The oldest stars in the Galaxy (Population II stars, globular clusters) form a spherical halo around the Galaxy which leads astronomers to conclude that the protogalactic cloud (the cloud from which our galaxy formed) was roughly spherical.
Protogalactic cloud can be defined as, a protogalaxy, which could also be called a "primeval galaxy", is a cloud of gas which is forming into a galaxy.
A protogalactic cloud with very little angular momentum is more likely to form an elliptical galaxy (spherical) than a spiral galaxy.
The higher gas density forms stars more efficiently, so all the gas is converted into stars before a disk can form. This is why a dense cloud can more likely to produce an spherical galaxy.
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