Deck 13: Stellar Evolution: the Lives and Deaths of Stars

Question 1

Our Sun will fade in luminosity as its supply of hydrogen drops in a billion years.

Answer 1

False

Question 2

A typical star burns helium for about the same amount of time it burns hydrogen.

Answer 2

False

Question 3

Paradoxically, while the core of the red giant is contracting and heating up, its radiation pressure causes its photosphere to swell up and cool off.

Answer 3

True

Question 4

Once the helium flash occurs at stage 10, the star stabilizes again on the horizontal branch of the H- R diagram, but now hundreds of times as bright as on the main sequence.

Question 5

The initial rise off the main sequence in stage 8 comes from gravitational energy of the contracting helium core.

Question 6

All stars have roughly the same luminosity after the helium flash.

Question 7

About 90% of the star's total life is spent on the main sequence.

Question 8

The luminosity of the red giant during its second trip to the upper right on the H- R diagram is less than before the helium flash expansion.

Question 9

The main reason that stars evolved off the main sequence is because they are becoming less massive as energy is lost into space from the proton- proton cycle.

Question 10

Helium fusion requires a higher temperature than hydrogen fusion.

Question 11

The helium flash increases the star's luminosity.

Question 12

The least massive red main- sequence stars may have lifetimes of a trillion years.

Question 13

The helium flash stage lasts several thousand years.

Question 14

Low- mass stars may become hundreds of times more luminous as giants than they were on the main sequence.

Question 15

A star system may undergo two or more nova outbursts.

Question 16

As a main- sequence star, the Sun's hydrogen supply should last about 10 billion years from the zero- age main sequence until its evolution to the giant stages.

Question 17

The helium flash shows up on the H- R diagram on the way to the horizontal branch.

Question 18

While more massive than most of its neighbors, our Sun is still technically a low- mass star.

Question 19

Our Sun should become a planetary nebula in another five billion years.

Question 20

A star may undergo two or more red giant expansion stages.

Question 21

It is the formation of iron in an evolved giant's core that triggers a Type II supernova event.

Question 22

White dwarfs were once the cores of stars that produced planetary nebulae.

Question 23

The density of white dwarf stars is about a million times that of the Sun.

Question 24

Our Sun will eventually become a nova.

Question 25

Compared to the interstellar medium, the gases in a planetary nebula will be richer in helium and carbon.

Question 26

Solar mass stars eventually become hot enough for carbon nuclei to fuse together.

Question 27

A massive star may change its color and size notably, but its high luminosity remains fairly constant.

Question 28

Although mass transfer can occur in binary stars, the small mass change does not impact the evolution of either companion.

Question 29

Only low mass stars experience the temporary instability of the helium flash; high mass stars go directly into heavier element formation.

Question 30

Our Sun will first become a red giant, then a white dwarf, and finally a brown dwarf.

Question 31

Today the majority of the mass of the universe is already in the form of black dwarfs, the solution to the "dark matter" problem.

Question 32

In the cores of the most massive stars, the electrons and protons fuse together and form neutrons.

Question 33

Our Sun will never become hot enough for carbon nuclei to fuse.

Question 34

As their name implies, all planetary nebulae feature spherical shells and look like the disks of Uranus or Neptune.

Question 35

The nova event is created by the helium flash.

Question 36

The formation of carbon requires a core temperature of about 100 million K, but iron takes much higher temperatures and pressures.

Question 37

While there are none yet, in the very distant future, most normal matter will be in the form of black dwarfs.

Question 38

Like emission nebulae, planetary nebulae glow because hot stars are causing the gases to ionize when exposed to strong ultraviolet radiation.

Question 39

A white dwarf's atoms have their electron orbitals crushed as closely as the Exclusion Principle allows.

Question 40

Elements heavier than iron are formed mainly in supernovae.

Question 41

Because they all involve the detonation of a carbon- rich white dwarf at the Chandrasekhar limit, all Type I supernovae are approximately equally luminous.

Question 42

Novae are more closely related to Type II than to Type I supernovae.

Question 43

Supernova 1987A was the first supernova observed by astronomers since Galileo first turned a telescope to the heavens.

Question 44

Type II supernova spectra are poor in hydrogen because stars that explode this way use up all their hydrogen before they leave the main sequence.

Question 45

While luminous enough to be seen with the naked eye, Supernova 1987A was, in fact, in our companion galaxy, the Large Magellanic Cloud.

Question 46

A massive star can fuse only up to the element silicon in its core.

Question 47

Neutrinos can move faster than c, the speed of light, as was discovered in SN1987A in 1987.

Question 48

A star system can become a Type I supernova several times.

Question 49

Chandrasekhar's limit is 1.4 times the mass of our Sun.

Question 50

Most of the energy released during a supernova is emitted as neutrinos.

