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Announcements

Announcements. Second hour exam is this Friday, October 8 We will have a review session on Wednesday Please send in questions for the review by e-mail or on paper Observing continues this week. Evolution of high mass stars. Evolution of high mass stars Determining the age of a star cluster

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Announcements

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  1. Announcements • Second hour exam is this Friday, October 8 • We will have a review session on Wednesday • Please send in questions for the review by e-mail or on paper • Observing continues this week

  2. Evolution of high mass stars • Evolution of high mass stars • Determining the age of a star cluster • Supernovae • Reading 19.4, 20.2 (pages 469-471)

  3. Higher mass protostars contract faster Hotter

  4. Higher mass stars spend less time on the main sequence

  5. Determining the age of a star cluster • Imagine we have a cluster of stars that were all formed at the same time, but have a variety of different masses • Using what we know about stellar evolution is there a way to determine the age of the star cluster?

  6. Turn-off point of cluster reveals age

  7. Higher mass stars do not have helium flash

  8. Nuclear burning continues past Helium 1. Hydrogen burning: 10 Myr 2. Helium burning: 1 Myr 3. Carbon burning: 1000 years 4. Neon burning: ~10 years 5. Oxygen burning: ~1 year 6. Silicon burning: ~1 day Finally builds up an inert Iron core

  9. Why does nuclear fusion stop at Iron?

  10. Core collapse • Iron core is degenerate • Core grows until it is too heavy to support itself • Core collapses, density increases, normal iron nuclei are converted into neutrons with the emission of neutrinos • Core collapse stops, neutron star is formed • Rest of the star collapses in on the core, but bounces off the new neutron star (also pushed outwards by the neutrinos)

  11. If I drop a ball, will it bounce higher than it began?

  12. Supernova explosion

  13. In 1987 a nearby supernova gave us a close-up look at the death of a massive star

  14. Neutrinos from SN1987A

  15. Where do the elements in your body come from? • Solar mass star produce elements up to Carbon and Oxygen – these are ejected into planetary nebula and then recycled into new stars and planets • Supernova produce all of the heavier elements • Elements up to Iron can be produced by fusion • Elements heavier than iron are produced by the neutrons and neutrinos interacting with nuclei

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