The Stars
HNRT 227 Chapter 14
22 October 2015
Great Idea:
The Sun and other stars use nuclear fusion
reactions to convert mass into energy. Eventually,
when a star’s nuclear fuel is depleted, the star must
burn out.
1
Chapter Outline
•
•
•
•
The Nature of Stars
The Anatomy of Stars
The Variety of Stars
The Life Cycles of Stars
2
iClicker Question
• How often do you look up at the night
time sky?
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A
B
C
D
Always (when possible)
Often
Sometimes
Never
3
iClicker Question
•
Do you enjoy looking at the stars?
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–
A
B
yes
no
4
The Nature of Stars
5
The Nature of Stars
• Astronomy
– Oldest science (?)
• Star
– Ball of gas
– Fusion reactor
• All stars have a
beginning and an ending
6
Measuring the Stars with
Telescopes and Satellites
• Electromagnetic radiation
• Measurement of photons
–
–
–
–
Wavelength
Intensity
Direction
Variation
7
Telescopes
8
Orbiting Observatories
• Great Observatories Program
– Hubble Space Telescope
– Spitzer Infrared Telescope
– Chandra X-Ray Observatory
9
iClicker Question
•
What source of data is used to analyze
stars?
–
A
–
–
B
C
–
–
D
E
chemical testing of actual samples
of stellar matter
electromagnetic radiation
spacecraft in orbit around distant
stars
both B and C above
no data is used
10
iClicker Question
•
Telescopes are devices that:
–
–
–
–
A
B
C
D
focus and concentrate radiation
magnify only visible light
all use mirrors
both B and C above
11
The Anatomy of Stars
12
The Structure of the Sun
• Structure
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–
–
–
–
–
Stellar core
Radiative zone
Convection zone
Photosphere
Chromosphere
Corona
• Solar Wind
– Stream of
particles
13
Our Sun
14
More On Solar Structure
• Hydrogen fusion takes place
in a core extending from
the Sun’s center to about
0.25 solar radius
• The core is surrounded by a
radiative zone extending to
about 0.71 solar radius
– In this zone, energy travels
outward through radiative
diffusion
• The radiative zone is
surrounded by a rather
opaque convective zone of
gas at relatively low
temperature and pressure
– In this zone, energy travels
outward primarily through
convection
15
How do we know the Sun’s interior?
• Helioseismology is
the study of how the
Sun vibrates
• These vibrations have
been used to infer
pressures, densities,
chemical
compositions, and
rotation rates within
the Sun
16
Magnetic Fields
17
Northern Lights (Aurora Borealis)
18
The Sun’s Energy
Source: Fusion
•
•
•
Sun’s Energy Source
–
–
Historical
Current
•
hydrogen
Fusion
–
3-steps-hydrogen burning
1) P + P  D + e+ + neutrino + energy
2) D + P  3He + photon + energy
3) 3He + 3He 4He + 2protons + photon + energy
Life expectancy
–
11-12 billion years
19
The Variety of Stars
• Differences
– Color
– Brightness
• Distance
• Absolute
brightness
– Energy output
– luminosity
• Apparent
brightness
• Behavior
– Total mass
– age
20
The Cosmic
Distance Ladder
• Distance
– Light-years
• Measurement
– Triangulation
(parallax)
– Spectroscopic
parallax
– Cepheid variable
– Tully-Fisher
– Supernovae Type Ia
– Hubble’s Law
21
The Hertzsprung-Russel
Diagram
• Star Groupings
– Main-sequence stars
– Red giants
– White dwarfs
22
Step 1 to an H-R Diagram
20
15
10
Absolute Magnitude
• Plot for
the 20
nearest
and
brightest
stars to
Earth
Not an H-R Diagram
5
0
0
5000
10000
15000
20000
25000
30000
-5
-10
Temperature
23
Step 2 to an H-R Diagram
• Reversing
the y-axis
Getting Closer to an H-R Diagram
Temperature (K)
-10
-5
Absolute Magnitude
0
5
10
15
20
0
5000
10000
15000
20000
25000
2430000
Step 3 to an H-R Diagram
• Reversing the
x-axis
– Lowest
temperature
to the right
Now it's looking Like an H-R Diagram
Temperature (K)
-10
-5
5
10
15
20
30000
25000
20000
15000
10000
5000
0
25
Absolute Magnitude
0
A Standard H-R Diagram
26
iClicker Question
•
Compared with other stars, our Sun is:
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–
–
A
B
C
an unusually large star
not a star at all
a rather ordinary star
27
iClicker Question
•
The outer part of the Sun, the part
that actually emits most of the light
we see, is called the:
–
–
–
–
–
A
B
C
D
E
chromosphere
convective zone
photosphere
core
radiative zone
28
iClicker Question
•
The solar wind is composed of:
–
–
–
–
A
B
C
D
and
bits of neutral gas
all kinds of organic substances
air
charged particles including hydrogen
helium ions
29
iClicker Question
•
Northern lights result from
interactions of:
–
A
–
B
–
C
the Sun’s magnetic field with
Earth’s gravity
UV light from the Sun with Earth’s
ozone layer
the solar wind with the Earth’s
magnetic field
30
iClicker Question
•
The Sun’s peak output of energy is in:
–
A
–
B
–
C
the ultraviolet portion of the
electromagnetic spectrum
the visible portion of the
electromagnetic spectrum
the infrared portion of the
electromagnetic spectrum
31
iClicker Question
•
What is the Sun’s energy source?
