What does 'stable star equilibrium' refer to?

Stable star equilibrium refers to the condition where the internal forces of a star are balanced, primarily between gravitational forces pulling inward and the pressure from nuclear fusion in the core pushing outward. In a stable star, the gravitational force trying to collapse the star is countered by the thermal pressure generated from reactions occurring in the star's core.

At this equilibrium state, the star neither expands nor contracts significantly over time, as the forces are perfectly balanced, maintaining stability. In this context, it’s essential to differentiate this from other interactions, such as those between a star and its planets, or within the nuclear core alone, which do not encapsulate the holistic balance required for stable star equilibrium. Therefore, the concept of stability arises specifically from the internal forces acting within the star itself, making this understanding crucial in astrophysics.