sentence: Most stars use up the hydrogen at their core.
sentences_after: When they do, their core shrinks and becomes very, very hot. It becomes so hot it pushes away the outer layer of the star. As the outer layer expands it makes a red giant star. Astro-physicists think that in about 5 billion years, the sun will be a red giant. Our sun will be so large it will eat the Earth.
concept_name: star
headings: Star Birth and life and death of stars
categories: Astrophysics