Deck 13: Star Stuff

Question 1

This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. What will happen to the star after stage viii?

A)It will continue to expand gradually until carbon fusion begins in its core.
B)It will explode as a supernova and leave a neutron star or black hole behind.
C)It will remain in stage viii for about 10 billion years, after which its outer layers will shrink back and cool.
D)Its outer layers will be ejected as a planetary nebula and its core will become a white dwarf.

Answer 1

D

Question 2

(Use diagram of abundance vs atomic number)What process best explains the observed pattern of abundances of elements with atomic numbers between 6 and 20?

A)radioactive decay of nuclei with odd numbers of protons
B)fusion reactions with helium nuclei
C)fusion reactions with hydrogen nuclei
D)fusion reactions with neutrons

Answer 2

B

Question 3

Why is Supernova 1987A particularly important to astronomers?

A)It provided the first observational evidence that supernovae actually occur.
B)It was the nearest supernova detected in nearly 400 years.
C)It occurred only a few dozen light- years from Earth.
D)It was the first supernova detected in nearly 400 years.
E)It provided the first evidence that neutron stars exist.

Answer 3

B

Question 4

No stars are expected with masses greater than 150 times our Sun because

A)they would fragment into binary stars because of their rapid rotation.
B)they would generate so much power that they would blow themselves apart.
C)they would be too massive for hydrogen fusion to occur in their cores.
D)they would shine exclusively at X- ray wavelengths and would be difficult to detect.
E)molecular clouds do not have enough material to form such massive stars.

Question 5

The main source of energy for a star as it grows in size to become a red giant is _ _.

A)hydrogen fusion in a shell surrounding the central core
B)hydrogen fusion in the central core
C)gravitational contraction
D)helium fusion in the central core

Question 6

According to this plot, which is the third most abundant element in the universe?

A)helium
B)oxygen
C)hydrogen
D)boron
E)lithium

Question 7

Approximately what core temperature is required before hydrogen fusion can begin in a star?

A)10 billion K
B)10 trillion K
C)1 billion K
D)10 million K
E)10,000 K

Question 8

This schematic shows the number of stars formed in each mass range for each star more massive than 10 MSun. What is the mass range of the most common stars?

A)0)08 - 0.5 MSun
B)10 - 150 MSun
C)2 - 10 MSun
D)0)5 - 2 MSun

Question 9

As a solar mass protostar moves on to the main sequence,

A)its surface temperature and luminosity increase.
B)its surface temperature decreases and its luminosity increases.
C)its surface temperature and luminosity decrease.
D)its surface temperature and luminosity remain the same.
E)its surface temperature increases and its luminosity decreases.

Question 10

What did Carl Sagan mean when he said that we are all "star stuff"?

A)that the Earth formed at the same time as the Sun
B)that the carbon, oxygen, and other elements essential to life were created by nucleosynthesis in stellar cores
C)that the universe contains billions of stars
D)that the Sun formed from the interstellar medium: the "stuff" between the stars
E)that life would be impossible without energy from the Sun

Question 11

The ultimate fate of our Sun is to .

A)become a white dwarf that will slowly cool with time
B)become a rapidly spinning neutron star
C)explode in a supernova
D)become a black hole

Question 12

Which statement about this cluster is not true?

A)It is likely to be spherical in shape.
B)It is likely to be located in the halo of the galaxy.
C)It contains some stars that are burning helium in their cores.
D)It is the type of cluster known as an open cluster of stars.
E)It probably contains no young stars at all.

Question 13

Which of the following statements about degeneracy pressure is not true?

A)Degeneracy pressure is a consequence of the laws of quantum mechanics.
B)Degeneracy pressure varies with the temperature of the star.
C)Degeneracy pressure can halt gravitational contraction of a star even when no fusion is occurring in the core.
D)Degeneracy pressure keeps any protostar less than 0.08 solar mass from becoming a true, hydrogen- fusing star.

Question 14

What eventually halts the gravitational collapse of an interstellar gas cloud that forms an object that is massive enough to become a star?

A)the central object becoming hot enough to sustain nuclear fusion in its core
B)nothing; all collapsing gas clouds become black holes
C)a critical fraction of the gas has been driven further into space
D)the crowding of electrons in the core

Question 15

Which type of star spends the longest time as a protostar?

A)M star
B)B star
C)G star
D)O star

Question 16

What percentage of a star's total lifetime is spent on the main sequence?

