THE SUN IS ON FIRE, I REPEAT, THE SUN IS ON FIRE.
[Cue Angwe’s pedantic ass music!]
The sun, alas, is not on fire. It’s a plasma. All over. Pretty much everything on the sun is a superheated gas.
Fire, as we usually define it, is the exothermic output of combustion, through physio-chemical processes. Wood burning, for instance, is complex carbons + heat + oxygen, and gives us a sustained reaction of carbons breaking down and releasing more heat energy. Other fires are much the same: thermite burns hotter and so requires a bit more of a reaction to get started (you generally need some magnesium, which burns hotter than your average match), but is still thermite + heat + oxygen = a whole lot of new heat energy + leftover compounds.
A plasma is a little different. The gravity of something the mass of the Sun is not going to stop compressing. And when you compress things, you raise their temperature. Take a box of stuff. Any stuff. Doesn’t matter. Now heat it up. A lot. No I mean really a lot. Keep heating it. As you heat stuff up, it breaks down into simple things. Solids become liquid. Liquids become gases. Eventually, gases become plasmas, which are superheated gases that behave a little differently than your average gas, so much so that plasma physics is its own branch.
So, when you’ve got a giant ball of gas, compressing under its own gravity, heating its core to millions of degrees, starting a continuous chain reaction of nuclear fusion, building hydrogen into deuterium and then helium, everything is so hot its not a gas, its just all a plasma.
Plus, you don’t want to be anywhere near a star that’s “on fire”. The closest thing I can think of is the thermonuclear reactions happening outside the core, which happens each time a star moves through heavier elements at the end of its life, each of which also causes the star to puff up (in the Sun’s case, going through red giant stages) and then eject outer layers. It looks pretty from far away - that’s what planetary nebulae are - but would be distressing up close…and hazardous, as the star grows. Also, if it’s bigger than the sun, there’s the possibility of a supernova of one kind or another. (Type II if it’s just big, but not big enough for gravitational collapse, Type I if it’s small enough to form a white dwarf, but has a nice companion to pull matter from.)
[End Angwe’s pedantic ass music!]
I like science. It’s fun.