Short answers, pulled from the story.
The solar core has a temperature of 15 million kelvins at its center, making it the hottest region in the entire Solar System. Near the outer edge of the core, at about 19% of the solar radius, temperatures drop to around 10 million kelvins.
The solar core generates 99% of the Sun's fusion power. Fusion power density at the Sun's center is estimated at 276.5 watts per cubic meter, comparable in power density to an active compost heap, though the Sun's enormous volume makes its total output vast.
Two reactions convert hydrogen into helium in the solar core. The proton-proton chain reaction produces most of the Sun's energy, releasing 26.7 MeV per reaction. The CNO cycle, which involves carbon atoms as intermediaries, accounts for less than 10% of total solar energy output.
Photons from the solar core take approximately 170,000 years to travel through the radiative zone alone, due to constant scattering off free electrons. During that journey, each gamma-ray photon is converted into several million visible-light photons before eventually escaping the Sun's surface.
The solar core has a density of 150,000 kilograms per cubic meter at the Sun's center. At 19% of the solar radius, near the core boundary, density falls to about 40 grams per cubic centimeter, roughly 27% of the central value.
The solar core maintains a self-correcting equilibrium: if fusion accelerates, the core expands slightly, lowering density and slowing the reaction rate back down. If fusion slows, the core contracts, raising density and restoring the fusion rate. This mechanism keeps the Sun's output stable over short timescales.