The core of the sun extends from the center to about a quarter of the radius of the sun. Although it accounts for only 16 percent of the volume, about half of the sun's mass is concentrated here, at a temperature of about 15 million degrees Celsius and a pressure of several tens of billions of Hectopascals, the air pressure corresponding to about one Hectopascals.
Here, hydrogen nuclei fuse to form helium nuclei. These helium nuclei have a slightly smaller mass than the original hydrogen nuclei and it is this mass difference that is converted into energy according to Albert Einstein's theory of relativity and the famous formula E=mc².
In the core of the sun, 700 million tons of hydrogen are fused into 695 million tons of helium per second, and yet the core of the sun is actually too cold for nuclear fusion.
The kinetic energy of the particles is not sufficient to overcome the strong repulsive forces of the positively charged hydrogen nuclei in the event of a collision. The fact that the engine is still running is due to quantum mechanical tunnel effects. In this way, the hydrogen nuclei can overcome the electrical repulsion. The probability of this happening is low. But because an immense number of hydrogen nuclei are present, enormous amounts of energy can still be released.
This slowed down nuclear fusion is of crucial importance for the solar system and life on earth. Because the sun uses its energy reserves sparingly, it can radiate constant amounts of energy over a long period of time.
Around the core lies the so-called radiation zone, which accounts for about 70 percent of the sun's radius. This is where the radiation generated in the core is slowed down. Statistically, a photon, a light particle or light quantum takes 170 thousand years to pass through this radiation zone. The light that we receive today from the sun was created at a time when our ancestors still regarded the fist wedge as high-tech.
With every collision in the radiation zone, the radiation energy of the proton decreases and its wavelengths increase. Thus, the high-energy gamma radiation in the nucleus first becomes X-ray light, then UV radiation and finally visible light.
