TEST BANK 21ST CENTURY ASTRONOMY THE SOLAR SYSTEM 5TH EDITION BY KAY
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Chapter 16: Evolution of
Low-Mass Stars
Learning
Objectives
Define the bold-faced vocabulary terms within the chapter.
16.1 The Life of a Main-Sequence Star
Depends on Its Mass
Distinguish between low-, intermediate-, and high-mass stars.
Multiple Choice: 2, 4, 15
Short Answer: 2
Illustrate why mass and luminosity dictate the lifetime of a
main-sequence star.
Multiple Choice: 1, 5, 10, 12, 14, 18, 19
Short Answer: 1, 3
Describe the change in a star’s structure over its
main-sequence lifetime.
Multiple Choice: 3, 6, 7, 13, 16, 17
Short Answer: 5
16.2 The Star Leaves the Main Sequence
Compare and contrast the behavior of normal and degenerate
gases.
Multiple Choice: 22, 31
Short Answer: 7, 12
Illustrate how shell burning around an inert core drives a
star up and to the right (e.g., the red-giant branch) of the H-R diagram.
Multiple Choice: 26, 30, 33, 34, 35, 36, 37
Short Answer: 8, 9
Describe the change in a star’s structure from when it begins
shell burning until it climbs the red-giant branch.
Multiple Choice: 20, 21, 23, 24, 25, 27, 28, 29, 32, 38
Short Answer: 10, 11
16.3 Helium Burns in the Degenerate Core
Explain how helium is burned via
the triple-alpha process.
Multiple Choice: 39, 41
Short Answer: 13, 15
Illustrate why the ignition of fusion in degenerate material
leads to an explosion.
Multiple Choice: 40
Short Answer: 14
Describe the change in a star’s structure from when it begins
triple-alpha burning until it settles on the horizontal branch.
Multiple Choice: 42, 43
Short Answer: 16, 17, 18
16.4 Dying Stars Shed Their Outer Layers
Compare and contrast the internal structure of red-giant and
asymptotic-giant branch stars.
Multiple Choice: 45
Illustrate how mass-loss from an AGB star creates a planetary
nebula and white dwarf.
Multiple Choice: 46, 49, 55, 56, 57
Short Answer: 19, 22
Explain the sources of radiation from planetary nebulae and
white dwarfs.
Multiple Choice: 51
Short Answer: 21
Describe how stellar evolution and mass loss effect planets
around a low-mass star.
Multiple Choice: 58
Short Answer: 23
Describe the change in a star’s structure from when it climbs
the AGB until it becomes a cooling white dwarf.
Multiple Choice: 48, 50, 52, 53, 54, 59, 60
Short Answer: 20, 24
16.5 Binary Star Evolution
Explain how a binary system of stars is able to transfer mass
between each star.
Multiple Choice: 68
Short Answer: 25
Illustrate the sequence of evolutionary stages in a close
binary system with mass transfer.
Multiple Choice: 8, 62, 66
Short Answer: 28
Differentiate the causes and characteristics of novae and
Type Ia supernovae.
Multiple Choice: 61, 63, 64, 65, 67, 69, 70
Short Answer: 26, 27, 29, 30
Working It Out 16.1
Estimate the main-sequence lifetime of a star using its mass.
Multiple Choice: 9, 11
Short Answer: 4, 6
Working It Out 16.2
Determine the escape speed from the surface of a star.
Multiple Choice: 44, 47
MULTIPLE CHOICE
1.
What factor is most
important in determining a star’s position on the main sequence and subsequent
evolution?
a.
temperature
b.
pressure
c.
mass
d.
radius
e.
color
2.
The evolutionary cutoff
between low- and high-mass stars occurs at approximately
a.
1.5 M⊙.
b.
1 M⊙.
c.
3 M⊙.
d.
5 M⊙.
e.
10 M⊙.
3.
A 10 M⊙ star will evolve through the same phases as a
a.
1 M⊙ star.
b.
5 M⊙ star.
c.
20 M⊙ star.
d.
0.5 M⊙ star.
4.
If a main-sequence
star’s core temperature increased, fusion reaction rates would ________ because
the protons would be moving _______.
a.
decrease; slower
b.
increase; faster
c.
increase; slower
d.
remain unchanged; the
same speed as before
5.
