Nothing can burn on earth without the presence of oxygen.
As what we call “fire” or “burning” is a chemical reaction in which atoms of oxygen combine with atoms of carbon from the fuel, the substance being burned, to produce carbon dioxide, light, and heat.
Since fire needs oxygen, and there is almost no oxygen in space, then how can the sun burn constantly? Well, the sun isn’t “burning” in the same sense that a fire burns on earth. The sun produces energy the same way that a hydrogen bomb produces energy.
In this process, hydrogen is changed into helium, but some hydrogen is instead converted into energy. So the sun continues to “burn” and produce light and heat without oxygen.
where the fire of sun came from???
sun is not burning, so there is NO FIRE. Just in this high pressure and temperature as inside of star, the nuclear reaction may occur. In this reaction created is radiation (passing energy), which we see as a visible light, and feel as heat. This what seems to be a fire, is a plasma (gas with free moving electrons, just like in metals, so able to conduct electricity).
The sun “burns” because of fusion, same as a hydrogen bomb, a nuclear bomb “burns” because of fission, a hydrogen bomb uses a nuclear bomb’s fission reaction to increase the pressure to start a fusion reaction in the hydrogen isotopes in the center.
Fission happens when the nuclei of a atom splits and some of the mass converts to energy.
Fusion on the other hand happens when nuclei of light atoms fuse together, to do this you need a lot of pressure, because the light atoms repulse each other.
More to the point, stars burn because enough mass has gathered in one place to increase the pressure from gravity enough smash the atoms of hydrogen together to produce helium.
As to why it start with hydrogen it is simple, it requires less pressure to start fusion then the rest of the atoms so it will ignite before the rest and the energy from this fusion will constantly put pressure outwards to combat gravity’s pressure inwards, once the hydrogen is used up the star consists of mostly helium from the fusion, helium has more mass then hydrogen which means higher gravity.
This means helium is now fused together and this continues until it starts making iron because iron atoms do not produce energy when it fuses which decreases the energy output, when that happens the balance between the gravity energy input and the fusion energy output is destabilized and the star starts to collapse (the harder the gravity pushes in the more atoms fuse and the more energy it produces to keep the star stable, this stops when iron is produced).
PS. the REALLY heavy metals are made in the center of the REALLY big stars where the pressure from gravity is just enormous, when they explode most of the energy goes outward but with like any explosion it puts heavy pressure on the center this forces the atoms in the center of the star to fuse like maniacs and we get heavy elements like platinum.
This stuff is fairly important to know because it tells you how the universe is made, scuze my typos, English is not my main language.