Lifecycle of A Star


Lifecycle of A Star

             Stars are such astronomical bodies which spontaneously emits light and heat. There is 70% Hydrogen, 28% Helium, 1.5% Carbon and 0.5% Neon and Nitrogen in a star. We can classify stars by their colours, size and brightness. Generally, there are three colours of stars- red white and blue. Colours show the temperature of a star. White colour shows a high temperature while the blue colour shows a high temperature of a star.



Origin of a Protostar: The life of a star starts in galaxy by condensation of Hydrogen and Helium. This gas transforms in cloud which have temperature of about -1730C. As these clouds become greater, their gravity becomes higher. When the size the size of a cloud becomes high enough, it stars contract itself. This body is called a protostar which does not emits light.

Formation of a Star from Protostar: Protostar is very dense body which continues contracting because of high gravity. In this continuous process, the hydrogen atoms of protostar collide with each other. So the temperature increases itself. This process continues for almost lakhs of years. Temperature of the star gets higher and reaches at 107 oC during this process. The fusion reactions of Hydrogen take place at this temperature. Helium atoms are made from these reactions. High energy is also produced with Helium which makes the tar bright.


Final stages of a star’s life-
Red-Giant Phase: When whole Hydrogen in crode is transformed in Helium by fusion. The pressure in crode becomes much less and the star starts contracting under its own gravity. Yet some hydrogen is left in outer layer of star which starts reactions and emits light. But this emission of light is too slow. The outer layer of star starts expanding and the crode starts contracting for balance. This state of star is called Red-Giant star. The red-giant star is an unstable state. Our sun will change into red-giant star after about 5000 million years.

            If a start’s mass is less than the Chandrashekhar limit [1.44 times of mass of the sun], it will eventually stop contracting and settle down in a stable final state as a ‘white dwarf’ with a radius of few thousand miles and density of hundred tons per cubic inch. A white dwarf is supported by the exclusion principle between the electrons in its matter. We have observed a large number of these white dwarf stars. One of the first to be discovered is a star that is orbiting around Cirius (The brightest star in the sky).
           
             A scientist, Landau pointed out another possible final state for a star, also with limiting mass of about one or two times the mass of the sun but much smaller even than a white dwarf. These stars would be supported by the exclusion principle repulsion between neutrons and protons, rather between electrons. They are therefore called neutron stars. They would have a radius of only 10 miles and density of hundred million tons per cubic inch. At the time they were first predicted, there was no way that neutron star could be observed. They were not actually detected until much later.





Black Holes: The fate of neutron star depends on its mass. According to the scientists, the contraction of neutron stars takes place for infinite time which eventually converts into black hole. Black holes have infinite gravity. Even light can’t come out of the black hole. So, none can see it. We can only notice its effect on nearly bodies.

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