Task: Sentence Expansion
Input (English): As luminosity of stars increases greatly with mass , the luminosity of hypergiants often lies very close to the Eddington limit .
Output (English): As the luminosity of stars increases greatly with mass , the luminosity of hypergiants often lies very close to the Eddington limit , which is the luminosity at which the radiation pressure expanding the star outward equals the force of the star 's gravity collapsing the star inward .