The innermost layer of the Sun is called the core. The core is the central region of the Sun where nuclear fusion occurs, converting hydrogen nuclei into helium and releasing a tremendous amount of energy in the process. It is the hottest and densest part of the Sun, with temperatures reaching around 15 million degrees Celsius (27 million degrees Fahrenheit) and pressures millions of times greater than Earth's atmospheric pressure.
The core is where the immense gravitational pressure generated by the Sun's mass enables the fusion reactions to take place. The energy produced in the core is in the form of high-energy photons, primarily gamma rays, which then gradually make their way outward through the Sun's other layers, undergoing a series of interactions and transformations.
Surrounding the core, there are additional layers of the Sun, including the radiative zone, where energy is transported outward through the absorption and re-emission of photons, and the convective zone, where energy is transferred by large-scale convection currents. Above these layers lies the photosphere, which is the visible surface of the Sun that emits light and forms the boundary between the Sun and its outer atmosphere.
While the core is the innermost layer of the Sun, it is important to note that the Sun is a dynamic and complex structure with various layers and regions that play crucial roles in its overall behavior and energy production.