The __________ a
main-sequence star is, the more hydrogen it has to burn, and the ______ its
main-sequence lifetime lasts.
a.
more massive; shorter
b.
more massive; longer
c.
less massive; shorter
d.
larger; longer
6.
Stars evolve primarily
because
a.
they convert all their
mass to energy.
b.
they lose all their
mass into space.
c.
their core temperatures
decrease steadily as they evolve.
d.
they use up the fuel in
their cores.
7.
The percentage of
hydrogen in the Sun’s core today is roughly_______ of what it was originally.
a.
half
b.
one third
c.
one quarter
d.
less than ten percent
.
8.
If a main-sequence star
were gaining mass by being in an interacting binary system, what would happen
to that star’s luminosity and why?
a.
The luminosity would
increase because the star would become a nova.
b.
The luminosity would
increase because the star’s central pressure would rise and the rate of nuclear
reactions would increase.
c.
The luminosity would
decrease because the outgoing energy has to pass through more layers in the
star.
d.
The luminosity would
decrease because high-mass stars are fainter.
e.
The luminosity would
decrease because the star would quickly turn into a white dwarf.
9.
The main-sequence
lifetime of a star is given by which equation?
a.
t ∝ M/L
b.
t ∝ L/M
c.
t ∝ M 2/L
d.
t ∝ L2/L
e.
t ∝ M/L2
10.
Which star spends the
longest time as a main-sequence star?
a.
0.5 M⊙
b.
1 M⊙
c.
3 M⊙
d.
6 M⊙
e.
10 M⊙
11.
How long will a 2 M⊙ star live as a
main-sequence star?
a.
12 million years
b.
180 million years
c.
1.8 billion years
d.
12 billion years
e.
18 billion years
12.
If the Milky Way formed
stars at approximately a constant rate over the last 14 billion years, what
fraction of the M-type stars that ever formed in it can still be found as
main-sequence stars today? (Note that M-type stars have a mass of approximately
0.5 M⊙.)
a.
10 percent
b.
33 percent
c.
50 percent
d.
75 percent
e.
100 percent
13.
For main-sequence stars
in hydrostatic equilibrium, at any interior radius there exists a balance
between the downward gravitational force at that radius and the
a.
pressure from a
degenerate electron core.
b.
convective force of
material rising from the interior.
c.
energy released from
fusion reactions in the core.
d.
outward gas pressure
from the material inside that radius.
e.
energy released by
fusion reactions in a shell surrounding the degenerate core.
14.
Use the figure shown
below and the relationship t ∝ M/L to estimate the
main-sequence lifetime of a star with a mass equal to 10 times that of the Sun.
(Note that the Sun’s main-sequence lifetime is about 1010 years.)
a.
3 million years
b.
30 million years
c.
300 million years
d.
3 billion years
e.
30 billion years
15.
Using the data in the
figure shown below, identify the spectral type of a star that has a
main-sequence lifetime of about 10 billion years.
a.
A5
b.
F5
c.
K0
d.
G2
e.
M8
16.
As a main-sequence star
burns its core supply of hydrogen, what happens?
a.
Helium begins to fuse
throughout the core.
b.
Helium fuses in a shell
surrounding the core.
c.
Helium fusion takes
place only at the very center of the core, where temperature and pressure are
highest.
d.
helium builds up in the
core.
e.
Helium builds up
everywhere in the star’s interior.
17.
A main-sequence star is
unique because
a.
hydrostatic equilibrium
exists at all radii.
b.
energy transport occurs
via convection throughout much of its interior.
c.
carbon burning occurs
in its core.
d.
it emits strong surface
winds.
e.
hydrogen burning occurs
in its core.
18.
Considering how long it
took for life to arise on Earth, which of the stellar spectral types shown
below would be the least likely to have planets with life?
a.
B0
b.
G2
c.
K0
d.
M0
e.
M5
19.
The luminosity of a
star depends on
a.
its mass and age.
b.
its mass.
c.
its age.
d.
its distance.
e.
its mass, age, and
distance.
20.
When a star depletes
its core supply of hydrogen, _________ causes the core to collapse while
increased gas _________ is exerted on the atmosphere.
a.
pressure; pressure
b.
radiation; gravity
c.
gravity; gravity
d.
gravity; pressure
e.
gravity, radiation
21.
The Sun will become a
red giant star in about
a.
