Why did the old stars of the Galaxy form a spherical subsystem, and the young ones – a thin rotating disk?

The oldest stars in the Galaxy occupy about the same space as the protogalactic cloud. The remaining gas was compressed towards the center and lost energy as a result of collisional processes. The new subsystems were smaller. Compression in the galactic plane was interfered with by centrifugal forces, and nothing interfered with the compression of the gas along the axis of rotation. As a result, a thin rotating gaseous disk appears in the plane of the Galaxy, in which the youngest stellar objects of the Galaxy are formed.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.