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ASTR 1102-002 2008 Fall Semester Joel E. Tohline, Alumni Professor Office: 247 Nicholson Hall [Slides from Lecture12] Chapter 20: Stellar Evolution: The Deaths of Stars Main Sequence (MS) Stellar Masses along the MS Masses obtained from Fig. 17-21 and Table 19-1 Low-, Moderately Low-, & HighMass Stars along the MS Terminology used throughout Chapter 20 Main-sequence Lifetimes Lifetimes obtained from Table 19-1 Low-, Moderately Low-, & HighMass Stars along the MS Terminology used throughout Chapter 20 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! 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! 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! 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! 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! Low-, Moderately Low-, & HighMass Stars along the MS Terminology used throughout Chapter 20 Main-sequence Lifetimes Lifetimes obtained from Table 19-1 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” 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” 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” 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” 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” Structure of an AGB Star 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” Planetary Nebulae (PN) PN “Abell 39” Figure 20-6b Planetary Nebulae (PN) Infrared Image of PN “NGC 7027” Figure 20-6c Planetary Nebulae (PN) A planetary nebula located inside globular cluster M15 Figure 20-6a Planetary Nebulae (PN) • For more images of various planetary nebulae, see – http://hubblesite.org/gallery/album/nebula_collection/ AGB PN white dwarf 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” AGB PN white dwarf Low-, Moderately Low-, & HighMass Stars along the MS Terminology used throughout Chapter 20 Main-sequence Lifetimes Lifetimes obtained from Table 19-1 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 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 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 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 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 Figure 20-13 “Onion-skin” Structure of High-mass Star’s Core 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 ironnickel group into heavier elements is a disaster! 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 ironnickel group into heavier elements is a disaster! 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 ironnickel group into heavier elements proves to be a disaster!