15 billion years.
b.
10 billion years.
c.
5 billion years.
d.
1 billion years.
22.
___________ keeps the
core of a red giant star from collapsing.
a.
Pressure from protons
b.
Pressure from neutrons
c.
Radiation pressure from
hydrogen fusion
d.
Degenerate pressure
from electrons
23.
Place the evolutionary
stages shown in the figure below in order from youngest to oldest.
a.
1, 2, 3
b.
2, 3, 1
c.
3, 2, 1
d.
3, 1, 2
e.
2, 1, 3
24.
Once the core of a
low-mass main-sequence star runs out of hydrogen, ____________ stops until the
core temperature is high enough for helium fusion to begin.
a.
hydrogen fusion
throughout the star
b.
hydrogen fusion in the
core
c.
hydrogen fusion near
the surface
d.
helium fusion
throughout the star
25.
When a star burns
hydrogen in a shell, how does the energy released compare with when the star
burned hydrogen in the core?
a.
There will be an equal
amount of energy produced.
b.
There will be less
energy produced.
c.
There will be more
energy produced.
d.
There will be more
energy produced only if the star’s mass exceeds that of the Sun.
26.
A low-mass star that
burns helium in its core and hydrogen in a shell surrounding the core is
________ than a similar star that burns hydrogen only _________.
a.
more luminous; in its
core
b.
more luminous; in a
shell around a degenerate core
c.
less luminous; in a
shell around a degenerate core
d.
less luminous; in its
core
27.
If there were mixing
processes in a main-sequence star with a radiative zone (there aren’t) that
churned up all the material in the interior, we would expect that the
main-sequence lifetime would be _________ because _________.
a.
shorter; because the
star would turn into a giant faster
b.
shorter; because the
star would burn hydrogen faster and have a higher luminosity
c.
longer; because helium
nuclei have a higher mass than hydrogen nuclei
d.
shorter; because the
star would never turn into a red giant
e.
longer; because more
hydrogen would be available to burn
28.
The Sun will likely
stop being a main-sequence star in
a.
5,000 years.
b.
5 million years.
c.
50 million years.
d.
500 million years.
e.
5 billion years.
29.
During evolutionary
phase A in the figure shown below, the star is _________. In evolutionary phase
B, it is _________.
a.
expanding; expanding
b.
expanding; contracting
c.
contracting; losing
mass
d.
contracting;
contracting
e.
gaining mass; contracting
30.
Using the figure shown
below, identify the star with the smallest radius.
a.
star A
b.
star B
c.
star C
d.
star D
e.
star E
31.
Degenerate refers to a state of matter at
a.
low density.
b.
high density.
c.
low luminosity.
d.
high luminosity.
e.
high temperature.
32.
A 1-M⊙ red giant star’s
energy comes from
a.
hydrogen burning to
helium in its core.
b.
helium burning to
carbon in its core.
c.
hydrogen burning to
helium in a shell surrounding its core.
d.
helium burning to
carbon in a shell surrounding its core.
e.
hydrogen burning to
carbon in a shell surrounding its core.
33.
As a red giant star
evolves, hydrogen shell burning proceeds increasingly faster due to
a.
rotational energy from
the star’s rapid rotation.
b.
heat released from the
core’s contraction.
c.
pressure from the
contracting envelope.
d.
release of energy
stored in magnetic fields.
e.
energy from the fusion
of heavier elements.
34.
When a spectral-type G2
star like the Sun leaves the main sequence, its
a.
luminosity and surface
temperature both stay the same.
b.
luminosity and surface
temperature both decrease.
c.
luminosity increases
and its surface temperature decreases.
d.
luminosity and surface
temperature both increase.
e.
luminosity decreases
and its surface temperature increases.
35.
What is the radius of a
red giant star that has a luminosity of 300 L⊙ and a temperature of
4000 K? (Note that the temperature of the Sun is 5800 K.)
a.
8 R⊙
b.
13 R⊙
c.
25 R⊙
d.
36 R⊙
e.
65 R⊙
36.
As a subgiant star
becomes a red giant, its luminosity increases while its temperature remains
approximately constant. What does this mean?
a.
The radius is
decreasing.
b.
The radius is
increasing.
c.
The star is getting
hotter.
d.
The star is losing
mass.
e.
The star is rotating
more slowly.
37.
