equator.
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