How is there fire on the sun when there’s no oxygen?
Strictly speaking, oxygen is a part of what makes up the sun’s composition. Meanwhile, although the sun appears fiery, there’s no real fire on the sun at all. You get fire when a substance — a fuel — quickly combines with oxygen in the air — so quickly that light and heat are given off.
For most of human history, people envisioned the sun as a ball of fire — until scientists discovered nuclear fusion in the early 1930s. In fusion reactions, two atoms come together to produce a heavier atom. In the process, they release energy and elementary particles. Nuclear energy or the sun energy is a stronger kind of energy than fire. In just one second our sun emits more energy than humans have used in 10 thousand years.
To create sun energy from fusion, you need high temperatures and great densities — like those deep inside of stars. Thus it’s fusion, not fire, that powers the stars we see as we look up on a starry night.
The sun’s been around for over four and a half billion years. It has enough nuclear fuel to stay much as it is for another five billion years.