As a low-mass
main-sequence star runs out of fuel in its core, it grows more luminous. How is
this possible?
a.
It explodes.
b.
It begins to fuse
helium in the core.
c.
The core expands as it
runs out of fuel.
d.
The core shrinks,
bringing more hydrogen fuel into the burning region.
e.
Convection takes place
throughout the interior, bringing more fuel to the core.
38.
A low-mass
main-sequence star’s climb up the red giant branch is halted by
a.
the end of hydrogen
shell burning.
b.
the beginning of helium
fusion in the core.
c.
electron-degeneracy
pressure in the core.
d.
instabilities in the
star’s expanding outer layers.
e.
an explosion that
destroys the star.
39.
Helium burns in the
core of a horizontal branch star via _________ and produces _________.
a.
the triple-alpha
reaction; carbon
b.
the proton-proton
chain; lithium
c.
the triple-alpha
reaction; oxygen
d.
the proton-proton
chain; iron
e.
the proton-proton
chain; calcium
40.
When helium fusion
begins in the core of a red giant star, the situation quickly gets out of
control because electron-degeneracy pressure does not respond to changes in
a.
luminosity.
b.
density.
c.
gravity.
d.
temperature.
e.
magnetic field
strength.
.
41.
What is the name of the
nuclear reaction illustrated in the figure shown below?
a.
the proton-proton chain
b.
the CNO cycle
c.
beta decay
d.
the triple-alpha
process
e.
the alpha-beta reaction
42.
During which phase of
the evolution of a low-mass star does it have two separate regions of nuclear
burning occurring in its interior?
a.
pre–main sequence
b.
main sequence
c.
red giant
d.
horizontal branch
e.
white dwarf
43.
A star’s surface
temperature during the horizontal branch phase is determined primarily by its
a.
luminosity.
b.
mass and chemical
composition.
c.
magnetic field
strength.
d.
rotation rate.
e.
radius.
44.
A particular asymptotic
giant branch star has approximately the same mass as the Sun but 100 times its
radius. Compared with the Sun, what is the escape velocity from that star?
a.
0.01 times that of the
Sun
b.
0.1 times that of the
Sun
c.
the same as that of the
Sun
d.
10 times that of the
Sun
e.
100 times that of the
Sun
45.
Asymptotic giant-branch
stars have _________ luminosities, _________ radii, and _________ escape
velocities.
a.
large; large; large
b.
large; small; large
c.
large; large; small
d.
small; large; small
e.
small; small; large
46.
Asymptotic giant branch
stars have high-mass loss rates because they
a.
are rotating quickly.
b.
have weak magnetic
fields.
c.
have strong magnetic
fields.
d.
have low surface
gravity.
e.
have high surface
temperatures.
47.
What is the escape
velocity from the surface of a 1 M⊙ AGB star that has a radius of 100 R⊙?
a.
60 km/s
b.
120 km/s
c.
240 km/s
d.
620 km/s
e.
800 km/s
48.
When a low-mass star
becomes an AGB star and has a temperature of 3300 K, at what wavelength will it
shine the brightest?
a.
650 nm, red visible
b.
880 nm, infrared
c.
2.5 µm, infrared
d.
1 mm, microwave
e.
10 m, radio
49.
A star like the Sun
will lose about _________ of its mass before it evolves to become a white
dwarf.
a.
3 percent
b.
30 percent
c.
60 percent
d.
75 percent
50.
What is a planetary
nebula?
a.
a planet surrounded by
a glowing shell of gas
b.
the disk of gas and
dust surrounding a young star that will soon form a star system
c.
the ejected envelope of
a giant star surrounding the remnant of a star
d.
a type of young,
medium-mass star
e.
leftover gas from a supernova
explosion
51.
What ionizes the gas in
a planetary nebula and makes it visible?
a.
X-ray photons emitted
by a pulsar
b.
ultraviolet photons
emitted by a white dwarf
c.
the shock wave from a
supernova
d.
hydrogen burning in the
nebular gas
e.
infrared photons from a
nova explosion
52.
Stars with masses
similar to the Sun will lose _________ of their mass before they become white
dwarfs.
a.
about 10 percent
b.
about 30 percent
c.
nearly all
d.
none
53.
The Sun eventually will
become a(n)
a.
nova.
b.
neutron star.
c.
black hole.
d.
white dwarf.
