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Announcements: Exam #3: May 3 (Chp 12, 13)

Announcements: Exam #3: May 3 (Chp 12, 13). HR Diagram of the Brightest Stars. HR Diagram of the Closest Stars. Conclusions: Low mass stars are more common in our galaxy (not a lot of O and B-type Main Sequence Stars in the HR Diagram of the closest stars).

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Announcements: Exam #3: May 3 (Chp 12, 13)

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  1. Announcements: Exam #3: May 3 (Chp 12, 13)

  2. HR Diagram of the Brightest Stars

  3. HR Diagram of the Closest Stars

  4. Conclusions: • Low mass stars are more common in our galaxy (not a lot of O and B-type Main Sequence Stars in the HR Diagram of the closest stars). • Stars spend most of their time on the Main Sequence (not a lot of supergiants and giants in the HR Diagram of the closest stars).

  5. Chapter 13

  6. Introduction • Where do stars come from? • Giant Molecular Clouds • Bok Globules • Interstellar Medium (ISM) • Protostars • Pre-Main Sequence Stars • How do they age (evolve) • What is their fate?

  7. Bi-polar jets Herbig-Haro objects (HH objects) Brown Dwarfs Contraction timescales depend on mass Hydrostatic Equilibrium

  8. Sun becomes a Red Giant

  9. Planetary Nebulae: Typical size: 0.25 ly Typical velocity of expanding material: 20 km/s

  10. At the end of its life, a star like the Sun will shed its outer layers.

  11. Collapse of Massive Stars: • As the star’s core shrinks, protons and electrons merge to form neutrons and the core is transformed into a sphere of neutrons. p+ + e- n +  • The loss of electrons in the creation of the neutrons causes the core pressure to drop suddenly – nothing remains to support the star, so its inner layers collapse In a matter of seconds the Earth-sized iron core is transformed into a 10-km, extremely dense ball of neutrons

  12. Collapse of Massive Stars: • The outer layers of the star, now not supported as well, collapse and heat to billions of degrees as they slam into the neutron core. • The gas pressure surges and thrusts the outer layers back into space in a gigantic explosion – a supernova.

  13. Supernova Explosions: • In a few minutes, more energy is released than during the star’s entire life. • It brightens to several billion times the luminosity of the Sun – a rate larger than all the stars in the Milky Way combined. • Speeds may exceed 10,000 km/sec • Free neutrons from the explosion synthesize heavier elements (e.g., gold, platinum, uranium) • Materials mix with interstellar matter to be recycled into a new generation of stars

  14. NGC 4725 (late 1940’s)

  15. Large Magellanic Cloud: SN1987A

  16. Supernova Remnants (Vela, Crab)

  17. Crab Nebula: Noted by Chinese Astronomers in 1054 AD Constellation of Taurus 6000 LY away 6 LY across Expanding at 3 million MPH

  18. NGC 3603: 2 million years old

  19. Stars like the Sun probably do not form iron cores during their evolution because a) all of the iron is ejected when they become planetary nebulae b) their cores never get hot enough for them to make iron by nucleosynthesis c) the iron they make by nucleosynthesis is all fused into carbon d) their strong magnetic fields keep their iron in the atmosphere e) none of the above

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