Stars

Yeah, I about thought that too.
But it was hard to fit that on that small picture

"Too hot for burning" isn't exactly the phrase you're looking for. Burning is generally a reaction of Carbon with Oxygen, with the result of product of Carbon Dioxiode, e.g. Methane + Oxygen, CH4 + 2 O2 -> CO2 + 2 H20. Point is, most of Sun's mass is Hydrogen and Helium, as it's fairly "cool" and young star. When it becomes hotter by aging, the fusion temperature will increase to that extent that it will create heavier elements, like Oxygen or Carbon, eventually Iron.

...and when they grow old they increase in size and explode to destroy everything within a light year. Imagine if we would die the same way, well we could just swallow a handgrenade in crowded bus...

more like a millon times the size of earth

Yeah you're right. For most stars actually.