““A star is a body that is massive enough for the gravitational comptession at its centre to produce a temperature great enough for nuclear reactions to occur spontaneously. When this ignition temperature is achieved, nuclear reactions in the central region will produce an energy outflow that is eventually radiated away from its surface in the form of heat and light. The star is kept in equilibrium by the balance between its internal pressure and gravity. This is a stable balance because if the gravitational force were made slightly greater then the star's centre would be squeezed a little more, so producing faster nuclear reactions and hence a corresponding extra pressure pushing outwards. Thus a balance is quickly restored.””
