Although stars and planets in the universe have different sizes and masses, they are all spherical. So why are they all spherical and not any other shape?
The answer is gravity, a universal force that causes all objects to attract each other.
Low-mass asteroids and comets will have irregular shapes because their mass is not large enough to create enough gravity to evenly flatten them in the space environment.
When a celestial body has enough mass, its gravity will become very strong, enough to pull all parts of the celestial body to the center. Therefore, after millions and billions of years, the celestial body becomes more and more round. Therefore, massive celestial bodies will be spherical, although not perfectly spherical.
The Earth is not a perfect sphere, it is completely flattened at the poles and slightly bulged at the equator. Due to the Earth’s rotation force, the distance from the center of the Earth to the equator is 20km greater than the distance to the poles.
Meanwhile, asteroids and meteorites have very different shapes and are not fixed, not spherical. One of the reasons is because their mass is very small, so gravity is also very weak and not enough to deform the material layers. In addition, planets take shape early in their formation, when they are so hot that all the material appears to be melted. Its material layers were stable and shaped from the beginning because asteroids were fragments of collisions.
In short, celestial bodies in the universe with greater mass and stronger gravity will approach a more perfect sphere, such as a black hole that is rounder than the Sun, and the Sun is rounder than the Earth and Jupiter.
The most perfectly spherical object in the universe discovered by humans is Kepler 11145123 (or KIC 11145123) discovered by NASA’s Kepler space telescope. According to researchers, Kepler 11145123 is 5,000 light years away from Earth, with an equatorial and polar diameter difference of only 6km, although the diameter of this star is 3 million km.