Because when the mass of a star reaches a certain level (whether it is a star, a planet or a satellite), the gravitational squeezing will lead to the deformation of the inner core, and the larger gravitational squeezing of the star will lead to the melting of the inner core, so the structure and shape of the star will change. Moreover, the distance from each point on the sphere to the center of the sphere is equal, and the gravity of the center of the sphere is also equal. The energy consumption of spherical circular motion is lower than that of angular polygon, that is, the energy consumption is the lowest. The rotational motion of a sphere is smaller than that of an angular polygon, that is, the energy consumption is the lowest. Sphere has the largest surface area, the most uniform thermal expansion and cold contraction, and the smallest space resistance.

The function of gravity is infinite, and the repulsion between molecules is much stronger than that of gravity, but it only works when the molecules are close together. When gravity tightly squeezes all parts of the star and gradually contracts inward, when the degree of contraction is too high, the repulsion between molecules will be stronger than gravity, which will cause these molecules to be pushed outward. When these molecules are pushed away from each other by repulsion, the repulsion will fail and gravity will immediately pull them back again. Take the earth as an example. When a part of the earth rises excessively (if Mount Everest is ten times higher), the crust at the bottom of the mountain will collapse because it can't bear the gravity of the giant peak, and the buoyancy generated by the lava inside can't support the weight of the peak. The summit will sink into lava, and the raised part will gradually sink into the earth.

Beyond the universe or the universe, let's compare. If the universe is a nucleus, then the multi-layer electronic layer outside the nucleus is covered by many spherical cosmic layers just like the multi-layer universe outside the universe. For example, the solar system is approximately spherical, many spheres similar to the sun revolve and rotate to form the Milky Way, and the Milky Way is also approximately spherical.

If the shape of the earth is not "round", the phenomena caused by gravity and repulsion will constantly adjust its shape. When the parts are adjusted to the equilibrium state by gravity and repulsion, the earth will approach a circle. When the mass and gravity reach a certain level, any star, planet or satellite will become spherical. The minimum requirements are about 800 kilometers in diameter and 500 million tons in mass. Stars smaller than this lower limit are irregular in shape.