54.
A star like the Sun
will eventually become a(n) __________ star.
a.
proton degenerate brown
dwarf
b.
neutron degenerate
black hole
c.
electron degenerate
white dwarf
d.
electron degenerate red
dwarf
55.
What would you need to
measure in a planetary nebula to determine how long ago its parent star died?
a.
the mass of the white
dwarf
b.
the mass and radius of
the white dwarf
c.
the nebula’s
temperature and radius
d.
the nebula’s radius and
expansion velocity
e.
the composition of the
gas in the nebula
56.
The Ring Nebula is a
planetary nebula that currently has a radius of 1.2 × 1013
km and an expansion velocity of 250 km/s. Approximately how long ago did its
parent star die and eject its outer layers?
a.
1,500 years ago
b.
3,200 years ago
c.
5,400 years ago
d.
8,000 years ago
e.
28,000 years ago
57.
The gas in a planetary
nebula is composed of
a.
primarily hydrogen from
the surrounding interstellar medium.
b.
primarily hydrogen from
the post-asymptotic giant branch star.
c.
hydrogen and heavier
elements like helium and carbon processed in the core of the post-asymptotic
giant branch star.
d.
primarily helium from
the post-asymptotic giant branch star.
e.
carbon and helium from
the nuclear reactions that took place on the horizontal branch.
58.
A white dwarf with a
temperature of 30,000 K would shine brightest at what wavelength?
a.
4 nm, X-rays
b.
100 nm, ultraviolet
c.
400 nm, blue visible
d.
1 µm, infrared
e.
10 µm, infrared
59.
As a white dwarf star
gradually cools, its radius stays approximately constant. What is happening to
the white dwarf’s luminosity?
a.
It stays the same.
b.
It increases.
c.
It increases then
decreases periodically.
d.
It decreases.
e.
You can’t tell from the
information given.
60.
In a white dwarf, what
is the source of pressure that halts its contraction as it cools?
a.
thermal pressure of the
extremely hot gas
b.
electrons packed so
closely that they become incompressible
c.
neutrons that resist
being pressed further together
d.
carbon nuclei that
repel each other strongly because they each contain six protons
e.
rapid rotation
61.
What are two ways that
Type Ia supernovae can be produced?
a.
mass transfer and
stellar mergers
b.
helium flash and
stellar mergers
c.
mass transfer and
helium flash
d.
helium burning and mass
transfer
e.
carbon burning and mass
transfer
62.
One star in a binary
will almost always become a red giant before the other because
a.
one star is always
larger in radius than the other.
b.
binaries always have
one star twice as massive as the other.
c.
small differences in
main-sequence masses yield large differences in main-sequence ages.
d.
the more massive binary
star always gets more mass from the less massive binary star when both are
main-sequence stars.
e.
one star always spins
faster than the other.
63.
A nova is the result of
which explosive situation?
a.
mass transfer onto a
white dwarf
b.
helium burning in a
degenerate stellar core
c.
a white dwarf that
exceeds the Chandrasekhar limit
d.
the collision of
members of a binary system
e.
runaway nuclear
reactions in the core
64.
A 1-M⊙ star in a binary
system could create which chemical element and eject it into the interstellar
medium?
a.
carbon
b.
helium
c.
iron
d.
all of the above
65.
A Type Ia supernova
occurs when a white dwarf exceeds a mass of
a.
0.8 M⊙.
b.
1.4 M⊙.
c.
2.3 M⊙.
d.
5.4 M⊙.
e.
10 M⊙.
66.
Novae and Type Ia
supernovae can occur in binary star systems because __________ can mean large
differences in their __________.
a.
large differences in
the stars’ temperatures; sizes
b.
small differences in
the stars’ masses; main-sequence lifetimes
c.
small differences in the
stars’ sizes; main-sequence lifetimes
d.
small differences in
the stars’ separation; main-sequence lifetimes
67.
A Type Ia supernova can
be as luminous as
a.
10 billion suns.
b.
1 billion suns.
c.
1 million suns.
d.
1,000 suns.
68.
You observe a 0.8 M⊙ white dwarf in a binary orbit around a main-sequence star of
mass 1.4 M⊙. Which of the following is most likely the original mass of
the star that became the white dwarf?
a.
0.5 M⊙
b.
1 M⊙
c.
