Why are stars and planets circular?

Why are stars and planets all round (exactly spherical)? Why not cubes or oval?

All can explain as follows.The shape of small objects (such as small size objects, people, houses or asteroids) is determined by its mechanical properties . For example, you can cut a slab into other shapes, the stone will not be able to restore its original shape due to the changed mechanical properties.

Meanwhile, the shape of larger objects is influenced quite a bit by gravity. Imagine, if you want to build a tall building, you have to have a strong foundation and the construction structure must be extremely solid, otherwise the building will collapse due to gravity.

Also, if a star / planet is cube-shaped instead of spherical, the corners of the cube will lie higher than the rest. At that time, the gravity of the star / planet will be unevenly distributed at the points and can no longer hold the equilibrium, causing the star / planet to fall out of orbit.

On the other hand, stars / planets in spherical form preserve the most optimal state, they can be affected by external forces but do not deform the original structure, leading to gravitational pull mix well at every point and keep it in orbit.

In fact, stars and planets are not standard spheres. They often bulge slightly at the equator.