Chapter 13: The Deaths of Stars

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Chapter 13The Deaths of Stars
The Helix Nebula
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Planetary Nebulae
NGC 7293, Helix Nebula
NGC 6826
Menzel 3
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From Supergiants to White Dwarfs
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Structure of an Old Low-Mass Star
Near the end of its life, a low-mass star like
the Sun travels up the AGB and becomes a
supergiant.
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Structure of an Old High-Mass Star
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Supernovae Proceed Irregularly
Computer simulations showing how chaotic the
supernova is deep inside the star as it begins to
explode.
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Supernova 1987A
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Rotating, Magnetized Neutron Star
Charged particles are accelerated near a neutron
stars magnetic poles and produce two oppositely
directed beams of radiation.
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WHAT DO YOU THINK?

• Will the Sun someday stop shining? If so, how?
• What is a nova?
• Where do heavy elements on the Earth like carbon,
  silicon, oxygen, iron, and uranium come from?
• What are cosmic rays?
• What is a pulsar?

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You will discover

• what happens to stars when core helium fusion
  ceases
• how heavy elements are created
• the characteristics of the end of stellar
  evolution
• why some stars go out relatively gently, while
  others go with a bang
• the incredible densities of neutron stars and how
  they are observed

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PostMain-Sequence Evolution ofLow-Mass Stars
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Bipolar Planetary Nebula
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Sirius and White Dwarf
Both are hot blackbodies and strong emitters of X
rays
Sirius B, a white dwarf, at the five oclock
position
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Nova Herculis 1934
Shortly after peak brightness as a magnitude 3
star.
Two months later, magnitude 12.
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Nova Cygni 1975
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Supernovae Proceed Irregularly
Chaos helps account for the lopsided distribution
of all elements in this supernova remnant. X-ray
images of a supernova remnant taken by Chandra.
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Gum Nebula
The Gum Nebula, created by a supernova 11,000
years ago, is the largest known supernova
remnant. It now has a diameter of about 2300 ly.
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Cassiopeia A
An X-ray picture of Cassiopeia A taken by Chandra
Radio image produced by the Very Large Array (VLA)
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Cosmic Ray Shower
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Shells of Gas Around SN 1987A
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Supernova Light Curves
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Recording a Pulsar
PSR 032954
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Crab Nebula and Pulsar
Observations at different wavelengths give
astronomers information about the nebulas
chemistry, motion, history, and interactions with
preexisting gas and dust.
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Crab Nebula and Pulsar
The Crabs visible flashes and X-ray pulses have
identical periods of 0.033 seconds.
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How Magnetic Field Strengths Increase
As a star collapses, it carries the magnetic
field inward, thereby increasing its strength.
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Neutron Stars Interior
The neutron star has a superconducting,
superfluid core 9.7 km in radius, surrounded by a
0.6-km-thick mantle of superfluid neutrons. The
neutron stars crust is only 0.3 km thick.
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Glitch the Vela Pulsars Spindown Rate
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Double Pulsar
Artists conception of PSR J0737-3039
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X-Ray Pulses from Centaurus X-3
X ray intensity as detected by Uhuru
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Model of a Pulsating X-Ray
Infalling gas is funneled down onto the neutron
stars magnetic poles, where it strikes the star
with enough energy to create two X-rayemitting
hot spots.
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X Rays from an X-Ray Burster
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Summary of Stellar Evolution
The evolution of isolated stars depends on their
masses.
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Summary of Stellar Evolution
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WHAT DID YOU THINK?

• Will the Sun someday cease to exist? If so, how?
• The Sun will shed matter as a planetary nebula in
  about 6 billion years and then cease nuclear
  fusion. Its remnant white dwarf will dim over the
  succeeding billions of years.
• What is a nova?
• A nova is a relatively gentle explosion of
  hydrogen gas on the surface of a white dwarf in a
  binary star system.
• What are the origins of the carbon, silicon,
  oxygen, iron, uranium, and other heavy elements
  on Earth?
• These elements are created during stellar
  evolution, by supernovae, and by colliding
  neutron stars.
• What are cosmic rays?
• Cosmic rays are high-speed particles (mostly
  hydrogen and other atomic nuclei) in space. Many
  of them are believed to have been created as a
  result of supernovae.
• What is a pulsar?
• A pulsar is a rotating neutron star in which the
  magnetic fields axis does not coincide with the
  rotation axis. The beam of radiation it emits
  sweeps across our region of space.

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Key Terms
asymptotic giant branch (AGB) star Chandrasekhar
limit cosmic ray cosmic ray shower glitch helium
shell flash helium shell fusion lighthouse
model neutron degeneracy pressure neutron star
nova (plural novae) photodisintegration planetary
nebula pulsar quark secondary cosmic
ray supernova Type Ia supernova Type II
supernova white dwarf X-ray burster