The outward pressure that prevents a star from collapsing is produced by which process?

• A. Nuclear fusion
• B. Chemical reactions
• C. Magnetic confinement
• D. Radiation pressure

Answer: (A)

The pressure that opposes gravity in a star mainly comes from hot, glowing gas in the core (and, in some cases, from photons pushing outward). The heat and light that keep that gas hot come from energy released by nuclear fusion happening in the core. That fusion energy raises the temperature, increasing the gas pressure so the inward pull of gravity is balanced. In other words, the ongoing fusion reactions provide the energy that sustains the internal pressure needed to support the star. Radiation pressure can contribute, especially in very massive stars, but it’s a consequence of the fusion-powered energy flowing through the star, not the separate process that creates the support.