What Happens as a Star Runs Out of Hydrogen?
ES2810  Small Stars

Stars less than 40% as massive as the sun are known as red dwarfs. Examine how these small stars use their hydrogen fuel and what happens as their hydrogen supply is depleted.

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Red dwarfs are totally convective stars—the energy released by fusion in the star’s core is carried to the surface by the circulation of matter in the star. As the stellar matter is always mixing, a helium core does not accumulate.

This type of star fuses hydrogen into helium very, very slowly. When a red dwarf's hydrogen supply finally runs out, in hundreds of billions of years, astronomers hypothesize that gravitational forces will overcome decreasing outward pressure, compressing the star into a planet-sized white dwarf. Scientists currently estimate the age of the universe to be around 14 billion years, so all red dwarf stars still are far from running low on fuel.

7. Describe the final form of matter for medium- and small-sized stars.

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