Final answer:
Hydrostatic equilibrium is the state in a star where gravity's inward pull is balanced by internal pressure, crucial for the star's stability.
Step-by-step explanation:
The concept in a star or other fluid body where gravity's inward pull is exactly balanced by internal forces due to pressure is known as hydrostatic equilibrium. This state of balance ensures that a star, such as our Sun, maintains its structure and doesn't collapse under its own gravity. For stable stars, maintaining hydrostatic equilibrium is essential. This equilibrium is like a delicate dance between the inward force of gravity and the outward pressure exerted by the hot gases. If the balance tips, the star can either collapse or expand until a new equilibrium is reached. In our Sun, the temperature at the center is hot enough for proton-proton fusion, which helps to create the internal pressure that combats the force of gravity.