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Announcements

Announcements. Exam 2 is scheduled for Thursday March 7. Tentatively will cover Chapters 3 – 5 and probably Chapter 6. Sample Questions are posted

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Announcements

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  1. Announcements • Exam 2 is scheduled for Thursday March 7. Tentatively will cover Chapters 3 – 5 and probably Chapter 6. Sample Questions are posted • Project topics are due before spring break (March 7). Decide on a topic and come talk to me about it. The topic can be anything of current cosmological interest.

  2. Life beyond the Main Sequence What happens when a star runs out of hydrogen fuel in its core?

  3. With no more hydrogen fusion occurring in the core, hydrogen fusion continues in a shell around the core

  4. Energy imbalance from shell hydrogen fusion creates a Red Giant

  5. Helium Fusion starts when core reaches 100,000,000° The higher temperature is needed to overcome the stronger electric repulsion between the nuclei

  6. Triple Alpha Helium Fusion

  7. Additional Fusion involving He Ash from Helium Fusion: Carbon & Oxygen

  8. Helium fusion begins differently for some stars The determining factor is whether or not the core becomes degenerate

  9. Normal versus degenerate electron energy levels

  10. Degeneracy • Electron energy levels crowded together almost continuous • All low energy levels are full Pauli Exclusion Principle • Only place for additional electrons to go is in high energy levels which means they must be moving at close to the speed of light • Adding more mass decreases the volume • Temperature is same everywhere

  11. Evolution on an H – R Diagram Helium Flash

  12. For low mass stars: a second red giant stage The second red giant phase begins when the helium fuel in the core is exhausted and core fusion once again stops

  13. Internal Structure of AGB star

  14. Convection in final stages dredges up products of earlier fusion and ejects it into space

  15. Thermal Pulses cause whole layers of a star to lift off

  16. Stars recycle most matter back out into the universe

  17. Planetary Nebulae form from low mass stars (<8Msun)

  18. In the end, only the cooling core is left: a white dwarf star X-ray Canis Major Visible

  19. Colored Card Questions ClassAction website Stellar Evolution module HR Evolutionary Track HR Movement Core Stages 1 Core Stages 2

  20. White dwarf stars are planetary size but stellar mass

  21. White Dwarf Stars are degenerate matter Chandrasekhar Limit 1.4 Msun

  22. The evolutionary path of white dwarf stars are cooling curves

  23. A white dwarf in a binary system can be revived to become a cataclysmic variable

  24. For stars with mass >8Msun Carbon fusion begins at 600,000,000°

  25. Carbon fusion produces Oxygen, Neon and Magnesium

  26. Higher fusion requires higher temperatures and takes less time

  27. Internal Structure becomes layered like an onion

  28. Once iron starts to form energy is no longer produced

  29. When the iron core reaches 1.4 solar masses the end comes swiftly

  30. The End: Photo-disintegration and Reverse Beta Decay

  31. Type IIa Supernova Watch Supernova videos

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