Final answer:
The hydrostatic equilibrium in the Sun is a balance between gravity, trying to contract the star, and the thermal gas pressure caused by nuclear fusion in the core, trying to expand it. This balance maintains the Sun's stable structure, preventing it from either collapsing or expanding significantly.
Step-by-step explanation:
The hydrostatic equilbrum in our sun is a balance between the inward force of gravity and the outward force of gas pressure. This equilbrium ensures that the Sun, as well as other stable stars, are neither expanding nor contracting significantly over time. In the Sun's core, nuclear fusion processes, specifically the fusion of hydrogen into helium, release energy (approximately 26 MeV per reaction), providing the required outward thermal gas pressure.
This pressure counteracts the immense gravitational force trying to collapse the star, thereby maintaining a stable structure. This careful balance allows the Sun to exist in a state of hydrostatic equilibrium, comparable to the stability of an inflated balloon, where the internal air pressure balances the external air pressure.