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The lifecycle of stars

Do we really know about a star?

    Stars are heavenly bodies, which shine like our sun. Many shine brightly, the others have a dim glow. Some are red while others are blue. Stars are giant balls of gas made of hydrogen, bound together by their own force of gravity. The energy that makes them shine comes from a kind of power plant in their interior, where atomic nuclei of hydrogen atoms are fused together to form helium atoms. The stars do not live forever and ;die' at some point. Many simply get extinguished, while very heavy stars expand and explode. Their remains become either a neutron star of a 'black hole'.   The cradle of a star is a cloud of hydrogen and dust. There are numerous such clouds in the universe. By the action of external forces -such as the explosion of a star -this cloud gets compressed and keeps pulling itself together due to the increasing force of attraction among the particles. After a few hundreds of thousands of years, it begins to shine. A proto-star, a star in the early stages, is formed. This keeps pulling itself together while rotating, and becomes hotter and hotter, till its interior reaches a temperature of around 10 million degrees Celsius. In the core of the star, the fusion of hydrogen into helium releases an enormous amount of energy. Now, the star becomes a main sequence star. It shines approximately for 10 billion years, till it 'dies'.



All stars not shine with the same intensity.

   There are two reason why all the stars in the night sky do not shine equally brightly. Firstly, the stars are at different distances from the Earth. Secondly, their luminosity depends on their age. Young stars are bright, hot and shine bluish-white, and older stars which have already given out a lot of their energy are red in colour and are cooler. Our sun is middle aged (about 4.8 billion years old), with a temperature of around 5500°C on its surface, and a yellow shine. Stars are like a window to the past. If a star is 10 years to reach us. Consequently, we see the star not as it is 'now', but as it was 10 years ago.

Last stage of a star

When the fusion of hydrogen into helium takes place in the core of star, it continues to shine for about 10 billion years. At some point of time, however, all the hydrogen gets consumed. Helium then melts to form carbon. What happens after this depends on the mass of the star. Lighter stars like the sun expand to become a red giant, till the fusion stops, and then implode to become a white mass about the size of the Earth. Very large stars, about 20 times heavier than out sun, expand to become a giant and finally explode. This is known as 'supernova'. The remains of a supernova become either a neutron star or a black hole.


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