How is a main-sequence star like the sun able to maintain a stable size?
1 Answer
Due to Hydro-static Equilibrium.
Explanation:
During the main sequence stage the Star burns it's primary fuel that is hydrogen and converts it into helium, this process provides a balance against the inward acting gravity.
In a Star there is always gravitational force acting towards the inside of the Star. The only reason that the Star is not collapsing or even changing it's size is because it is generating enough force to balance that gravity so it has a Stable size.
Once the hydrogen has been consumed the Star will transform into another form but will not collapse as the fusion reactions will still be going on but with a different element.
The only way a Star collapses is when there is no outward acting pressure to balance gravity. This will only happen when the fusion reactions stop. For example when a Stars core contains only Iron as a product of previous fusion reactions. Iron is the most stable element so Star will not be able to fuse Iron into another element and hence will collapse on it's core.
