Viewing a single comment thread. View all comments

Steinway-Grand-D t1_j2yftto wrote

As far as I know galaxies are relativly flat. And I'd say our solar system is also quite flat too, when I look at the orbits of the planets. I've read that the reason is rotation? I can picture a new object coming into a flat system which already has a certain rotation and which will adjust over time to that system. But when and how did the rotation start and why does it seem like the vast majority is flat?

1

pepinyourstep29 t1_j38p65n wrote

It's angular momentum. The rotation starts when gravity begins pulling objects together. They have different masses and speeds so eventually they collapse into a sphere like a planet or star. These initial energies combine into a single moving object, which eventually goes from erratic chaotic rotations to one unified rotation over time.

Then anything of lesser mass will be pulled into the plane of rotation. So everything in the solar system eventually aligns to the same flat plane thanks to the sun's mass and rotation.

Same thing happens at larger scales, where galaxies are roughly flat.

Keep in mind that nebulae and elliptical galaxies exist as well. Under different circumstances things don't always turn out so flat.

2