Stable+Stars+(main+sequence)

There are two forces acting on a star all of the time: It's a story of **gravity versus pressure**. The picture below shows hydrostatic equilibrium. The forces are balanced in the outer layers and the core.



Stars are hot balls of gas, When a star is fusing (burning) Hydrogen it remains in hydrostatic equilibrium for billions of years. A star such as this is called a main sequence star.

Larger stars have a shorter life because they burn their fuel quickly. The greater a star’s mass, the stronger the inward force of gravity and the higher the pressure and temperature in its core. The rate of fusion increases with temperature, causing massive stars to consume fuel much more rapidly than cooler less massive stars.

-->unstable stars