THE GRAVITATIONAL POTENTIAL ENERGY PROBLEM

From The Encyclopedia of Physics (Lerner, 1991):  “The infant sun began to contract under the force of its own gravity.  Although these early stages of collapse are not well understood, it is suspected … such an object will emit infrared light as gravitational potential energy is converted into thermal kinetic energy.  As the central regions contract faster than the surface layers, the central temperature quickly rises to the ignition temperature for thermonuclear reactions, nearly 10⁷ degrees.”  [p. 1189, emphasis added].