Stellar Evolution

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Stellar Evolution

• The life-cycle of stars

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Star Energy

• Nuclear Fusion a nuclear reaction in which to
  atoms are fused together
• New elements are created and energy is released.
• This process is responsible for creating ALL
  elements found in the universe
• in other words, we are all made from star dust.

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Star Energy (cont)

• Hydrogen fusion
• H H ? He
• Helium fusion
• He He ? Be
• As the mass of elements increases, energy
  production increases

Energy
More Energy
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1. Nebula

• A cloud of gas and dust
• Gravity causes the cloud to collapse and condense
  
• Temperatures begin to increase Glows
• Fusion begins at VERY high temps.

(Some of the extra gas and dust may form planets)
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Main Sequence Stars

• Core reaches a temp of 15 million K.
• Hydrogen begins to fuse into Helium in the core.
  
• 90 of stars lifetime is spent in the main
  sequence stage.

• Classified based on temperature and luminosity

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Giant Stars

• Core decreases in size as
• All (or most) H is consumed
• He fusion is occurring producing more energy
• Diameter increases x10
• Surface temp decreases as star expands

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Super Giants

• Form from massive stars
• A chain of reactions take place in the core
  producing He, C, O, Ne, Mg, Si, S, Ar, Ca, Ti,
  Cr, Fe
• Highest temperature Blue Super Giants
• Usually explode in a tremendous event called a
  supernova

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Nova/Super Nova

• The core of a giant star produces too much energy
  in its core and causes the outside of the star
  to expand.
• The outer layer of gasses are blown out to space
  (nova, or supernova), leaving behind a small, hot
  core

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White Dwarf

• Stars decrease in size same diameter as earth,
  mass stays the same
• Mass of sun, size of Earth
• DENSITY INCREASES TREMENDOUSLY
• D 1,000,000 g/cm3
• 1 sugar cube gt 1 car
• Solid, but still hot, so it is glowing
• Luminosity decreases

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Neutron stars

• Form from the remains of extremely massive stars
  after a supernova.
• Very small 30 km across
• D 2 x 1014
• 1 sugar cube mass of humanity

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The fate of our Sun
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