|Picture dated November 16, 2011.|
The Sun burns, yes it is. For example burning of wood needs oxygen to ignite. The chemical components that make up that tree, such as carbon and hydrogen, in combination with oxygen in the atmosphere. So it is what we call combustion.
Sun, however, has a different burning. This is called nuclear fusion, which is very different from a combustion process. It seems that the Sun converts hydrogen to helium, and so there is an energy called gamma rays that do not need oxygen, but it requires extremely high temperatures and pressures. No need for any other element to create this fusion. So far our star has consumed half the reserves of hydrogen, since it exists, of 4.6 billion years.
So when we say that the sun is burning, we do not mean burning fire. The sun burns due to nuclear reactions, namely the collision of two hydrogen nuclei from which arises one of helium. This reactor strong as the sun or any other star, is not ceases its activity, due to enormous gravitational pressure in its core.