What fundamental physical principle causes a large stellar mass to naturally settle into a spherical shape?
Answer
Gravity causing the configuration to minimize its potential energy.
Gravity is the essential force driving the initial spherical configuration of any sufficiently massive object, including stars. Gravity pulls all mass inward equally toward the center of mass. This continuous inward pull results in the configuration that requires the least potential energy, which, in three-dimensional space for a collection of matter, is a sphere. This principle dictates that the star itself is nearly a perfect sphere, and consequently, the initial shell of gas ejected via the gentle stellar winds, which originates from this spherically symmetric source, is also expected to be spherical, akin to an expanding soap bubble.
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