In the sun's core, we know it's very hot.
I was curious to research why it was exactly and I think 99% of answers are not fully correct. They say that it's because of nuclear fusions.
I'd not agree as it first should be hot to even allow nuclear fusion to happen.
The only assumption why it's that hot is in my opinion: There's huge, huge gravity of hydrogens and the biggest gravity are in the center as every element tries to get to the center. Hence, this means it's much dense in the core that anywhere else in the sun. Due to huge density, we got high pressure there. Density + Pressure must be causing the elements to have very high kinetic energy which is why the temperature is very high.
I might be wrong, but would be great if you could shed some lights on it.