ASTR%201102-002%202008%20Fall%20Semester

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ASTR 1102-0022008 Fall Semester

• Joel E. Tohline, Alumni Professor
• Office 247 Nicholson Hall
• Slides from Lecture13

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Chapter 20 Stellar EvolutionThe Deaths of
StarsandChapter 21 Neutron Stars
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Low-, Moderately Low-, High-Mass Stars along
the MS
Terminology used throughout Chapter 20
4
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, stars 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

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Structure of an AGB Star
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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, stars 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

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Planetary Nebulae (PN)
PN Abell 39
Figure 20-6b
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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, stars 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

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AGB ? PN ? white dwarf
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Comments (pt. 1)

• Before moving on to discuss the fate of high-mass
  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

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Comments (pt. 1)

• Before moving on to discuss the fate of high-mass
  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

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Comments (pt. 1)

• Before moving on to discuss the fate of high-mass
  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

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Comments (pt. 1)

• Before moving on to discuss the fate of high-mass
  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

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Comments (pt. 1)

• Before moving on to discuss the fate of high-mass
  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

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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?

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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?

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Low-, Moderately Low-, High-Mass Stars along
the MS
Terminology used throughout Chapter 20
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Main-sequence Lifetimes
Lifetimes obtained from Table 19-1
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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
  stars 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 stars core develops an onion skin
  structure with various layers of burning shells
  separated by inert shells of various elements

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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
  stars 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 stars core develops an onion skin
  structure with various layers of burning shells
  separated by inert shells of various elements

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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
  stars 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 stars core develops an onion skin
  structure with various layers of burning shells
  separated by inert shells of various elements

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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
  stars 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 stars core develops an onion skin
  structure with various layers of burning shells
  separated by inert shells of various elements

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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
  stars 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 stars core develops an onion skin
  structure with various layers of burning shells
  separated by inert shells of various elements

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Onion-skin Structure ofHigh-mass Stars Core
Figure 20-13
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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!

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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!

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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!

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Excerpt from 21-1

• On the morning of July 4, 1054, Yang Wei-Te
  (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.

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Excerpt from 21-1

• On the morning of July 4, 1054, Yang Wei-Te
  (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.

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Excerpt from 21-1

• On the morning of July 4, 1054, Yang Wei-Te
  (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.

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Crab Nebula

• Today, if we look at the location on the sky
  where Yang Wei-Te 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

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Crab Nebula
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Crab Nebula

• Today, if we look at the location on the sky
  where Yang Wei-Te 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

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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!

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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!

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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.

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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.

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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.

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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.

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Summary of Stellar Evolution
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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

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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

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What About SNe in Our Galaxy?

• Weve 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
• Were overdue!
• NOTE Well over a thousand (!) pulsars have been
  catalogued in our Milky Way Galaxy.

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What About SNe in Our Galaxy?

• Weve 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
• Were overdue!
• NOTE
• Dozens of gaseous SN remnants are identifiable in
  our Galaxy
• Well over a thousand (!) pulsars have been
  catalogued in our Galaxy.

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What About SNe in Our Galaxy?

• Weve 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
• Were overdue!
• NOTE
• Dozens of gaseous SN remnants are identifiable in
  our Galaxy
• Well over a thousand (!) pulsars have been
  catalogued in our Galaxy.

51
What About SNe in Our Galaxy?

• Weve 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
• Were overdue!
• NOTE
• Dozens of gaseous SN remnants are identifiable in
  our Galaxy
• Well over a thousand (!) pulsars have been
  catalogued in our Galaxy.

52
What About SNe in Our Galaxy?

• Weve 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
• Were overdue!
• NOTE
• Dozens of gaseous SN remnants are identifiable in
  our Galaxy
• Well over a thousand (!) pulsars have been
  catalogued in our Galaxy.

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SN 1987A