Transcript dtu7ech13 - Fort Thomas Independent Schools

Chapter 13:
The Deaths
of Stars
The Helix Nebula
Planetary Nebulae
NGC 7293,
Helix Nebula
NGC 6826
Menzel 3
From Supergiants to White Dwarfs
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.
Structure of an Old High-Mass Star
Supernovae Proceed Irregularly
Computer simulations showing how chaotic the supernova
is deep inside the star as it begins to explode.
Supernova 1987A
Rotating, Magnetized Neutron Star
Charged particles are accelerated near a neutron star’s
magnetic poles and produce two oppositely directed
beams of radiation.
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?

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

Post–Main-Sequence Evolution of
Low-Mass Stars
Bipolar Planetary Nebula
Sirius and White Dwarf
Sirius B, a white dwarf,
at the five o’clock
position
Both are hot
blackbodies and strong
emitters of X rays
Nova Herculis 1934
Shortly after peak brightness
as a magnitude –3 star.
Two months later, magnitude +12.
Nova Cygni 1975
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.
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.
Cassiopeia A
An X-ray picture of Cassiopeia
A taken by Chandra
Radio image produced by
the Very Large Array (VLA)
Cosmic Ray Shower
Shells of Gas Around SN 1987A
Supernova Light Curves
Recording a Pulsar
PSR 0329+54
Crab Nebula and Pulsar
Observations at different wavelengths give astronomers information
about the nebula’s chemistry, motion, history, and interactions with
preexisting gas and dust.
Crab Nebula and Pulsar
The Crab’s visible flashes and X-ray pulses have identical periods
of 0.033 seconds.
How Magnetic Field Strengths Increase
As a star collapses, it carries the magnetic field
inward, thereby increasing its strength.
Neutron Star’s 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 star’s crust is only 0.3 km thick.
Glitch & the Vela Pulsar’s
Spindown Rate
Double Pulsar
Artist’s conception of PSR J0737-3039
X-Ray Pulses from Centaurus X-3
X ray intensity as detected by Uhuru
Model of a Pulsating X-Ray
Infalling gas is funneled down onto the neutron star’s magnetic
poles, where it strikes the star with enough energy to create two
X-ray–emitting hot spots.
X Rays from an X-Ray Burster
Summary of Stellar Evolution
The evolution of isolated stars depends on their masses.
Summary of Stellar Evolution
WHAT DID YOU THINK?
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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 field’s axis does not
coincide with the rotation axis. The beam of radiation it emits sweeps across our
region of space.
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