Transcript 12. Stellar Evolution: The Lives and Deaths of Stars

Astronomy
A BEGINNER’S GUIDE
TO THE UNIVERSE
EIGHTH EDITION
CHAPTER 12
Stellar Evolution
Clickers
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Question 1
Stars like our Sun will end their lives as
a)
b)
c)
d)
e)
red giants.
pulsars.
black holes.
white dwarfs.
red dwarfs.
© 2017 Pearson Education, Inc.
Question 1
Stars like our Sun will end their lives as
a)
b)
c)
d)
e)
red giants.
pulsars.
black holes.
white dwarfs.
red dwarfs.
Explanation: Low-mass stars
eventually swell into red giants,
and their cores later contract
into white dwarfs.
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Question 2
Elements heavier than hydrogen and helium were created
a)
b)
c)
d)
e)
in the Big Bang.
by nucleosynthesis in massive stars.
in the cores of stars like the Sun.
within planetary nebula.
They have always existed.
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Question 2
Elements heavier than hydrogen and helium were created
a)
b)
c)
d)
e)
in the Big Bang.
by nucleosynthesis in massive stars.
in the cores of stars like the Sun.
within planetary nebula.
They have always existed.
Explanation: Massive stars
create enormous core
temperatures as red
supergiants, fusing helium
into carbon, oxygen, and even
heavier elements.
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Question 3
The Sun will evolve away from the main sequence when
a) its core begins fusing iron.
b) its supply of hydrogen is used up.
c) the carbon core detonates, and it explodes as a Type I
supernova.
d) helium builds up in the core, while the hydrogen-burning
shell expands.
e) the core loses all of its neutrinos, so all fusion ceases.
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Question 3
The Sun will evolve away from the main sequence when
a) its core begins fusing iron.
b) its supply of hydrogen is used up.
c) the carbon core detonates, and
it explodes as a Type I supernova.
d) helium builds up in the core,
while the hydrogen-burning
shell expands.
e) the core loses all of its neutrinos, so all fusion ceases.
Explanation: When the Sun’s core becomes unstable and
contracts, additional H fusion generates extra pressure, and the
star will swell into a red giant.
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Question 4
The helium flash occurs
a)
b)
c)
d)
e)
when T-Tauri bipolar jets shoot out.
in the middle of the main-sequence stage.
in the red giant stage.
during the formation of a neutron star.
in the planetary nebula stage.
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Question 4
The helium flash occurs
a)
b)
c)
d)
e)
when T-Tauri bipolar jets shoot out.
in the middle of the main-sequence stage.
in the red giant stage.
during the formation of a neutron star.
in the planetary nebula stage.
Explanation: When the collapsing
core of a red giant reaches high
enough temperatures and
densities, helium can fuse into
carbon quickly—a helium flash.
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Question 5
Stars gradually lose mass as they become white dwarfs
during the
a)
b)
c)
d)
e)
T-Tauri stage.
emission nebula stage.
supernova stage.
nova stage.
planetary nebula stage.
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Question 5
Stars gradually lose mass as they become white dwarfs
during the
a)
b)
c)
d)
e)
T-Tauri stage.
emission nebula stage.
supernova stage.
nova stage.
planetary nebula stage.
Explanation: Low-mass stars forming
white dwarfs slowly lose their outer
atmospheres and illuminate these
gases for a relatively short time.
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Question 6
Astronomers determine the age of star clusters by
observing
a) the number of main-sequence stars.
b) the ratio of giants to supergiants.
c) the luminosity of stars at
the turnoff point.
d) the number of white dwarfs.
e) supernova explosions.
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Question 6
Astronomers determine the age of star clusters by
observing
a) the number of main-sequence stars.
b) the ratio of giants to supergiants.
c) the luminosity of stars at
the turnoff point.
d) the number of white dwarfs.
e) supernova explosions.
Explanation: The H–R diagram
of a cluster can indicate its
Turnoff
approximate age.
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point from
the main
sequence
Question 7
The source of pressure that makes a white dwarf stable is
a)
b)
c)
d)
e)
electron degeneracy.
neutron degeneracy.
thermal pressure from intense core temperatures.
gravitational pressure.
helium–carbon fusion.
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Question 7
The source of pressure that makes a white dwarf stable is
a)
b)
c)
d)
e)
electron degeneracy.
neutron degeneracy.
thermal pressure from intense core temperatures.
gravitational pressure.
helium–carbon fusion.
Explanation: Electrons in the core
cannot be squeezed infinitely close
and prevent a low-mass star from
collapsing further.
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Question 8
In a white dwarf, the mass of the Sun is packed into the
volume of
a)
b)
c)
d)
e)
an asteroid.
a planet the size of Earth.
a planet the size of Jupiter.
an object the size of the Moon.
an object the size of a sugar cube.
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Question 8
In a white dwarf, the mass of the Sun is packed into the
volume of
a)
b)
c)
d)
e)
an asteroid.
a planet the size of Earth.
a planet the size of Jupiter.
an object the size of the Moon.
an object the size of a
sugar cube.
Explanation: The density of a white dwarf is about a million times
greater than normal solid matter.
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Question 9
In a young star cluster, when more massive stars are
evolving into red giants, the least massive stars are
a)
b)
c)
d)
e)
ending their main-sequence stage.
also evolving into red giants.
forming planetary nebulae.
barely starting to fuse hydrogen.
starting the nova stage.
