As we all know, the sun produces energy via a fusion reaction. Which is 4 hydrogen atoms, forced to fuse under high pressure. This produces enormous amounts of energy and a helium atom. To make it clear, the energy produced by the fusion of just 4 hydrogen atoms could power the bulb in your room for almost 100 years. Pretty cool right? Now, what if I told you that the core of the sun fuses around 600 million tons of hydrogen every second. Yeah… mind-blowing.
Nothing is permanent. just like your past relationship, the Sun too will come to an end, that too a fiery one. Stars, the size of our sun, have an average life span of 10 billion years. Our sun is just 4.5 billion years old. Scientists predict that in another 5 billion years, the sun will exhaust all its hydrogen and turn into a white dwarf. You see, by the passing second, the sun is fusing a lot of hydrogen to produce helium or other heavy elements at the core. Elements heavier than hydrogen, condense, making the core, more compact. This results in an increase in pressure at the center of the sun.
Fusion reaction accelerates under high pressure at the core which results in more heat produced over time. Slowly the sun becomes brighter and hotter. What about the heated gasses? It expands, slowly increasing the size of the sun.
After about 3.5 billion years from now, the sun will become 40 percent brighter than what it is now. Needless to say, in that heat, even your math teacher won’t survive, who usually survives the worst of natural calamities. But this would be way worse. Oceans would boil off, life would be wiped from the surface of the earth and who knows earth might start looking like mars. A star fuses hydrogen to produce energy and increase in size while heavier elements condense and pull the outer layers of the sun via gravitational forces. You see both the expanding and contracting forces cancel each other and the star remains stable.
But when a star runs out of its fuel, the expanding force is gone and all the heavy elements formed from the fusion of hydrogen will come together and condense down with a huge crushing force. Every action has an equal and opposite reaction. The huge crushing force will be followed by an equally powerful explosion, known as a supernova.
Coming back to our sun, for a supernova to happen the star needs to be really big and heavy, at least 10 times the size of our sun. so yea no supernova for our solar system. When our sun runs out of its fuel, it will form the red giant and eject a lot of hot gasses and debris into space. Since the core is being heated by the massive compressive force, it will emit a lot of light making the hot gasses and debris visible. This is what we call a planetary nebula. From a distance, it’s a pretty beautiful sight.
Now that all the explosions are done with, the core of the sun will stabilize, forming a white dwarf which would almost be the size of the earth. Don’t let the size fool you, the temperature of the white dwarf would be around 100 thousand kelvin. Compare that to the surface of the sun which is about 5 thousand kelvin. The white dwarf phase of the sun is the last but the longest phase. Spanning over a quadrillion years, that is 15 zeros after 1. The white dwarf would slowly lose its energy, becoming dim. Finally, it would cool down and become an earth-sized dark ball of condensed matter also known as the black dwarf, officially marking the death of our sun.
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This whole process would bring about a lot of change in the dynamics of our solar system and probably would make it inhabitable. The red giant phase would have swallowed mercury, Venus, and probably earth too, destroying any remains of life on the planet. Surely, our generation would not witness these cataclysmic events and right now mankind is in no hurry to find another habitable planet.