What must balance to maintain hydrostatic equilibrium in a gas cloud?
Answer
Outward thermal pressure and inward gravitational force
Hydrostatic equilibrium describes a precarious balance within an isolated cloud of gas and dust before star formation truly begins. In this state, the cloud is stable against collapse or expansion because the forces acting inward are exactly counteracted by forces acting outward. The inward force is the self-gravity exerted by the cloud's own mass pulling all its material toward the center. The opposing outward force is generated by the kinetic energy of the gas particles, known as the thermal or gas pressure. When these two forces—gravity pulling in and pressure pushing out—are equal, the cloud remains in hydrostatic equilibrium.
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