Can somebody explain accretion of galaxies?
In: Physics
Short answer: In a cloud of randomly moving particles (whether those particles are dust or stars, it doesn’t matter), there is an average center of mass (where gravity will try to pull everything) and an average angular momentum around that center of mass. Since the particles can bump into each other (or in the case of stars, gravitationally attract each other in a way that mimics friction), all motion except for that average rotational speed eventually gets canceled out, flattening the mass into a disk. Gravity pulls things inwards, and due to conservation of angular momentum, the more things get pulled inwards, the faster they spin and the more they can resist being pulled inwards. Eventually, everything stabilizes into a spinning disk.
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