Transcript ASTR 1101-001 Spring 2008 - Louisiana State University

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!