A)90%
B)10%
C)100%
D)20%
E)50%

Question 17

The vast majority of stars in a newly formed star cluster are .

A)very high- mass, type O and B stars
B)red giants
C)about the same mass as our Sun
D)less massive than the Sun

Question 18

What happens when the gravity of a massive star is able to overcome neutron degeneracy pressure?

A)The core contracts and becomes a black hole.
B)The star explodes violently, leaving nothing behind.
C)The core contracts and becomes a ball of neutrons.
D)Gravity is not able to overcome neutron degeneracy pressure.
E)The core contracts and becomes a white dwarf.

Question 19

Which of the following masses separates low mass stars from high mass stars?

A)about 0.08 solar masses
B)about 1 solar mass
C)about 2 solar masses
D)about 50 solar masses
E)about 150 solar masses

Question 20

What change slowly occurs during the main- sequence lifetime of a star?

A)Its core temperature slowly increases, increasing the fusion rate and hence the luminosity.
B)As hydrogen is used up in the core, the fusion rate decreases and reduces the luminosity.
C)It gathers more gas from interstellar space, increasing its mass and hence the luminosity.
D)As the solar wind blows material into space, the decreasing mass reduces pressure in the core, which in turn reduces the fusion rate and the luminosity.

Question 21

The figure above shows the abundance of elements in the galaxy relative to hydrogen. What is the general trend in elemental abundance?

A)Elements with an odd number of protons are less abundant than neighboring elements.
B)Elements with more protons are less abundant.
C)Elements with an even number of protons are less abundant than neighboring elements.
D)both A and B
E)both A and C

Question 22

Most interstellar clouds remain stable in size because the force of gravity is opposed by within the cloud.

A)thermal pressure
B)stellar winds
C)radiation pressure
D)degeneracy pressure

Question 23

The interstellar clouds called molecular clouds are .

A)the cool clouds in which stars form
B)the hot clouds of gas expelled by dying stars
C)the clouds in which elements such as carbon, nitrogen, and oxygen are made
D)clouds that are made mostly of complex molecules such as carbon dioxide and sulfur dioxide

Question 24

At approximately what temperature can helium fusion occur?

A)100,000 K
B)100 billion K
C)1 million K
D)100 million K
E)10 million K

Question 25

Which element is the dead end for cores of the most massive stars?

A)oxygen
B)hydrogen
C)lead
D)uranium
E)iron

Question 26

What happens to the core of a star after it ejects a planetary nebula?

A)It becomes a neutron star.
B)It contracts from a protostar to a main- sequence star.
C)It becomes a white dwarf.
D)It breaks apart in a violent explosion.
E)None of the above

Question 27

Observations show that elements with atomic mass numbers divisible by 4 (such as oxygen- 16, neon- 20, and magnesium- 24)tend to be more abundant in the universe than elements with atomic mass numbers in between. Why do we think this is the case?

A)Elements with atomic mass numbers divisible by 4 tend to be more stable than elements in between.
B)The apparent pattern is thought to be a random coincidence.
C)At the end of a high- mass star's life, it produces new elements through a series of helium capture reactions.
D)This pattern in elemental abundances was apparently determined during the first few minutes after the Big Bang.

Question 28

What types of stars end their lives with supernovae?

A)all stars that are yellow in color
B)stars that have reached an age of 10 billion years
C)stars that are at least several times the mass of the Sun
D)stars that are similar in mass to the Sun
E)all stars that are red in color

Question 29

What is a planetary nebula?

A)the expanding shell of gas that is no longer gravitationally bound to the remnant of a low- mass star
B)the expanding shell of gas that is left when a white dwarf explodes as a supernova
C)the molecular cloud from which protostars form
D)a disk of gas surrounding a protostar that may form into planets
E)what is left of its planets after a low- mass star has ended its life

Question 30

Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission?

A)oxygen
B)iron
C)silicon
D)hydrogen

Question 31

The luminosity of light emerging from the star's gaseous surface is equal to the

A)mass of the star.
B)star's lifetime.
C)rate of energy generated from nuclear reactions in the star's core.
D)temperature of the star's core.
E)star's apparent brightness.

Question 32

The figure above shows the abundance of elements in the galaxy relative to hydrogen. Why does iron have a higher abundance than nearby elements?

A)It has a higher density than other elements, and thus becomes locked away in dust.
B)It is the end product of core fusion in massive stars, and can only be destroyed in rare supernova fusion reactions.
C)It does not; this apparent higher abundance is due to iron's many spectral lines making it easier to find.

