text: A baratropic star with  and  is stable if the quantity
  is non-negative for all real functions  that conserve the total mass of the star .
  where
  * is the coordinate system fixed to the center of the star
  * is the radius of the star
  * is the volume of the star
  * is the unperturbed density
  * is the small perturbed density such that in the perturbed state, the total density is 
  * is the self-gravitating potential from Newton's law of gravity
  * is the Gravitational constant