How does star blow up ? A hot bright star blows up when it runs out of fuel. Heres why that happens. The force of gravity is always puling the matter in the star toward the center. But in that center, small bits of matter called atoms are always fusing together, making bigger atoms and releasing huge amounts of energy. That energy pushes outward and works against the gravity during the stars life. After many millions of years, the star runs out of small atoms. Then it has no more energy to push outward. The star collapses, and when the matter collides in the center, it explodes. Subscribe- @TodayILearn 194 views11:53