star formation

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Clint Wolf, Sep 17, 2001.

  1. Clint Wolf Registered Member

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    As we know, all of the hydrogen that exists in the universe was created in the first 200 or so seconds. Quite a mind blowing thought. However, this reminds us that the quantity of hydrogen in the universe is finite, so the available hydrogen to be used in star formation must eventually be consumed. At this point, will stars begin forming and igniting from free helium (with helium being the first stage of combustion)?

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  3. Hevene Registered Senior Member

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    Star Evolution

    During the formation of the star, the gravitational potential energy is turned into heat. The temperature continues to rise until it reaches the main sequence and emits light. eg. out sun. The star has to reach stellar equilibrium (the balance of the gravity pulling the material in and the pressure of the plasma going outwards), this is done by an energy source at the core. For a main sequence star, hydrogen fusion does the job, called the proton-proton chain. Energy is released in the form of radiation. As the hydrogen is changed to helium, the core slowly turns to a helium core and collapse as there is no more energy formed in the core to held against the strong gravity. As it collapses, the gravitational energy is converted to heat energy, which allows the helium fusion to occur in the core. This cause the star to expands as extra heat is provided, and the star cools. Now the surface temperature decreased and the light emitted bacomes redder, now the star is a red giant. As the star consumes helium, eventually nuclear reaction stops. Smaller stars ejects planetary nebulae, leaving behind a white dwarf, bigger stars (greater than 8 soar masses) explode as supernovae, leaving hehind a sutron star and a black hole depend on the size. For star with initial mass greater than 8 solar masses, the nuclear fusion goes further. The helium core continues to react to form carbon and oxygen, which in turn produces element up to iron. When the iron core approaches the Chandrasekhar limit of 1.4 solar masses, there's no more energy left, the gravity causes the core to collapse. Due to the high density, the core resist furthur collapse and produes a core bounce. During this, large amount of energy is produced, and the star explodes. Iron is synthesised during this by neutron capture and these elements goes into the space for furure use.
     
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  5. wet1 Wanderer Registered Senior Member

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    Welcome to Sciforums, Clint Wolf.

    I think that Hevene did an exellent job with the explaination. I have nothing to add, nice work, Hevene.
     
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  7. Hevene Registered Senior Member

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    Thanks
     

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