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The Question

(Submitted November 07, 1996)

Is it possible that the Sun could just burn out? What manages to keep the Sun so hot all of the time?

The Answer

The Sun is basically a thermonuclear bomb with a built-in thermostat. Just as in a hydrogen bomb, hydrogen atoms are fusing together to make helium atoms and this nuclear reaction produces heat (along with the light that we see). If the reactions go on too fast, the Sun expands slightly (just like a balloon expands when you heat up the air in it). This slows down the reactions and then the Sun cools and contracts. If it contracts too much, the nuclear reactions speed up, and then the Sun heats up and expands again. So the Sun stays at the same temperature, burning its nuclear fuel at a steady rate. At the rate it is going, we have about 4 billion years left until the Sun burns out

Andy Ptak and the Ask an Astrophysicist team

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