Download 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 Lecture13]
Chapter 20: Stellar Evolution:
The Deaths of Stars
and
Chapter 21: Neutron Stars
Low-, Moderately Low-, & HighMass Stars along the MS
Terminology used throughout Chapter 20
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
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
Comments (pt. 1)
• Before moving on to discuss the fate of highmass stars, a few comments about Planetary
Nebulae and White Dwarfs are in order.
– The shell of gas that is visible in each planetary
nebula illustrates that stars have a way of returning
material to the interstellar medium that has
undergone nuclear processing.
– Over time, the hot “central star” of a PN cools to
become a white dwarf:
• Approximately 1 M⊙ of material squeezed into a spherical
ball the size of the Earth!
• Density of material about 1 million times the density of water
Comments (pt. 1)
• Before moving on to discuss the fate of highmass stars, a few comments about Planetary
Nebulae and White Dwarfs are in order.
– The shell of gas that is visible in each planetary
nebula illustrates that stars have a way of returning
material to the interstellar medium that has
undergone nuclear processing.
– Over time, the hot “central star” of a PN cools to
become a white dwarf:
• Approximately 1 M⊙ of material squeezed into a spherical
ball the size of the Earth!
• Density of material about 1 million times the density of water
Comments (pt. 1)
• Before moving on to discuss the fate of highmass stars, a few comments about Planetary
Nebulae and White Dwarfs are in order.
– The shell of gas that is visible in each planetary
nebula illustrates that stars have a way of returning
material to the interstellar medium that has
undergone nuclear processing.
– Over time, the hot “central star” of a PN cools to
become a white dwarf:
• Approximately 1 M⊙ of material squeezed into a spherical
ball the size of the Earth!
• Density of material about 1 million times the density of water
Comments (pt. 1)
• Before moving on to discuss the fate of highmass stars, a few comments about Planetary
Nebulae and White Dwarfs are in order.
– The shell of gas that is visible in each planetary
nebula illustrates that stars have a way of returning
material to the interstellar medium that has
undergone nuclear processing.
– Over time, the hot “central star” of a PN cools to
become a white dwarf:
• Approximately 1 M⊙ of material squeezed into a spherical
ball the size of the Earth!
• Density of material about 1 million times the density of water
Comments (pt. 1)
• Before moving on to discuss the fate of highmass stars, a few comments about Planetary
Nebulae and White Dwarfs are in order.
– The shell of gas that is visible in each planetary
nebula illustrates that stars have a way of returning
material to the interstellar medium that has
undergone nuclear processing.
– Over time, the hot “central star” of a PN cools to
become a white dwarf:
• Approximately 1 M⊙ of material squeezed into a spherical
ball the size of the Earth!
• Density of material about 1 million times the density of water
Comments (pt. 2)
– As a WD continues to cool, gravity usually is unable
to squeeze it into an even smaller volume because of
“electron degeneracy pressure,” which …
• (distinct from ordinary gas pressure) arises due to the
quantum-mechanical nature of matter;
• can resist further gravitational compression even if the gas
temperature falls to zero!
– S. Chandrasekhar showed, however, that degeneracy
pressure is unable to beat the force of gravity if a
white dwarf has a mass greater than 1.4 M⊙
[Chandrasekhar mass = 1.4 M⊙]
Comments (pt. 2)
– As a WD continues to cool, gravity usually is unable
to squeeze it into an even smaller volume because of
“electron degeneracy pressure,” which …
• (distinct from ordinary gas pressure) arises due to the
quantum-mechanical nature of matter;
• can resist further gravitational compression even if the gas
temperature falls to zero!
– S. Chandrasekhar showed, however, that degeneracy
pressure is unable to beat the force of gravity if a
white dwarf has a mass greater than 1.4 M⊙
[Chandrasekhar mass = 1.4 M⊙]
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!
Excerpt from §21-1
On the morning of July 4, 1054, Yang Wei-T’e
(imperial astronomer to the Chinese court) made
a startling discovery. Just a few minutes before
sunrise, a new and dazzling object ascended
above the eastern horizon.