–
A
–
–
–
–
B
C
D
E
combustion of hydrogen rich
chemical fuels
fusion of hydrogen
fission of hydrogen
radioactive decay
gravitational collapse
32
The Life Cycles of Stars
33
The Birth of Stars
• Nebular Hypothesis
– Laplace
34
The Main Sequence and
the Death of Stars
• Stars much less massive
than the Sun
– Glows 100 billion years
• No change in size,
temperature, energy
output
– Brown dwarfs
• Some don’t consider these
stars
35
The Main Sequence and
the Death of Stars
• Stars about the
mass of the sun
– Hydrogen burning at
faster rate
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–
–
–
• Move off main
sequence
Helium burning
Red giant
Begin collapse
White dwarf
36
The Life Cycle of a Star Like the
Sun
•
•
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•
•
•
•
•
Gas cloud
Fragmentation
Protostar
Kelvin-Helmholz
contraction
Hayashi Track
Ignition
Adjustment to Main
Sequence
Hydrogen Core
Depletion
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•
•
•
•
•
•
•
Hydrogen shell burning
Helium flash
Helium core burning
Helium core depletion
Helium shell burning
Helium shell flashes
Planetary nebula
White Dwarf
37
Sun’s Life Cycle on H-R Diagram
H-R Diagram with annotations for Stellar Stages
Temperature (log)
100000
10000
1000
-10
Planetary Nebula
Asymptotic
Branch
Horizontal
Branch
Helium
Flash
-5
Kelvin-Helmholtz
Contraction
Adjust to
Main
Sequence
5
Absolute Magnitude
0
Sub
Giant Hayashi
Core
Track
Contraction
10
White
Dwarf
15
38
20
The Main Sequence and
the Death of Stars
• Very Large Stars
– Successive collapses
and burnings
– Iron core
– Catastrophic
collapse
• supernova
39
Layers of Massive Star
H -> He
Layers
of
He -> C
C -> O
O ->
Ne
Ne
-> Mg
Nuclear
Fusion
Mg ->
in
High
Mass
Stars
Si
Si -> Fe
Fe
40
Neutron Stars and Pulsars
• Neutron Star
– Dense and small
– High rotation rate
– Little light
• Pulsar
– Special neutron star
– Electromagnetic radiation
– End state of supernova
41
Black Holes
• Black Hole
– Result of collapsed
large star
– Nothing escapes
from surface
– Cannot “see” them
• See impact on
other stars, dust,
etc.
• Detect x-rays,
gamma rays
42
iClicker Question
•
It is estimated that the total lifetime
of our Sun is 12 billion years. Roughly,
how far is it through its hydrogenburning phase now?
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–
–
–
A
B
C
D
10%
25%
50%
90%
43
iClicker Question
•
Triangulation and Cepheid variables
are methods to measure:
–
–
–
–
A
B
C
D
distances to stars
energy output of stars
lifetime of stars
composition of stars
44
iClicker Question
•
A Hertzsprung-Russell diagram plots a
star’s temperature versus its:
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–
–
–
–
A
B
C
D
E
color
distance
age
size
energy output
45
iClicker Question
•
Large dust and gas clouds are
commonly found throughout space.
They are called:
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–
–
–
–
A
B
C
D
E
red giants
galaxies
nebulae
supernovae
white dwarfs
46
iClicker Question
•
The fusion process in very large stars
produces chemical elements up to:
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–
A
B
C
D
E
He
C
Fe
U
Pb
47
iClicker Question
•
All natural elements beyond iron are
created in:
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–
–
A
B
C
supernova explosions
fusion of very large stars
the big bang
48
iClicker Question
•
An object that is so dense and massive
that nothing, including light can escape
from its surface is called:
–
–
–
–
–
A
B
C
D
E
a
a
a
a
a
supernova
red giant
white dwarf
black hole
neutron star
49
iClicker Question
•
Are you surprised that the chemical
elements about you were made in a
supernova?
–
–
A
B
Yes
No
50