ASTR 1102-002 2008 Fall Semester

1. ASTR 1102-0022008 Fall Semester Joel E. Tohline, Alumni Professor Office: 247 Nicholson Hall [Slides from Lecture12]

2. Chapter 20: Stellar Evolution:The Deaths of Stars

3. Main Sequence (MS)

4. Stellar Masses along the MS Masses obtained from Fig. 17-21 and Table 19-1

5. Low-, Moderately Low-, & High-Mass Stars along the MS Terminology used throughout Chapter 20

6. Main-sequence Lifetimes Lifetimes obtained from Table 19-1

7. Low-, Moderately Low-, & High-Mass Stars along the MS Terminology used throughout Chapter 20

8. Summary of Evolution • Low-Mass, “red dwarf” Stars (0.08 Msun£ M*£ 0.4 Msun) • Never leaves the main sequence • Fully convective all of the star’s hydrogen is eventually brought into the core for “burning” • Over hundreds of billions of years, evolves into an inert ball of helium • Boring!

9. Summary of Evolution • Low-Mass, “red dwarf” Stars (0.08 Msun£ M*£ 0.4 Msun) • Never leaves the main sequence • Fully convective all of the star’s hydrogen is eventually brought into the core for “burning” • Over hundreds of billions of years, evolves into an inert ball of helium • Boring!

10. Summary of Evolution • Low-Mass, “red dwarf” Stars (0.08 Msun£ M*£ 0.4 Msun) • Never leaves the main sequence • Fully convective all of the star’s hydrogen is eventually brought into the core for “burning” • Over hundreds of billions of years, evolves into an inert ball of helium • Boring!

11. Summary of Evolution • Low-Mass, “red dwarf” Stars (0.08 Msun£ M*£ 0.4 Msun) • Never leaves the main sequence • Fully convective all of the star’s hydrogen is eventually brought into the core for “burning” • Over hundreds of billions of years, evolves into an inert ball of helium • Boring!

12. Summary of Evolution • Low-Mass, “red dwarf” Stars (0.08 Msun£ M*£ 0.4 Msun) • Never leaves the main sequence • Fully convective all of the star’s hydrogen is eventually brought into the core for “burning” • Over hundreds of billions of years, evolves into an inert ball of helium • Boring!

13. Low-, Moderately Low-, & High-Mass Stars along the MS Terminology used throughout Chapter 20

14. Main-sequence Lifetimes Lifetimes obtained from Table 19-1

15. Summary of Evolution • Moderately Low-Mass Stars (like the Sun) (0.4 Msun£ M*£ 4 Msun) • Helium may ignite via a “helium flash” • In red-giant phase, core helium fusion converts helium into carbon & oxygen; hydrogen fusion continues in a surrounding shell • After core no longer contains helium, star may enter “asymptotic giant branch (AGB)” phase; helium continues to burn in a shell that surrounds an inert C & O core • As AGB star, star’s radius is 1 AU or larger! • Outer envelope ejected (nonviolently) to reveal the hot, inner core  planetary nebula • This remnant core cools to become a “white dwarf”

16. Summary of Evolution • Moderately Low-Mass Stars (like the Sun) (0.4 Msun£ M*£ 4 Msun) • Helium may ignite via a “helium flash” • In red-giant phase, core helium fusion converts helium into carbon & oxygen; hydrogen fusion continues in a surrounding shell • After core no longer contains helium, star may enter “asymptotic giant branch (AGB)” phase; helium continues to burn in a shell that surrounds an inert C & O core • As AGB star, star’s radius is 1 AU or larger! • Outer envelope ejected (nonviolently) to reveal the hot, inner core  planetary nebula • This remnant core cools to become a “white dwarf”

17. Summary of Evolution • Moderately Low-Mass Stars (like the Sun) (0.4 Msun£ M*£ 4 Msun) • Helium may ignite via a “helium flash” • In red-giant phase, core helium fusion converts helium into carbon & oxygen; hydrogen fusion continues in a surrounding shell • After core no longer contains helium, star may enter “asymptotic giant branch (AGB)” phase; helium continues to burn in a shell that surrounds an inert C & O core • As AGB star, star’s radius is 1 AU or larger! • Outer envelope ejected (nonviolently) to reveal the hot, inner core  planetary nebula • This remnant core cools to become a “white dwarf”

18. Summary of Evolution • Moderately Low-Mass Stars (like the Sun) (0.4 Msun£ M*£ 4 Msun) • Helium may ignite via a “helium flash” • In red-giant phase, core helium fusion converts helium into carbon & oxygen; hydrogen fusion continues in a surrounding shell • After core no longer contains helium, star may enter “asymptotic giant branch (AGB)” phase; helium continues to burn in a shell that surrounds an inert C & O core • As AGB star, star’s radius is 1 AU or larger! • Outer envelope ejected (nonviolently) to reveal the hot, inner core  planetary nebula • This remnant core cools to become a “white dwarf”

19. Summary of Evolution • Moderately Low-Mass Stars (like the Sun) (0.4 Msun£ M*£ 4 Msun) • Helium may ignite via a “helium flash” • In red-giant phase, core helium fusion converts helium into carbon & oxygen; hydrogen fusion continues in a surrounding shell • After core no longer contains helium, star may enter “asymptotic giant branch (AGB)” phase; helium continues to burn in a shell that surrounds an inert C & O core • As AGB star, star’s radius is 1 AU or larger! • Outer envelope ejected (nonviolently) to reveal the hot, inner core  planetary nebula • This remnant core cools to become a “white dwarf”