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Question 9
In a young star cluster, when more massive stars are
evolving into red giants, the least massive stars are
a)
b)
c)
d)
ending their main-sequence stage.
also evolving into red giants.
forming planetary nebulae.
barely starting to fuse
hydrogen.
e) starting the nova stage.
Explanation: More massive stars
form much faster and have much
shorter main-sequence lifetimes.
Low-mass stars form more slowly.
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Question 10
A star will spend most of its “shining” lifetime
a)
b)
c)
d)
e)
as a protostar.
as a red giant.
as a main-sequence star.
as a white dwarf.
evolving from type O to type M.
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Question 10
A star will spend most of its “shining” lifetime
a)
b)
c)
d)
e)
as a protostar.
as a red giant.
as a main-sequence star.
as a white dwarf.
evolving from type O to type M.
Explanation: In the mainsequence stage, hydrogen
fuses to helium. Pressure from
light and heat pushing out
balances gravitational pressure
pushing inward.
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Question 11
A nova involves
a) mass transfer onto a white dwarf in a binary star
system.
b) repeated helium fusion flashes in red giants.
c) rapid collapse of a protostar into a massive O star.
d) the explosion of a low-mass star.
e) the birth of a massive star in a new cluster.
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Question 11
A nova involves
a) mass transfer onto a white dwarf in a binary star
system.
b) repeated helium fusion flashes in red giants.
c) rapid collapse of a protostar into a massive O star.
d) the explosion of a low-mass star.
e) the birth of a massive star in a new cluster.
Explanation: Sudden, rapid fusion
of new fuel dumped onto a white
dwarf causes the star to flare up
and for a short time become much
brighter.
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Question 12
What type of atomic nuclei heavier than helium are most
common, and why?
a)
b)
c)
d)
Those heavier than iron, because of supernovae
Iron, formed just before massive stars explode
Odd-numbered nuclei, built with hydrogen fusion
Even-numbered nuclei, built with helium fusion
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Question 12
What type of atomic nuclei heavier than helium are most
common, and why?
a)
b)
c)
d)
Those heavier than iron, because of supernovae
Iron, formed just before massive stars explode
Odd-numbered nuclei, built with hydrogen fusion
Even-numbered nuclei, built
with helium fusion
Explanation: Helium nuclei have
an atomic mass of 4; they act as
building blocks in high-temperature
fusion within supergiants.
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Question 13
A white dwarf can explode when
a)
b)
c)
d)
e)
its mass exceeds the Chandrasekhar limit.
its electron degeneracy increases enormously.
fusion reactions increase in its core.
iron in its core collapses.
the planetary nebula stage ends.
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Question 13
A white dwarf can explode when
a)
b)
c)
d)
e)
its mass exceeds the Chandrasekhar limit.
its electron degeneracy increases enormously.
fusion reactions increase in its core.
iron in its core collapses.
the planetary nebula stage ends.
Explanation: If
additional mass from
a companion star
pushes a white dwarf
beyond 1.4 solar masses,
it can explode in a Type I supernova.
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Question 14
A Type II supernova occurs when
a)
b)
c)
d)
e)
hydrogen fusion shuts off.
uranium decays into lead.
iron in the core starts to fuse.
helium is exhausted in the outer layers.
a white dwarf gains mass.
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Question 14
A Type II supernova occurs when
a)
b)
c)
d)
e)
hydrogen fusion shuts off.
uranium decays into lead.
iron in the core starts to fuse.
helium is exhausted in the outer layers.
a white dwarf gains mass.
Explanation: Fusion of iron
does not produce energy
or provide pressure; the
star’s core collapses
immediately, triggering a supernova explosion.
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Question 15
Supernova 1987A was important because
a)
b)
c)
d)
its parent star had been studied before the explosion.
its distance was already known.
it was observed early, as its light was still increasing.
its evolution was captured with detailed images from
the Hubble Space Telescope.
e) All of the above are true.
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Question 15
Supernova 1987A was important because
a)
b)
c)
d)
its parent star had been studied before the explosion.
its distance was already known.
it was observed early, as its light was still increasing.
its evolution was captured with
detailed images from the
Hubble Space Telescope.
e) All of the above are true.
Explanation: Supernovae are important
distance indicators in the study of
galaxies beyond the Milky Way.
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Question 16
As stars evolve during their main-sequence lifetime,
a) they gradually become cooler and dimmer (spectral type
O to type M).
b) they gradually become hotter and brighter (spectral type
M to type O).
c) they don’t change their spectral type.
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Question 16
As stars evolve during their main-sequence lifetime,
a) they gradually become cooler and dimmer (spectral type
O to type M).
b) they gradually become hotter and brighter (spectral type
M to type O).
c) they don’t change their spectral type.
Explanation: A star’s main-sequence characteristics of surface
temperature and brightness are based on its mass. Stars of
different initial mass become different spectral types on the
main sequence.
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Question 17
More massive white dwarfs are _____ compared with less
massive white dwarfs.
a)
b)
c)
d)
e)
hotter
smaller
larger
cooler
identical in size
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Question 17
More massive white dwarfs are _____ compared with less
massive white dwarfs.
a)
b)
c)
d)
e)
hotter
smaller
larger
cooler
identical in size
Explanation: Chandrasekhar showed that more mass will squeeze
a white dwarf into a smaller volume due to electron degeneracy
pressure.
© 2017 Pearson Education, Inc.