The long-anticipated and widely discussed doomsday will come, but it is going to happen in approximately five billion years. The core of the Sun will run out of hydrogen by this time, and our celestial body will turn into a red giant. The star will then gradually turn into a white dwarf - the core of the Sun. Scientists from the University of Cambridge have recently presented the computer model of this process.
When scientists say that the Sun can explode, common people mostly take such forecasts as absurdity. However, the Sun is not eternal. The Universe is not stable at all, and any of its bodies, including stars, undergo evolutionary cycles that start with their birth and end with death.
The explosion of the Sun is not going to look like an instant blast. It will become the result of complicated and long processes. It may happen in remote future, when mankind will most likely leave planet Earth. Humans will either become extinct or find other planets to live on.
Usually, a star begins its evolution in the form of a cold low-density cloud of interstellar gas. The cloud gets compressed under the influence of its own gravitation and takes a spherical shape. During the process of compression, the gravitational power transforms into heat and the body begins to warm up. As soon as the temperature inside the body reaches 15-20 million kelvins, thermonuclear reactions begin to take place inside the sphere. The compression process stops, and the object becomes a star.
A star of medium weight, like our Sun, remains in the state of the hydrogen-helium cycle throughout its life. When it burns the entire stock of hydrogen fuel, and hydrogen inside the core of the star turns into helium, the thermonuclear combustion of the hydrogen mantle continues. The luminosity of the object continues to grow, its outer layers continue to expand, whereas the surface temperature decreases. The star grows 100 times its size, and becomes a red giant. The star remains in this phase for a much shorter period of time - several millions of years.
The helium core of the giant can no longer stand its own weight and begins to compress. If the object is massive enough, the growing temperature may trigger the transformation of helium into heavier elements - carbon, oxygen, silicon and iron. This period may last for billions of years for the stars of medium weight.
As long as helium combustion reactions are very sensitive to temperature, the star may begin to pulsate vehemently and turn into planetary Nebula. The bared core in the center of medium-weight stars (like our Sun) cools down and becomes a helium white dwarf, the diameter of which is comparable to that of the Earth. Since white dwarfs have no sources of energy, they get dark and invisible as they continue to cool down. More massive stars turn either into neutrons (pulsars) or black holes. The evolution of stars ends with the birth of supernovas.
The gravitational power of the Sun will decrease as the celestial body slowly loses its weight. As a result, the objects of the solar system may descend from their orbits. Most likely, many planets, including Earth, will be burnt during the stage of the red giant.
The processes, which the dying Sun will cause, will affect the hypothesized Oort cloud of comets which may lie nearly a light year from the Sun. It will take the Sun approximately 100,000 years to lose weight, which is a very short period of time from the point of view of astronomy. Scientists say that about 20 percent of comets of the Oort cloud will be discharged into interstellar space during this process. This phenomenon will most likely look like gigantic fireworks.
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