20. Structure of an AGB Star

21. Summary of Evolution • Moderately Low-Mass Stars (like the Sun) (0.4 Msun£ M*£ 4 Msun) • Helium may ignite via a “helium flash” • In red-giant phase, core helium fusion converts helium into carbon & oxygen; hydrogen fusion continues in a surrounding shell • After core no longer contains helium, star may enter “asymptotic giant branch (AGB)” phase; helium continues to burn in a shell that surrounds an inert C & O core • As AGB star, star’s radius is 1 AU or larger! • Outer envelope ejected (nonviolently) to reveal the hot, inner core  planetary nebula • This remnant core cools to become a “white dwarf”

22. Planetary Nebulae (PN) PN “Abell 39” Figure 20-6b

23. Planetary Nebulae (PN) Infrared Image of PN “NGC 7027” Figure 20-6c

24. Planetary Nebulae (PN) A planetary nebula located inside globular cluster M15 Figure 20-6a

25. Planetary Nebulae (PN) • For more images of various planetary nebulae, see • http://hubblesite.org/gallery/album/nebula_collection/

26. AGB  PN  white dwarf

27. Summary of Evolution • Moderately Low-Mass Stars (like the Sun) (0.4 Msun£ M*£ 4 Msun) • Helium may ignite via a “helium flash” • In red-giant phase, core helium fusion converts helium into carbon & oxygen; hydrogen fusion continues in a surrounding shell • After core no longer contains helium, star may enter “asymptotic giant branch (AGB)” phase; helium continues to burn in a shell that surrounds an inert C & O core • As AGB star, star’s radius is 1 AU or larger! • Outer envelope ejected (nonviolently) to reveal the hot, inner core  planetary nebula • This remnant core cools to become a “white dwarf”

28. AGB  PN  white dwarf

30. Low-, Moderately Low-, & High-Mass Stars along the MS Terminology used throughout Chapter 20

31. Main-sequence Lifetimes Lifetimes obtained from Table 19-1

32. Summary of Evolution • High-Mass Stars (4 Msun£ M*) • Evolution begins as in lower-mass stars, through the fusion of He into C & O and into the “AGB” phase • But gravity is strong enough (because of the star’s larger mass) for succeeding stages of nuclear “burning” to be triggered • When the star exhausts a given variety of nuclear fuel in its core, the “ash” of the previous fusion stage is ignited • The star’s core develops an “onion skin” structure with various layers of burning shells separated by inert shells of various elements

33. Summary of Evolution • High-Mass Stars (4 Msun£ M*) • Evolution begins as in lower-mass stars, through the fusion of He into C & O and into the “AGB” phase • But gravity is strong enough (because of the star’s larger mass) for succeeding stages of nuclear “burning” to be triggered • When the star exhausts a given variety of nuclear fuel in its core, the “ash” of the previous fusion stage is ignited • The star’s core develops an “onion skin” structure with various layers of burning shells separated by inert shells of various elements

34. Summary of Evolution • High-Mass Stars (4 Msun£ M*) • Evolution begins as in lower-mass stars, through the fusion of He into C & O and into the “AGB” phase • But gravity is strong enough (because of the star’s larger mass) for succeeding stages of nuclear “burning” to be triggered • When the star exhausts a given variety of nuclear fuel in its core, the “ash” of the previous fusion stage is ignited • The star’s core develops an “onion skin” structure with various layers of burning shells separated by inert shells of various elements

35. Summary of Evolution • High-Mass Stars (4 Msun£ M*) • Evolution begins as in lower-mass stars, through the fusion of He into C & O and into the “AGB” phase • But gravity is strong enough (because of the star’s larger mass) for succeeding stages of nuclear “burning” to be triggered • When the star exhausts a given variety of nuclear fuel in its core, the “ash” of the previous fusion stage is ignited • The star’s core develops an “onion skin” structure with various layers of burning shells separated by inert shells of various elements

36. Summary of Evolution • High-Mass Stars (4 Msun£ M*) • Evolution begins as in lower-mass stars, through the fusion of He into C & O and into the “AGB” phase • But gravity is strong enough (because of the star’s larger mass) for succeeding stages of nuclear “burning” to be triggered • When the star exhausts a given variety of nuclear fuel in its core, the “ash” of the previous fusion stage is ignited • The star’s core develops an “onion skin” structure with various layers of burning shells separated by inert shells of various elements

37. “Onion-skin” Structure ofHigh-mass Star’s Core Figure 20-13

38. Summary of Evolution • High-Mass Stars (cont.) • Successive stages of nuclear fusion ignition proceed until elements in the “iron-nickel group” are formed • Any attempt by the star to fuse elements in the iron-nickel group into heavier elements is a disaster!

39. Summary of Evolution • High-Mass Stars (cont.) • Successive stages of nuclear fusion ignition proceed until elements in the “iron-nickel group” are formed • Any attempt by the star to fuse elements in the iron-nickel group into heavier elements is a disaster!

40. Summary of Evolution • High-Mass Stars (cont.) • Successive stages of nuclear fusion ignition proceed until elements in the “iron-nickel group” are formed • Any attempt by the star to fuse elements in the iron-nickel group into heavier elements proves to be a disaster!