Death of a Star

Universe is made up of many different elements. Stars are also one of the element of this Universe. As we know, if the sky is clear then we see many uncountable stars are twinkling at the night time. Have you ever noticed or had a knowledge that stars are born and also they die after certain interval of time. Now in your mind many questions have been raised such as Do the stars are really born? Do they really die? Do these things really happen? After reading this article you will know everything from the born upto death of Stars and afer that also what happens.

When a star is born, its hydrogen goes on being used in fusion. When the hydrogen fuel is exhausted, the outward pressure created by the nuclear reactions ceases and the gravitational force within the star predominates. The star goes on contracting. Due to the contraction, the core temperature rises which causes the expansion of the outer layers of the star. The expansion causes cooling effect. The result is that size of the star grows and the temperature falls. Ultimately, a stage is reached at which the star becomes very large in size and red in color and it is called Red giant. This red giant lasts for millions of years and at its end, the star begins emitting energy at tremendous rate for which the helium becomes the fuel. At the end, a violent explosion called nova/supernova occurs. Due to this explosion, large portion of the stars envelop is thrown into the interstellar space which ends the existence of the star and the star is dead.

 Now, there are three types of dead bodies of stars and they are:
 a. White dwarf
 b. Neutron star and
 c. Black hole

The red giant initially having mass less than 2 Ms (mass of the sun) cools to change its color from white to yellow, yellow to red and finally disappears and its mass becomes equal to that of the earth. This is known as White dwarf.

When the mass of the star is greater than 2 Ms and less than 5 Ms, contraction collide with protons to produce neutrons and eventually the stars becomes full of neutrons. This is known as Neutron star. It does not emit light, but sends out radio waves in the form of pulse. So they are also known as Pulsars. They have a diameter of about 10^-20 km, density 10^17 kg/m^3 and produce intense magnetic field of the order of 10^8 T.

The massive star having mass more than 5 Ms, undergoes uncontrolled contraction because of inward pull of its own gravity. The star becomes so dense that nothing even light can escape from its gravity. This is known as black hole. It is a very large amount of matter packed in a small area. Think of a star 12 times more massive than the sun which is squeezed into a sphere approximately the diameter of Kathmandu city. The result is a gravitational field which is so strong that nothing, even the light cannot escape through it.

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