The transfer of energy within stars - why aren’t we ‘zapped’ by harmful radiation?
In the core of every star the energy motion made from energy mass via nuclear fusion appears in the form of additional velocity acquired by each of the particles that energy from the nuclear fusion. Before the fusion, the particles had energy of motion since each of them was in motion. After the fusion the particles have more energy of motion, which they gained from the energy of mass that vanished during the fusion process.
What happens to the energy of motion of the particles that emerge from the fusion? The particles collide with particles immediately around them, which in turn collide with other particles, and they in turn collide with others still, until the newly fused particles share the energy of motion made at the star’s centre with the entire star.
Likewise, high-energy photons made during the nuclear fusion collide with other particles and increase the particles’ velocities. Eventually, like a mob animated by demagogue at its centre, all the particles within the star dance in a frenzy induced by the nuclear fusion at the stellar core. The particles dance most furiously at the star’s centre, progressively less so in the outer regions.
Thus, from nuclear fusion at its core the entire star grows hot from the centre to surface. The star’s centre typically has a temperature of 15 - 60 million degrees Fahrenheit, while the surface falls to a mere 2,000 - 25,000 degrees.
Because a star is hot it produces electromagnetic waves, in fact any object not at a temperature of 0 Kelvin (the coldest temperature possible) produces electromagnetic radiation, and these levels increase the hotter an object gets. Furthermore, as an object grows hotter the chief type of electromagnetic wave it radiates will chance. Human beings and other objects near room temperature produce mostly infrared waves. Hence, the sizable military industry that has sprung up to detect the infrared waves that humans emit in order to see the enemy simply by the waves that they cannot avoid radiating. At temperatures of a few thousand degrees, an object will emit mostly visible light. Stars, with surface temperatures measured in thousands of degrees therefore radiate mostly visible light, along with sizable amounts of ultraviolet from the hotter stars. Not accidently, our eyes have evolved to detect mostly visible light, the sun’s primary output.
In the core of a star such as the sun, where the temperature rises to millions of degrees, the hot gas radiates mostly X-rays and gamma rays. If the outer layers of the sun were transparent to this radiation we would be instantaneously zapped by these high energy photons from the solar interior. However, the matter in the sun effectively traps all this harmful radiation, each of the rays encountering a nucleus or an electron which blocks its path and deflects it in another direction. The high-energy photons therefore cannot escape from the sun; instead, their energy is constantly passed to other particles within the sun, heating them still further. The immense number of collision slowly lessens the energy of each photon, and if we could pass outward in the sun from its centre to its surface we would find mostly gamma rays and X rays near the core, mostly X rays and ultraviolet in its middle regions, and mostly ultraviolet and visible light near the surface. Finally from the regions close to the sun’s surface photons can escape, but because these regions have temperatures of only about 10,000 degrees Fahrenheit, the photons that do escape are ultraviolet and visible light photons, the kind that matter at this temperature produces.
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