Stars and planets differ in terms of the forces at play within them.
In a star, the balancing forces are indeed gravity inward and pressure outward. The intense gravitational force in a star's core is responsible for compressing and heating the material. As the temperature and pressure increase, nuclear fusion reactions occur, converting hydrogen into helium and releasing an enormous amount of energy. This energy generated by fusion creates an outward pressure called radiation pressure, which counteracts the gravitational force pulling the star inward. In the core of a star, these two forces, gravity and pressure, are in equilibrium, allowing the star to maintain its stable state.
On the other hand, planets primarily rely on gravity to maintain their balance. Planets are not capable of sustaining nuclear fusion reactions like stars, so they do not generate radiation pressure. Gravity is responsible for pulling matter together to form a planet, and it continues to exert a force toward the center of the planet, creating a pressure gradient within the planet's interior. The pressure increases with depth due to the weight of the overlying layers. This pressure gradient is what balances the gravitational force.
In summary, while stars have two balancing forces, gravity inward and pressure outward (including radiation pressure due to fusion), planets primarily rely on gravity to maintain their balance. Planets do have pressure, but it arises from the weight of their own material and the resulting pressure gradient within their interiors. Gravity is balanced by this internal pressure gradient in planets.