What physical process generates a force inside a pre-main-sequence star to offset the force of gravity and stop the star from slowly condensing and shrinking, thus producing a stable, non shrinking main-sequence star?

Question

Nolan Aldridge · Accepted Answer

Hydrostatic equilibrium keeps a pre main sequence star from collapsing.

As a cloud of gases, mostly hydrogen, collapses because of gravity, the temperature rises and an outward thermal pressure is created. This process is how stars are formed. The star is said to be in hydrostatic equilibrium when the outward thermal pressure equals the inward gravitational force and the star ceases to collapse. Before entering the main sequence, newly formed stars usually go through multiple stages of gravitational collapse and hydrostatic equilibrium, during which the core temperature rises to a point where fusion reactions can begin.

Audrey Arnold · Answer

undefined In order to keep a main-sequence star stable, the fusion of hydrogen and helium in the star's core creates an outward pressure that opposes gravitational collapse.