The rate of fusion in the Suns core is actually very slow and gram for gram it is not producing much energy. But the core of the Sun is well insulated by the v

The rate of fusion in the Suns core is actually very slow and gram for gram it is not producing much energy. But the core of the Sun is well insulated by the vast bulk of itself, so even a slow release of energy builds up to extreme temperatures. https://en.wikipedia.org/wiki/Sun#Structure_and_fusion https://en.wikipedia.org/wiki/Sun#Structure_and_fusion