This “guest star” was so brilliant that it could easily
be seen during broad daylight for the rest of
July!
This “guest star” was visible in the night sky (to the
naked eye) for 21 months.
Excerpt from §21-1
On the morning of July 4, 1054, Yang Wei-T’e
(imperial astronomer to the Chinese court) made
a startling discovery. Just a few minutes before
sunrise, a new and dazzling object ascended
above the eastern horizon.
This “guest star” was so brilliant that it could easily
be seen during broad daylight for the rest of
July!
This “guest star” was visible in the night sky (to the
naked eye) for 21 months.
Excerpt from §21-1
On the morning of July 4, 1054, Yang Wei-T’e
(imperial astronomer to the Chinese court) made
a startling discovery. Just a few minutes before
sunrise, a new and dazzling object ascended
above the eastern horizon.
This “guest star” was so brilliant that it could easily
be seen during broad daylight for the rest of
July!
This “guest star” was visible in the night sky (to the
naked eye) for 21 months.
Crab Nebula
Today, if we look at the location on the sky where
Yang Wei-T’e discovered his “guest star” nearly
1000 years ago, we see a glowing gaseous
nebula that we call the “Crab Nebula”:
– The gaseous debris is expanding away from
its center at a rapid rate;
– projecting this expansion rate backward in
time, we conclude that the nebula originated
from a “point-like explosion” approximately
1000 years ago
Crab Nebula
Crab Nebula
Today, if we look at the location on the sky where
Yang Wei-T’e discovered his “guest star” nearly
1000 years ago, we see a glowing gaseous
nebula that we call the “Crab Nebula”:
– The gaseous debris is expanding away from its center
at a rapid rate;
– projecting this expansion rate backward in time, we
conclude that the nebula originated from a “point-like
explosion” approximately 1000 years ago
Crab Nebula
• At the center of the crab nebula, astronomers
have identified a peculiar, compact star (a
“pulsar”) that …
– At visible wavelengths is difficult to see;
– At radio wavelengths is a powerful “light-house”
beacon that flashes on and off 33 times every second!
Crab Nebula
• Astronomers are convinced that the gas making
up the Crab Nebula is (what is left of) the
outermost layers of a massive star that died
violently (a “supernova explosion”) in the year
1054, and that its central pulsar is a rapidly
rotating neutron star – a compact stellar
remnant, which was once the “core” of the highly
evolved, massive star.
• This illustrates how massive stars die!
Crab Nebula
• Astronomers are convinced that the gas making
up the Crab Nebula is (what is left of) the
outermost layers of a massive star that died
violently (a “supernova explosion”) in the year
1054, and that its central pulsar is a rapidly
rotating neutron star – a compact stellar
remnant, which was once the “core” of the highly
evolved, massive star.
• This illustrates how massive stars die! The
“disaster” alluded to earlier results in an
explosion of cataclysmic proportion.
Analogy Between SNe and PNe
• The outer layers of …
– moderately-low-mass stars are ejected (nonviolently)
to form a planetary nebula;
– high-mass stars are ejected explosively to form a
gaseous supernova remnant.
• The compact stellar remnant that remains is …
– A white dwarf, if the MS star is moderately low-mass;
– A neutron star, if the MS star is high-mass
• Maximum mass of compact stellar remnant is …
– 1.4 M⊙(Chandraskhar mass) for a white dwarf;
– Approximately 3 M⊙ for a neutron star.
Analogy Between SNe and PNe
• The outer layers of …
– moderately-low-mass stars are ejected (nonviolently)
to form a planetary nebula;
– high-mass stars are ejected explosively to form a
gaseous supernova remnant.
• The compact stellar remnant that remains is …
– A white dwarf, if the MS star is moderately low-mass;
– A neutron star, if the MS star is high-mass
• Maximum mass of compact stellar remnant is …
– 1.4 M⊙(Chandraskhar mass) for a white dwarf;
– Approximately 3 M⊙ for a neutron star.