Question 51

A 100 million- year- old open cluster will no longer contain any O- type stars.

Question 52

The number of Type I and Type II supernovae observed are approximately equal.

Question 53

A carbon- detonation supernova starts out as a white dwarf in a close binary system.

Question 54

The helium flash is followed within a few million years by the Type II supernova.

Question 55

If a white dwarf gains enough mass from a nearby star to exceed its Chandrasekhar limit it will become a nova.

Question 56

Our Sun will likely die as a Type I supernova in about five billion years.

Question 57

Because they all involve formation of iron in the cores of massive stars, all Type II supernovae are approximately equally luminous.

Question 58

Supergiant stars are burning different fuels in several shells around the core.

Question 59

Gold is rare since the only time it can be formed is during a supernova.

Question 60

Novae and Type II supernovae are essentially the same phenomena.

Question 61

When a low mass star first runs short of hydrogen in its core, it becomes brighter because

A) its outer, cooler layers are shed, and we see the brighter central core.
B) the helium flash increases the size of the star immensely.
C) the core contracts, raising the temperature and extending the hydrogen burning shell outward.
D) it explodes as a nova.
E) helium fusion gives off more energy than does hydrogen.

Question 62

The helium flash converts helium nuclei into

A) iron.
B) carbon.
C) oxygen.
D) boron.
E) beryllium.

Question 63

What temperature is needed to fuse helium into carbon?

A) 5,800 K
B) 100,000 K
C) 15 million K
D) 100 million K
E) one billion K

Question 64

A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object?

A) nova
B) black dwarf
C) brown dwarf
D) Type I supernova
E) Type II supernova

Question 65

Supernova 1987A matched the theoretical predictions for Type I supernovae well.

Question 66

A white dwarf has the mass of the Sun and the volume of

A) Earth.
B) the Moon.
C) Mars.
D) Jupiter.
E) Eros.

Question 67

During the hydrogen shell burning phase

A) the star remains at the same luminosity it had before.
B) the core is expanding.
C) the star becomes less luminous.
D) hydrogen is burning in the central core.
E) the star grows more luminous.

Question 68

A star (no matter what its mass) spends most of its life

A) as a protostar.
B) as a red giant or supergiant.
C) as a planetary nebula.
D) as a main- sequence star.
E) as a T- Tauri variable star.

Question 69

Which of these is true of planetary nebulae?

A) They are the material which causes the eclipses in eclipsing binary systems.
B) They are ejected envelopes surrounding a highly evolved low- mass star.
C) They are expelled by the most massive stars in their final stages before supernova.
D) They are rings of material around protostars that will accrete into planets in time.
E) They are the envelopes that form when blue stragglers merge.

Question 70

Blue stragglers are among the first stars formed in a cluster.

Question 71

The spectra of the oldest stars show the most heavy elements.

Question 72

The blue stragglers represent the horizontal branch for globular clusters.

Question 73

A solar- mass star will evolve off the main sequence when

A) it completely runs out of hydrogen.
B) it explodes as a violent nova.
C) it builds up a core of inert helium.
D) it expels a planetary nebula to cool off and release radiation.
E) it loses all its neutrinos, so fusion must cease.

Question 74

A star is on the horizontal branch of the H- R diagram. Which statement is true?

A) It is about to experience the helium flash.
B) It is burning both hydrogen and helium.
C) It is burning only helium.
D) The star is contracting.
E) The star is about to return to the main sequence.

Question 75

A(n) represents a relatively peaceful mass loss as a red giant becomes a white dwarf.

A) supernova
B) supernova remnant
C) planetary nebula
D) nova
E) emission nebula

Question 76

Can a star become a red giant more than once?

A) no, or we would see them as the majority of naked- eye stars
B) no, it will lose so much mass as to cross the Chandrasekhar Limit
C) yes, before and after the helium flash
D) yes, before and after the Type II supernova event
E) no, the planetary nebula blows off all the outer shells completely

Question 77

Compared to our Sun, a typical white dwarf has

A) a smaller mass and half the density.
B) a larger mass and a hundred times lower density.
C) about the same mass and a million times higher density.
D) about the same mass and density.
E) a smaller mass and twice the density.

Question 78

Globular clusters are dominated by bright red supergiants at the top right of the H- R diagram.

Question 79

When a star's inward gravity and outward pressure are balanced, the star is said to be

A) in gravitational collapse.
B) in rotational equilibrium.
C) in hydrostatic equilibrium.
D) in thermal expansion.
E) a stage 2 protostar.

Question 80

The outward pressure in the core of a red giant balances the inward pull of gravity when

A) the electrons and protons have combined to form neutrons.
B) hydrogen begins fusing into helium.
C) iron forms in the inner core.
D) carbon fuses into heavier elements.
E) the electron orbits are compressed so much they are all in contact.