0.8 M⊙
d.
1.4 M⊙
e.
3 M⊙
69.
If an 0.8 M⊙ white dwarf could accrete matter from a binary companion at a
rate of 10−9 M⊙/yr, how long would it
take before it exploded as a Type Ia supernova?
a.
600 thousand years
b.
20 million years
c.
200 million years
d.
600 million years
e.
1 billion years
70.
A Type Ia supernova has
a luminosity of approximately
a.
10 thousand L⊙.
b.
10 million L⊙.
c.
1 billion L⊙.
d.
10 billion L⊙.
e.
10 trillion L⊙.
SHORT ANSWER
1.
In what two ways does
temperature affect the rate of nuclear reactions?
2.
How many times more
luminous is a 5 M⊙ star compared with a 2 M⊙ star?
3.
Why does the core of a
main-sequence star have to be hotter to burn helium into carbon than hydrogen
into helium?
4.
Calculate the
main-sequence lifetimes of the following stars of different spectral types: B0
(18 M⊙), B5 (6 M⊙), A5 (2 M⊙), F5 (1.3 M⊙), and M0 (0.5 M⊙). What trend do you notice in your results?
5.
Consider the figure
shown below, where the evolution in chemical composition of the Sun’s interior
is shown at three different times during its life. How do the relative
percentages of hydrogen and helium change at a fractional radius of 0.1 solar
radii, from the time the Sun formed until it exhausts its core supply of
hydrogen in 5 billion years?
6.
How many times longer
does a 2 M⊙ main-sequence star live compared to a 10 M⊙ main-sequence star?
7.
Consider a red giant
star with a luminosity of 200 L⊙ and a radius of 50 R⊙. Using the luminosity–temperature-
radius relationship (L ∝ R2T 4), calculate how hot this star’s surface temperature will be
compared to the Sun, whose temperature is 5,800 K.
8.
Consider a 1 M⊙ star’s journey up the
red giant branch. Its luminosity will change from 10 L⊙ to nearly 1,000 L⊙. How will its
temperature and radius change as the star ascends? (Recall that L ∝ R2T4.)
9.
What stops a red giant
from cooling to continuously lower temperatures, and why?
10.
Describe the structure
of a red giant star just before the helium flash takes place. How does this
compare with the structure of a horizontal-branch star?
11.
How can the core of a
star be degenerate with respect to the electrons but nondegenerate with respect
to the nuclei?
12.
Explain what the
triple-alpha process is and when it takes place in evolving stars.
13.
Describe the helium
flash that occurs when helium fusion ignites in the core of a red giant star.
14.
The 8Be
nucleus is highly unstable, and would break apart after only 10-12
seconds if left alone. Explain why it is nevertheless able to participate in
the triple alpha process.
15.
What causes a star to
leave the red giant phase and settle on the horizontal branch?
16.
Why is a star’s time as
a horizontal branch star so much shorter than its time as a main sequence star?
17.
When the Sun becomes an
AGB star, its radius will be approximately 100 R⊙. If its mass at this
point will be approximately the same as it is now, how will its surface gravity
as an AGB star compare to its present surface gravity as a main-sequence star?
(Note that g = GM/R2.)
18.
What is the shortest
phase of evolution for a one solar mass star that we can visibly see?
19.
What is “degenerate” in
the degenerate core of a white dwarf?
20.
A white dwarf star has
a luminosity equal to 10−4 L⊙ and a temperature
twice that of the Sun (i.e., T = 10,600 K). What
is the radius of the white dwarf, expressed as a ratio to the solar radius?
21.
Explain why stars are
able to lose mass as they expand to red giant size.
22.
Explain which types of
main-sequence stars would be more likely to have planets with complex life.
23.
What is a planetary
nebula, and why are many planetary nebulae not symmetrical?
24.
Explain the
significance of Roche lobes in a binary system.
25.
What types of chemical
elements can low-mass stars contribute to the enrichment of the interstellar
medium and how are they produced?
26.
Why are novae thought
to reoccur repeatedly?
27.
What types of stars
cause Type Ia supernovae, and what makes them explode?
28.
How can a Type Ia be
distinguished, and how can its distance be measured from observations?
29.
Describe the
similarities and differences between the helium flash in the core of a red
giant star and the explosive hydrogen burning on the surface of a white dwarf
star.
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