Analogy Between SNe and PNe
• The outer layers of …
– moderately-low-mass stars are ejected (nonviolently)
to form a planetary nebula;
– high-mass stars are ejected explosively to form a
gaseous supernova remnant.
• The compact stellar remnant that remains is …
– A white dwarf, if the MS star is moderately low-mass;
– A neutron star, if the MS star is high-mass
• Maximum mass of compact stellar remnant is …
– 1.4 M⊙(Chandraskhar mass) for a white dwarf;
– Approximately 3 M⊙ for a neutron star.
Summary of Stellar Evolution
Supernovae
• Easily (and now frequently) detected in other
galaxies. (Statistically, every galaxy should
display 1-3 supernovae every 100 yrs.)
• The light display from each SN generally can be
categorized as one of several standard “types”:
– Type Ia
– Type Ib, Ic
– Type II
Supernovae
• Easily (and now frequently) detected in other
galaxies. (Statistically, every galaxy should
display 1-3 supernovae every 100 yrs.)
• The light display from each SN generally can be
categorized as one of several standard “types”:
– Type Ia
– Type Ib, Ic
– Type II
What About SNe in Our Galaxy?
• We’ve already discussed the Crab SN, which
exploded in 1054; our distance from the Crab
nebula is about 2000 parsecs, and it is
approximately 4 pc in diameter.
• Over the past 1000 years, written records
indicate that only 5 SN explosions have been
seen (by humans) in our “Milky Way” Galaxy
– Years 1006, 1054 (Crab), 1181, 1572, 1604
• We’re overdue!
• NOTE: Well over a thousand (!) pulsars have
been catalogued in our Milky Way Galaxy.
What About SNe in Our Galaxy?
• We’ve already discussed the Crab SN, which exploded
in 1054; our distance from the Crab nebula is about 2000
parsecs, and it is approximately 4 pc in diameter.
• Over the past 1000 years, written records indicate that
only 5 SN explosions have been seen (by humans) in
our “Milky Way” Galaxy
– Years 1006, 1054 (Crab), 1181, 1572, 1604
• We’re overdue!
• NOTE:
– Dozens of gaseous SN remnants are identifiable in our Galaxy
– Well over a thousand (!) pulsars have been catalogued in our
Galaxy.
What About SNe in Our Galaxy?
• We’ve already discussed the Crab SN, which exploded
in 1054; our distance from the Crab nebula is about 2000
parsecs, and it is approximately 4 pc in diameter.
• Over the past 1000 years, written records indicate that
only 5 SN explosions have been seen (by humans) in
our “Milky Way” Galaxy
– Years 1006, 1054 (Crab), 1181, 1572, 1604
• We’re overdue!
• NOTE:
– Dozens of gaseous SN remnants are identifiable in our Galaxy
– Well over a thousand (!) pulsars have been catalogued in our
Galaxy.
What About SNe in Our Galaxy?
• We’ve already discussed the Crab SN, which exploded
in 1054; our distance from the Crab nebula is about 2000
parsecs, and it is approximately 4 pc in diameter.
• Over the past 1000 years, written records indicate that
only 5 SN explosions have been seen (by humans) in
our “Milky Way” Galaxy
– Years 1006, 1054 (Crab), 1181, 1572, 1604
• We’re overdue!
• NOTE:
– Dozens of gaseous SN remnants are identifiable in our Galaxy
– Well over a thousand (!) pulsars have been catalogued in our
Galaxy.
What About SNe in Our Galaxy?
• We’ve already discussed the Crab SN, which exploded
in 1054; our distance from the Crab nebula is about 2000
parsecs, and it is approximately 4 pc in diameter.
• Over the past 1000 years, written records indicate that
only 5 SN explosions have been seen (by humans) in
our “Milky Way” Galaxy
– Years 1006, 1054 (Crab), 1181, 1572, 1604
• We’re overdue!
• NOTE:
– Dozens of gaseous SN remnants are identifiable in our Galaxy
– Well over a thousand (!) pulsars have been catalogued in our
Galaxy.
SN 1987A