How was the sun formed?
(Lansing State Journal, October 11, 1995)
Because of the rotation, the cloud flattened and much of the matter became concentrated at its center. Gravity fundamentally depends upon mass and distance; the more massive an object, the stronger the attractive force it exerts on other objects.
At the center, strong gravitational forces confined particles to a relatively small space. As a result, temperatures increased.
Over time, enough matter collapsed upon the center that it was heated to the point where nuclear reactions could begin. A star was born.
Nuclear reactions within the core of a star release enormous amounts of energy and create an outward pressure that prevents further collapse.
It is this balance between pressure and gravity that keeps a star like our sun stable.