Question 33

Suppose that the star Betelgeuse (the upper left shoulder of Orion)were to supernova tomorrow (as seen here on Earth). What would it look like to the naked eye?

A)Because the supernova destroys the star, Betelgeuse would suddenly disappear from view.
B)We'd see a cloud of gas expanding away from the position where Betelgeuse used to be. Over a period of a few weeks, this cloud would fill our entire sky.
C)Betelgeuse would remain a dot of light, but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime.
D)Betelgeuse would suddenly appear to grow larger in size, soon reaching the size of the full Moon. It would also be about as bright as the full Moon.

Question 34

Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true?

A)All the stars in the cluster will be of about the same mass.
B)All the stars in the cluster will have approximately the same luminosity and surface temperature.
C)All the stars in the cluster will become main- sequence stars at about the same time.
D)A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage.

Question 35

What is the lifetime of a star of 0.1 solar masses and a luminosity of 0.01 that of the Sun? Assume the lifetime of the Sun is 10 billion years.

A)100 billion years
B)10 trillion years
C)10 billion years
D)10 million years
E)This star will never start hydrogen fusion reactions because it is not massive enough.

Question 36

Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, and so on)in a high- mass star is not true?

A)Each successive stage lasts for approximately the same amount of time.
B)As each stage ends, the core shrinks and heats further.
C)As each stage ends, the reactions that occurred in previous stages continue in shells around the core.
D)Each successive stage creates an element with a higher atomic number and atomic mass number.

Question 37

Why don't low- mass stars have the CNO cycle occurring in their cores?

A)Their core temperatures are too low.
B)The CNO cycle makes elements heavier than carbon, nitrogen, and oxygen.
C)They don't have enough carbon, nitrogen, and oxygen.

Question 38

At the end of its life, the remaining core of this star will be left behind as

A)a black hole.
B)a supernova.
C)a white dwarf made primarily of silicon and iron.
D)a white dwarf made primarily of carbon and oxygen.
E)a neutron star.

Question 39

What happens when a star like the sun exhausts its core hydrogen supply?

A)It expands, becoming bigger but dimmer.
B)Its core contracts, but its outer layers expand and the star becomes bigger and brighter.
C)It contracts, becoming hotter and brighter.
D)It contracts, becoming smaller and dimmer.
E)Its core contracts, but its outer layers expand and the star becomes bigger but cooler and therefore remains at the same brightness.

Question 40

If someone somehow added a lot more hydrogen and helium to the Sun (say 50% more than it has now), what would happen to it?

A)It would cease to exist as a star because it would be too diffuse and fluffy.
B)It would increase in size and float away.
C)It would begin to evolve much more quickly than it is now.
D)It would explode as a supernova.
E)Its nuclear reactions would slow down because its heavy element abundance would be relatively less.

Question 41

Suppose the star Betelgeuse (the upper left shoulder of Orion)were to become a supernova tomorrow (as seen here on Earth). What would it look like to the naked eye?

A)Betelgeuse would remain a dot of light but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime.
B)Betelgeuse would suddenly appear to grow larger in size, soon reaching the size of the full moon. It would also be about as bright as the full moon.
C)Because the supernova event destroys the star, Betelgeuse would suddenly disappear from view.
D)We'd see a cloud of gas expanding away from the position where Betelgeuse used to be. Over a period of a few weeks, this cloud would fill our entire sky.

Question 42

Consider the star to which the arrow points. Which of the following statements about this star is not true?

A)Its core temperature is higher than the Sun's.
B)It is larger in radius than the Sun.
C)Its surface temperature is lower than the Sun's.
D)It is significantly less massive than the Sun.
E)It is brighter than the Sun.

Question 43

Most interstellar dust grains

A)are produced in the cores of low- mass stars
B)are produced in supernova explosions.
C)are produced in the atmospheres of red giant stars.
D)were produced in the Big Bang.
E)are produced in the interstellar medium.

Question 44

Which of the following properties describes a low- mass star?

A)has higher main- sequence luminosities than high mass stars
B)ends its life as a supernova
C)late in life, fuses carbon into oxygen
D)has longer lifetimes than high mass stars

Question 45

Which part of the electromagnetic spectrum generally gives us our best views of stars forming in dusty clouds?

A)visible light
B)infrared
C)blue light
D)ultraviolet

Question 46

What is the approximate range of masses that newborn main sequence stars can have?

