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ASTRONOMY

ASTRONOMY. Chapter 27 The Birth, Youth, and Middle Age of Stars. Formation of Stars. Stellar evolution Born from a cloud of gas and dust A region becomes more dense Random density fluctuation Shock wave from a supernova Gravity attracts more gas and dust

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ASTRONOMY

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  1. ASTRONOMY Chapter 27 The Birth, Youth, and Middle Age of Stars

  2. Formation of Stars • Stellar evolution • Born from a cloud of gas and dust • A region becomes more dense • Random density fluctuation • Shock wave from a supernova • Gravity attracts more gas and dust • Energy from the contraction heats the gas • This protostar gives off electromagnetic radiation.

  3. Evolutionary Track • The life history of a star can be plotted on the H-R diagram. • Each point on the graph represents a particular moment in the star’s life.

  4. High Mass vs. Low Mass • High mass protostars will contract more quickly than lower mass protostars • What takes a 1 solar mass protostar 50 million years will only take a 10 solar mass protostar about 200,000 years.

  5. The Nuclear Furnace • As a star collapses, the gravitational potential energy of the gas particles is converted to heat. • The center of the star heats up and the pressure builds until conditions are right for nuclear fusion.

  6. Atoms • Atoms are made of protons, neutrons, and electrons. • Protons and neutrons are in the nucleus and electrons are located in the electron cloud. • The nucleus is about 1/10,000th the diameter of the atom. • Most of an atom is empty space. • When an atom gains or losses electrons, it is called an ion.

  7. Plasma • In a star, the hydrogen atoms lose their electrons and form plasma, the 4th state of matter. • This is why matter from a star is so dense. • In the center of a star, the hydrogen nuclei – protons – are very close together and moving very fast.

  8. Nuclear Fusion

  9. Nuclear Fusion • In the core of a star (generally): • Four hydrogen nuclei combine to make a helium nucleus. • A little mass is “lost”. • The “lost” mass is converted to energy according to the equation E=mc2. • A small amount of mass gives a huge amount of energy.

  10. Nuclear Fusion • The exact nuclear reaction is believed to depend on the core temperature of the star: • At 15 million K the proton-proton star chain dominates. (p 512) • Above 15 million K the carbon-nitrogen-oxygen cycle dominates. (p 513) • Above 108 K the triple alpha process occurs. (p 514)

  11. Nuclear Fusion • Once nuclear fusion starts, the outward thermal pressure will balance the inward force of gravity. • The star reaches hydrostatic equilibriumand settles into its place on the main sequence. • The star is now in the prime of its life.

  12. The End

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