How does the sun burn without oxygen?

We all know that space is a vacuum. There is no air to breathe in space. It is also well defined that combustion needs fuel, oxygen and an ignition as explained in our previous post — Why water is non-combustible?

People always love a warm sunny day to start their work with. Sun is there at the centre of the solar system giving earth and the other planets light and heat for approximately 4 billion years now. When space is vacuum and has no oxygen, how does the sun burn?

Almost every fire that we see here in earth are carbon or hydrogen based fires. It is a chemical reaction where carbon based fuels like petrol burn in the presence of oxygen to form carbon dioxide and carbon monoxide.

Hydrogen based fuel burn in the presence of oxygen to form dihydrogen monoxide which is simply water.

The sun follows a different process to produce that enormous heat and light. It is called nuclear fusion reaction. It is not the normal combustion that you see in a campfire. It is true that sun has enormous amount hydrogen, but it is not burning the hydrogen to generate its heat and light.

In nuclear fusion reaction, the nuclei of two or more atoms are fused together to form a new heavier nuclei. In our sun, two hydrogen atoms fuse together to form a helium atom releasing energy in the process.

There is no need of any other materials like oxygen in this fusion reaction but, an enormous amount of pressure is needed. The pressure should be higher than the repulsive force between the two hydrogen atoms.

Usually in a nuclear fusion reactor, this type of pressure or heat is given by external forces. In sun and other stars, gravity is that force that takes care of this pressure. The gravity exerted by massive stars from the centre pulls everything inside, creating an enormous inward pressure that is much higher than the repulsive force between two hydrogen atoms.

This pulling pressure bombards two hydrogen atoms to form one helium atom and emits energy with respect to the law of conservation of mass and the law of conservation of energy.

The process takes place continuously making sure that the sun emits light and heat for these billions of years and more billions of years to come.

The sun dies out when it runs out of hydrogen which is approximately estimated to be a little over 4 billion years. We are in the middle of our sun’s life cycle.

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