Final answer:
Main sequence stars are indeed in hydrostatic equilibrium, balancing gravitational forces with internal pressure resulting from nuclear fusion.
Step-by-step explanation:
The statement that main sequence stars are in hydrostatic equilibrium is True. Main sequence stars, including our Sun, achieve a balance between the inward force of gravity and the outward pressure produced by nuclear fusion at their cores. When a star reaches a central temperature high enough (approximately 10 million K), it can fuse hydrogen into helium, marking the star's entry into the main sequence. This process leads to a state of equilibrium where the star's rate of change slows down considerably. The star's structure is determined by two main factors: its total mass and the composition. Hydrostatic equilibrium is crucial for a star's stability; it ensures that the internal pressure is enough to support the weight of the star's outer layers, maintaining its shape and preventing collapse or uncontrolled expansion.