What causes the outward pressure of the star?

The outward pressure of a star is primarily caused by nuclear fusion occurring in its core, where hydrogen atoms fuse to form helium, releasing immense amounts of energy. This energy generates radiation pressure, which pushes outward against the gravitational forces trying to collapse the star. Additionally, thermal pressure from the high temperatures within the star contributes to this outward push, maintaining a balance with gravitational forces and allowing the star to remain stable.