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The star are self glowing heavenly bodies which generate the energy themselves by nuclear fusion reaction. The temperature of stars is very high. About 3000 stars can be seen in the skyinclearnight with naked eyes.The sun is the nearest star of earth. Alpha centauri is the nearest star of the sun.

Evolution of Stars:

  1. Formation of star:

    Scientist believed that stars are formed by the nebula. The nebula will make the collection of inter seller objects into various places into smaller parts. By any means, any one of the mass will develop the gravitational force and stars to attract the other patches towards itself. As a result of which its mass increases and the pressure on the circle also increases. And when the temperature of center reaches 5 x 106 degree Celsius then it is called a protostar .In protostar gradually nuclear fusion reaction starts, due to excessive gravitational force, and it converts into stars.

  2. Destruction of stars
    • Red giant:
      In stars, gravitation is pulling all matter to its core and that force is balanced by the repulsive force created by nuclear reaction in the core. When the stock of hydrogen starts to finish then gravitation starts to take over and compress the star. Due to high gravitational pressure helium starts to fuse to give carbon this release high amount of energy. Due to that energy stars expand their diameter. Red giants have the radius from 100 million to a billion kilometers. Since the surface area of the star increases the produced energy is distributed over large area. So the temperature of the star decreases. Our sun becomes red giant in about 5.5 billion years from now.
    • White dwarf:
      If the mass of red giant is smaller or equal to sun then gradually the outer part will start to escape into space, then the inner core which is still hot starts to seem white, which is called white dwarf.
    • Black dwarf:
      Gradually, the white dwarf continues to cool and finally it turns into black color which is called black dwarf. Finally, it starts to be invisible.
    • Supernova:
      If the red giant is extremely big, then in core, further fusion reaction will continue. Then the helium core turns into carbon, oxygen , neon, silicon and finally iron and finally core of star explodes and such exploding star is called the supernova.
    • Neutron star:
      Sometimes, after the supernova explosion, nothing of star is left, the central core of the star which is equal to the size of earth. In which the proton and electron fuse together to give neutral neutron is called neutron star.
    • Pulsar:
      A rapidly spinning neutron star surrounded by an extremely powerful magnetic field that can spin with it and is called pulsar.
    • Black hole:
      A black hole is a remnant of a star so condensed that it's gravitational pull is strong enough to prevent matter or even formed by identification contraction of heavy and large neutron stars under the action of their own gravity.



  • The star are self glowing heavenly bodies which generate the energy themselves by nuclear fusion reaction.
  • The temperature of star is very high.
  • About 3000 stars can be seen in the sky in clear night with naked eyes.
  • The sun is the nearest star of earth. Alpha centauri is the nearest star of the sun.
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Questions and Answers

Click on the questions below to reveal the answers

When hydrogen changes to helium (­4­1H12H4­) tremendous energy is released. This energy is used to keep stars shining. When hydrogen is finished, there is no more production of heat. When outside pressure decreases, the gravitational pull causes the star to contract. Due to contraction, the temperature of the outer core increases. This results in the expansion of the outer layers and increase in the size of the star. The expansion causes the temperature of the outer layers to fall and thus the stars becomes very large in size and red in color (also called, a red giant).

Black hole is an object with highest density and such a great force of gravity that can even attract light, that is, even light cannot come out of this object. When hydrogen gets exhausted, extremely large stars contract as a result of the gravity and protons and neutrons start to come together. The force of gravity become so large that even light cannot escape from it.

When hydrogen gas exhausted extremely large stars contract as a result of the gravity and protons and neutrons start to come together. The force of gravity becomes so large that even light cannot escape from it and it appears as a black hole.

At night some stars look brighter than the other. There are two factors that determine the brightness of any star- size and distance from the earth. Those stars that look brighter are either bigger stars or are closer to the earth. The closest star is the sun. That's why it is the brightest.

The stars contract continuously as hydrogen goes on decreasing. This results in the increase in temperature and pressure of the core. The surface heat and pressure decrease and the stars expand. These very large- sized stars that are red in color are called red giants.

The two specific characteristic of black hole are:

  1. Event Horizon is the area surrounding a black hole where the escape velocity is equal to the speed of light
  2. It does not allow even light to escape as it has a very high gravitational pull. 

The four differences between a star and a planet are:
Star Planet
  1. It has its own light.
  2. It twinkles as it emits light continuously.
  3. It is a very big mass of extremely hot gases.
  4. Star does not change its relative positions in the sky.
  1. It does not have its own light.
  2. It shines by reflecting the light it gets from the sun.
  3. It is generally a solid body made of rock and minerals.
  4. It changes its relative position in the sky.

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  • The giant family of sun including planets, asteroids , comets etc is called ______.

    constellation


    atmosphere


    galaxy


    solar system


  • The nearest star to the sun is ______.

    Alpha centauri


    Gamma centauri


    Delta centauri


    Beta centauri


  • Which is the largest satellite in our solar system?

    Phobos (Mars)


    Titan (Saturn)


    Moon (Earth)


    Ganymede (Jupiter)


  • The planet having shortest orbit is _______.

    Mercury


    Venus


    Saturn


    Neptune


  • What is a shooting star?

    space junk
    dying star
    comet
    Meteor
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ASK ANY QUESTION ON Stars


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Forum Time Replies Report
how many type of meteorite are there?


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samriddhi

what is neutron star?


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Avinab

In which condition does Thermo nuclear reaction takes place in star ?


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Avinab

HOW DOES THE RED GIANT FORM ?


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