A)0)1 to 10 solar masses
B)0)001 to 150 solar masses
C)0)1 to 1,000 solar masses
D)0)1 to 150 solar masses
E)0)001 to 10 solar masses

Question 47

Why is Supernova 1987A particularly important to astronomers?

A)It was the first supernova detected in nearly 400 years.
B)It occurred only a few light- years from Earth.
C)It provided the first evidence that supernovae really occur.
D)It is the nearest supernova to have occurred at a time when we were capable of studying it carefully with telescopes.

Question 48

The figure above shows the abundance of elements in the galaxy relative to hydrogen. What is the least abundant of the elements with an atomic number less than iron's?

A)beryllium
B)hydrogen
C)nitrogen
D)lithium

Question 49

This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. During which stage is the star's energy supplied by primarily by gravitational contraction?

A)vi
B)viii
C)ii
D)v
E)iii

Question 50

After a supernova explosion, the remains of the stellar core .

A)will always be a black hole
B)will always be a neutron star
C)may be either a neutron star or a black hole
D)may be either a white dwarf, neutron star, or black hole

Question 51

What can trigger the gravitational collapse of an interstellar gas cloud?

A)a decrease in temperature
B)an increase in density
C)a rise in temperature
D)A and B
E)A and C

Question 52

Which event marks the beginning of a supernova?

A)the sudden collapse of an iron core into a compact ball of neutrons
B)the sudden initiation of the CNO cycle
C)the onset of helium burning after a helium flash
D)the beginning of neon burning in an extremely massive star

Question 53

Compared to the star it evolved from, a white dwarf is

A)cooler and brighter.
B)hotter and dimmer.
C)hotter and brighter.
D)the same temperature and brightness.
E)cooler and dimmer.

Question 54

How are elements beyond iron formed in massive- star supernovae?

A)Neutrons produced during the core collapse are slammed into atomic nuclei.
B)Elements thrown out at high speeds fuse with hydrogen atoms in the interstellar medium.
C)The high temperature and pressure allow iron nuclei to fuse.

Question 55

How many helium nuclei fuse together when making carbon?

A)3
B)4
C)2
D)It varies depending on the reaction.
E)Helium cannot fuse into carbon.

Question 56

You discover a binary star system in which one star is a 15 MSun main- sequence star and the other is a 10 MSun giant. How do we think that a star system such as this might have come to exist?

A)The giant must once have been the more massive star, but is now less massive because it transferred some of its mass to its companion.
B)The two stars are simply evolving normally and independently, and one has become a giant before the other.
C)The two stars probably were once separate, but became a binary when a close encounter allowed their mutual gravity to pull them together.
D)Although both stars probably formed from the same clump of gas, the more massive one must have had its birth slowed so that it became a main sequence stars millions of years later than its less massive companion.

Question 57

Why do flat disks form around young stars?

A)They don't; the stars form from the disks.
B)Centrifugal force pushes gas outward from the spinning gas cloud.
C)Intense winds from nearby massive stars flatten the gas cloud.
D)Collisions between rotating gas particles flatten the gas cloud along the axis of rotation.

Question 58

Which of the following sequences correctly describes the stages of life for a low- mass star?

A)white dwarf, main- sequence, red giant, protostar
B)protostar, red giant, main- sequence, white dwarf
C)red giant, protostar, main- sequence, white dwarf
D)protostar, main- sequence, white dwarf, red giant
E)protostar, main- sequence, red giant, white dwarf

Question 59

What can we learn about a star from a life track on an H- R diagram?

A)how the star's distance from Earth varies at different times in its life
B)the star's age
C)the star's current stage of life
D)the surface temperature and luminosity the star will have at each stage of its life

Question 60

Consider the star to which the arrow points. How is it currently generating energy?

A)by hydrogen shell burning around an inert helium core
B)by gravitational contraction
C)by both hydrogen and helium shell burning around an inert carbon core
D)by core hydrogen fusion
E)by core helium fusion combined with hydrogen shell burning

Question 61

What star is the most likely to have made the atoms of gold in your jewelry or your electronics?

A)the Sun
B)a white dwarf
C)a low- mass star
D)a high- mass star

Question 62

Which of the following phenomena is not commonly associated with the star formation process?

A)intense ultraviolet radiation coming from a protostar
B)strong winds of particles blowing out into space from a protostar
C)powerful "jets" shooting out along the rotation axis of a protostar
D)the formation of a spinning disk of material around a protostar

Question 63

Which of the following lists the stages of life for a low- mass star in the correct order?

