How does the sun keep burning?

Published February 20, 2023

How does the sun burn?

Have you ever wondered how the sun burns? What fuel does the sun use? Will the sun run out of oxygen? Will the sun burn forever? This blog post answers a few of the frequently asked questions.

Sun in January 2023. Photo credit: NASA (January 2023. Photo credit: NASA)

How does the sun burn?

The sun does not burn like the way regular firewood burns. When firewood is set on fire, what happens is combustion. Combustion is a chemical reaction where an object - like firewood - reacts with oxygen to give heat and light. Combustion is an exergonic or exothermic chemical reaction.

The sun does not use combustion to "burn". Instead, the sun uses a different process called nuclear fusion where every second, 700 million tons of hydrogen converts into 695 million tons of helium. Energy is released in the form of gamma rays, and these gamma rays are converted to light. Nuclear fusion does not require oxygen.

Will the sun run out of oxygen?

No. Since there is no combusion taking place, the sun running out of oxygen is not relevant.

However, since there is nuclear fusion taking place, the amount of hydrogen is relevant. The sun has used up about half of its hydrogen fuel supply in the last 4.5 billion years. In 4.5-5 billion years ,the sun will run out of hydrogen and get out of its stable phase.

How old is the sun?

The sun is about 4.5 billion years old. Our solar system was also formed 4.5 billion years ago.

Is the sun noisy?

Yes, the activity inside the sun creates sound waves. Sound waves travel fast and smash into each other. That causes vibrations. Solar flares are caused when powerful bursts of energy shoot out of the sun. This also creates quakes inside the sun.

Sun in February 2023. Photo credit: NASA (February 2023. Photo credit: NASA)

I have a previous blog post about the Solarium in NASA Goddard. The video I took includes the sound that's made by the sun.

Will the sun burn out one day?

Yes, the sun will burn out when all the hydrogen runs out. At this point, the sun begins to die. This dying process will take in 2 - 3 billion years as the sun goes through the phases of star death.

When will the sun die?

In about 5.5 billion years, the sun will run out of hydrogen. It will then burn helium and start expanding. It will then transform from a yellow giant to a red giant. At that point, it will expand beyond to the orbit of Mars. Before that it will engulf our planet Earth. The core of the sun will shrink, but the outer layers expand up to Mars.

Is there anything we can do to save the sun?

No. If you have watched a movie where astronauts set off a nuclear bomb in the sun and try to jump start it, just nope!

After 5 billion years, the sun will run out of its fuel. Theoretically, to save the sun, the sun needs to be "stirred" with a giant ladle or stirrer so that unburned hydrogen from its outer layer - the convective zone - would need to be shoved into the core. Another option is to crash a star into the sun to add to the fuel. A third option would be to create multiple red dwarfs. Stars with less than one third of the masss of the sun do not have a radiative zone and are convective. They mix all their hydrogen into the core, so there's a much longer supply of fuel. This way, the light of the Sun will be lesser, but the lifetime will increase dramatically.

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Last Updated: February 20, 2023.     This post was originally written on January 08, 2023.