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Chapter 12 Stellar Evolution


a) red giants.b) pulsars.c) black holes.d) white dwarfs.e) red dwarfs.

Question 1

Stars like our Sun will end their lives as


a) red giants.b) pulsars.c) black holes.d) white dwarfs.e) red dwarfs.

Question 1

Stars like our Sun will end their lives as

Low-mass stars eventually swell into red giants, and their cores later contract

into white dwarfs.


a) in the Big Bang.b) by nucleosynthesis in massive stars.c) in the cores of stars like the Sun.d) within planetary nebulae.e) They have always existed.

Question 2

Elements heavier than hydrogen and Helium were created


Question 2

Elements heavier than hydrogen and helium were created

Massive stars create enormous core

temperatures as red supergiants, fusing helium into carbon, oxygen, and even heavier elements.

a) in the Big Bang.b) by nucleosynthesis in massive stars. c) in the cores of stars like the Sun.d) within planetary nebula e) They have always existed.


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.

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.

Question 3

The Sun will evolve away from the main sequence when

When the Sun’s core becomes unstable and contracts,

additional H fusion generates extra pressure, and the star will swell into a red giant.


a) when T-Tauri bipolar jets shoot out.b) in the middle of the main sequence stage.c) in the red giant stage.d) during the formation of a neutron star.e) in the planetary nebula stage.

Question 4

The helium flash occurs


a) when T-Tauri bipolar jets shoot out.b) in the middle of the main sequence stage.c) in the red giant stage.d) during the formation of a neutron star.e) in the planetary nebula stage.

Question 4

The helium flash occurs

When the collapsing core of a red giant reaches high

enough temperatures and densities, helium can fuse

into carbon quickly – a helium flash.


a) T-Tauri stage.b) emission nebula stage.c) supernova stage.d) nova stage.e) planetary nebula stage.

Question 5

Stars gradually lose mass as they become white dwarfs during the


a) T-Tauri stage.b) emission nebula stage.c) supernova stage.d) nova stage.e) planetary nebula stage.

Question 5

Stars gradually lose mass as they become white dwarfs during the

Low-mass stars forming white dwarfs slowly lose their outer atmospheres,

and illuminate these gases for a relatively short time.


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.

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.

Question 6

Astronomers determine the age of star clusters by observing

The H–R diagram of a cluster can indicate its approximate age.

Turnoff point from the main sequence


a) electron degeneracy.b) neutron degeneracy.c) thermal pressure from intense core temperatures.d) gravitational pressure.e) helium-carbon fusion.

Question 7

The source of pressure that makes a white dwarf stable is


a) electron degeneracy.b) neutron degeneracy.c) thermal pressure from intense core temperatures.d) gravitational pressure.e) helium-carbon fusion.

Question 7

The source of pressure that makes a white dwarf stable is

Electrons in the core cannot be squeezed infinitely close, and prevent a low-mass star

from collapsing further.


a) an asteroid.b) a planet the size of Earth.c) a planet the size of Jupiter.d) an object the size of the Moon.e) an object the size of a sugar cube.

Question 8

In a white dwarf, the mass of the Sun is packed into the volume of


a) an asteroid.b) a planet the size of Earth.c) a planet the size of Jupiter.d) an object the size of the Moon.e) an object the size of a sugar cube.

Question 8

In a white dwarf, the mass of the Sun is packed into the volume of

The density of a white dwarf is about a million

times greater than normal solid matter.


a) ending their main-sequence stage.b) also evolving into red giants.c) forming planetary nebulae.d) barely starting to fuse hydrogen.e) starting the nova stage.

Question 9

In a young star cluster, when more massive stars are evolving into red giants, the least massive stars are


a) ending their main-sequence stage.b) also evolving into red giants.c) forming planetary nebulae.d) barely starting to fuse hydrogen.e) starting the nova stage.

Question 9

In a young star cluster, when more massive stars are evolving into red giants, the least massive stars are

More massive stars form much faster, and have much shorter

main-sequence lifetimes.

Low-mass stars form more slowly.


a) as a protostar.b) as a red giant.c) as a main-sequence star.d) as a white dwarf.e) evolving from type O to type M.

Question 10

A star will spend most of its “shining” lifetime


a) as a protostar.b) as a red giant.c) as a main-sequence star.d) as a white dwarf.e) evolving from type O to type M.

Question 10

A star will spend most of its “shining” lifetime

In the main-sequence stage, hydrogen fuses to helium.

Pressure from light and heat pushing out balances

gravitational pressure pushing inward.


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.

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.

Question 11

A nova involves

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.


a) those heavier than iron, because of supernovaeb) iron, formed just before massive stars explodec) odd-numbered nuclei, built with hydrogen fusiond) even-numbered nuclei, built with helium fusion

Question 12

What type of atomic nuclei heavier than helium are most common, and why?


a) those heavier than iron, because of supernovaeb) iron, formed just before massive stars explodec) odd-numbered nuclei, built with hydrogen fusiond) even-numbered nuclei, built with helium fusion

Question 12

What type of atomic nuclei heavier than helium are most common, and why?

Helium nuclei have an atomic mass of 4; they act as building

blocks in high-temperature fusion within supergiants.


a) its mass exceeds the Chandrasekhar limit.b) its electron degeneracy increases enormously.c) fusion reactions increase in it’s core.d) iron in its core collapses.e) the planetary nebula stage ends.

Question 13

A white dwarf can explode when


a) its mass exceeds the Chandrasekhar limit.b) its electron degeneracy increases enormously.c) fusion reactions increase in it’s core.d) iron in its core collapses.e) the planetary nebula stage ends.

Question 13

A white dwarf can explode when

If additional mass from a companion star pushes a white dwarf beyond 1.4 solar masses, it can explode in a Type I supernova.


Question 14

A Type II supernova occurs when

a) hydrogen fusion shuts off.b) uranium decays into lead.c) iron in the core starts to fuse.d) helium is exhausted in the outer layers.e) a white dwarf gains mass.


a) hydrogen fusion shuts off.b) uranium decays into lead.c) iron in the core starts to fuse.d) helium is exhausted in the outer layers.e) a white dwarf gains mass.

Question 14

A Type II supernova occurs when

Fusion of iron does not produce energy or provide pressure; the star’s core collapses immediately, triggering a supernova explosion.


a) its parent star had been studied before the explosion.b) its distance was already known.c) it was observed early, as its light was still increasing.d) its evolution was captured with detailed images from the

Hubble Space Telescope.e) All of the above are true.

Question 15

Supernova 1987A was important because


a) its parent star had been studied before the explosion.b) its distance was already known.c) it was observed early, as its light was still increasing.d) its evolution was captured with detailed images from the

Hubble Space Telescope.e) All of the above are true.

Question 15

Supernova 1987A was important because

Supernovae are important distance indicators in the study of galaxies

beyond the Milky Way.


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.

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.

Question 16

As stars evolve during their main-sequence lifetime

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.


a) hotter b) smallerc) largerd) coolere) identical in size

Question 17

More massive white dwarfs are ______ compared with less massive white dwarfs.


a) hotter b) smallerc) largerd) coolere) identical in size

Question 17

More massive white dwarfs are ______ compared with less massive white dwarfs.

Chandrasekhar showed that more mass will squeeze a white dwarf into a smaller volume, due to electron

degeneracy pressure.

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