THE STORY OF THE SUNLIGHT

Sunlight is a very important thing for our everyday life. Light is electromagnetic radiation that is composed of photons. Photon is a force (electromagnetic force) carrying elementary particle. Electromagnetic radiation is separated according to the energy of the photon also known as electromagnetic spectrum which is consist of radio, infrared, micro wave, visible light, ultra violate light, x-rays and gamma ray. Radio wave has the lowest frequency (low energy) and have higher wave-length and gamma ray has the high frequency (high energy) and predictably lower wave-length than others but humans can only see the visible light.

The biggest light source in our solar system is the Sun. The Sun is a stupendous and phenomenal astronomical object in our solar system and also other stars in our large expanding universe box. The Sun produces energy as light by a spectacular process known as nuclear fusion more specifically proton-proton fusion. The Sun and the other stars formed by giant and heavier gases. Neutron and proton are made up of quarks (subatomic particle). Protons plays a major role the nuclear fusion. These giant and heavier gases mostly have hydrogen-(1) (i.e. it has one proton in the nucleus). Heavy gases come closer and collapse due to their gravity. They start to become hotter due to collapsing of gases and this breaks the atoms of gas into single charged particle and creates plasma and also the star becomes denser and denser. When the core of a star reaches 10 million Kelvin (it looks higher but this temperature is not enough to make the fusion at high rate) the nuclear fusion starts. Lots of free protons move fast (actually at very very high velocity!) inside the core.

 Protons consist of two up quark (charge of two up quark = 2*(+2/3)) and one down quark (charge of one down quark = -1/3) and this gives the positive charge of +1 (because (+4/3) + (– 1/3) = +1) to the proton but neutron consist of two down quark and one up quark this gives the neutral ((+2/3) + ( – 2/3) = 0) to the neutron. These three quarks are strongly held by strong nuclear force (gluons). There is other important force known as weak nuclear force which is responsible for radioactive decay of subatomic particles and weak force carries W and Z bozons. Weak force is responsible for beta decay that the neutron changes into proton and proton changes into neutron. A free neutron easily changes into a proton but a free proton can’t easily change into a neutron. When the positron emission (a form of radioactive decay) takes place a proton changes into a neutron because proton interacts with other subatomic particles. This process is important for nuclear fusion but this is slow and random process. Proton and other proton will not attract with each other (like magnets unlike poles attract and like poles repel) and their repulsive force is high. Sometimes the protons are moving very fast due to extreme temperature and pressure by gravity inside the core of a star and proton’s repulsion cannot prevent them from colliding and quantum tunneling also helps in this process (probability waves of the proton). 

So when two proton collide with each other and one of the proton turns into a neutron because of radioactive decay and releases a positron and neutrino and this forms hydrogen-(2) (1 proton and 1 neutron in the nucleus) and also known as deuterium. When other proton collides with hydrogen-(2) then it forms helium-(3) (2 protons and 1 neutron). When two helium-(3) collide with each other then it forms a perfect combination of helium-(4) (2 protons and 2 neutrons). 

While this process takes place on the particles collide with each other due to extreme temperature, gravity and quantum tunneling in the final result the particles losses some of their mass during nuclear fusion but we can’t destroy mass then what happened to that mass? Is someone like Thanos snap his fingers with infinity stones to disappear that mass? Nahhh, the mass is converted into energy(E=mc^2) in the form of gamma rays(high energy photon), amazing isn’t it? 

But this energy is absorbed by other subatomic particle and converted into kinetic energy of that particle and re-emitted in lower energy (lower frequency photon) and this process continues till it reaches the surface of the star. So, the final result is the higher energy photon converted into lower energy photon mostly in the form of infrared, visible and Ultra Violate light. Even though the energy is small but there are tons and tons of particles(10^57) in the core and the Sun releases lots of energy each second. This is how the nuclear fusion in The Sun produces light on Earth.