Therefore, the sun gets old when the “fuel” inside the sun runs out. Scientists believe that the current age of the sun is about 4.57 billion years. During these long billions of years, the sun has converted 100 earth masses of matter into energy. Calculated at this rate, the hydrogen fuel inside the sun can last for about 5.4 billion years. When the sun gets old, the “hydrogen fuel” inside is basically “burned out”, leaving a core composed of helium. The helium core shrinks to resist gravity, and at the same time releases a large amount of heat energy. As a result, the inner layer of the sun is hotter, and the hydrogen wrapped in the outer layer of the helium core is “ignited” again. The release of these heat caused the volume of the sun to expand rapidly, and the sun at this time became a red giant star.
How scary is the red giant sun? First of all, the size becomes extremely large. Scientists estimate that the sun’s radius will expand to a maximum of 256 times its current size, and its volume will expand by a factor of 17 million. Now the radius of the sun is 696,000 kilometers, and its 256 times is about 178 million kilometers. The average radius from the earth to the sun is about 150 million kilometers. Obviously, when the sun becomes a red giant and expands to the maximum, the earth will be swallowed by the sun. Scientists expect this time point to occur about 7.6 billion years from now. Secondly, the sun will have a helium flash. After the sun becomes a red giant, when the temperature of the core reaches 100 million degrees Celsius, the helium element starts to burn to form carbon element. Since the sun no longer has enough mass, the internal helium fusion is a runaway thermonuclear fusion.
When a helium flash occurs on the sun, it will be found on the earth that the brightness of the sun suddenly increases by 100 to 10,000 times compared to the original. Accompanied by the sudden increase in brightness, the energy released by the helium flash in just a few seconds is equivalent to 100 billion times the energy normally released by the sun in the main sequence stage. At this time, the earth may be doomed. Scientists predict that the sun will undergo a helium flash 1.2 billion years after the end of the main sequence star phase, about 6.6 billion years later. Moreover, the helium flash of the sun will occur many times, and each helium flash will consume a large amount of helium, and after the helium flash, the helium produced by the “shell nuclear fusion” of the outer layer will continue to accumulate, and will occur when it reaches a certain level Next helium flash. In this way, the sun will die in one helium flash after another.
During this process, the outer layer of the sun will be thrown away in large quantities, forming a spectacular planetary nebula, and the inner layer will gradually form a dense white dwarf star, and the earth will no longer exist by then. However, this is only the outcome of the natural evolution in the universe, without taking into account the influence of humans. It may be optimistic that with the advancement of technology, future humans should be able to change the outcome of the earth and even the sun.