A)protostar, main- sequence star, red giant, planetary nebula, white dwarf
B)protostar, main- sequence star, planetary nebula, red giant
C)protostar, main- sequence star, red giant, supernova, neutron star
D)main- sequence star, white dwarf, red giant, planetary nebula, protostar

Question 64

After a supernova event occurring in a high- mass star, what is left behind?

A)always a black hole
B)always a neutron star
C)always a white dwarf
D)either a white dwarf or a neutron star
E)either a neutron star or a black hole

Question 65

Which event marks the beginning of a supernova?

A)the sudden collapse of an iron core into a compact ball of neutrons
B)the onset of helium burning after a helium flash in a star with mass comparable to that of the Sun
C)the beginning of neon burning in an extremely massive star
D)the sudden outpouring of X- rays from a newly formed accretion disk
E)the expansion of a low- mass star into a red giant

Question 66

This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. During which stage does the star have an inert (non- burning)carbon core surrounded by shells of helium and hydrogen burning?

A)vi
B)viii
C)ii
D)iv
E)iii

Question 67

Which process is required to allow a gravitationally- collapsing gas cloud to continue to collapse?

A)The cloud must collide with other clouds.
B)The cloud must radiate much of its thermal energy.
C)The cloud must trap most of its thermal energy.
D)New dust particles must continually be made in the cloud.

Question 68

Why does stellar main- sequence lifetime decrease with increasing stellar mass?

A)It doesn't; higher mass stars have more hydrogen available for fusion, and thus have longer lifetimes.
B)Higher outward pressure prevents the core hydrogen from being replenished by the star's outer layers.
C)Higher core temperatures cause fusion to proceed much more rapidly.
D)Strong stellar winds cause higher mass stars to lose mass quickly.

Question 69

Which star spends the longest time in the protostellar phase of life?

A)a 1 solar mass star
B)a 2 solar mass star
C)a 3 solar mass star
D)a 4 solar mass star
E)a 5 solar mass star

Question 70

What is the source of luminosity for protostars that have not yet become hot enough for fusion in their cores?

A)fusion in their low- density outer layers
B)light absorbed from nearby stars
C)energy released by infalling matter
D)fission from concentrated radioactive elements

Question 71

What kind of gas cloud is most likely to give birth to stars?

A)a cold, low- density gas cloud
B)a cold, dense gas cloud
C)a hot, low- density gas cloud
D)a hot, dense gas cloud

Question 72

Where would a brown dwarf be located on an H- R diagram?

A)in the lower left corner of the H- R diagram
B)below and to the right of the lowest part of the main sequence
C)above and to the left of the highest part of the main sequence
D)in the upper right corner of the H- R diagram

Question 73

In order to predict whether a star will eventually fuse oxygen into a heavier element, you mainly want to know what fact about the star?

A)its luminosity
B)how much oxygen it now has in its core
C)its mass
D)its overall abundance of elements heavier than helium

Question 74

Where does gold (the element)come from?

A)It is produced by mass transfer in close binaries.
B)It is produced during the late stages of fusion in low- mass stars.
C)It was produced during the Big Bang.
D)It is produced during the supernova explosions of high- mass stars.

Question 75

Which of the following statements about brown dwarfs is not true?

A)Brown dwarfs are supported against gravity by degeneracy pressure, which does not depend on the object's temperature.
B)Brown dwarfs form like ordinary stars but are too small to sustain nuclear fusion in their cores.
C)All brown dwarfs have masses less than about 8% that of our Sun.
D)Brown dwarfs eventually collapse to become white dwarfs.

Question 76

What is a helium flash?

A)the sudden onset of helium fusion in the core of a low- mass star
B)another name for the helium fusion reaction
C)a sudden brightening of a low- mass star, detectable from Earth by observing spectral lines of helium
D)the ignition of helium shell burning in a high- mass star with a carbon core

Question 77

Identify the correct sequence of life events for a high mass star.

A)red supergiant, main sequence, neutron star, supernova
B)red supergiant, main sequence, supernova, neutron star
C)main sequence, red supergiant, neutron star, supernova
D)main sequence, red supergiant, supernova, neutron star

Question 78

Why are elements with even numbers of protons more abundant, on average, than elements with odd numbers of protons?

A)because elements are mainly made in fusion reactions with helium nuclei
B)because elements are mainly made in fusion reactions with hydrogen nuclei
C)because when elements split in a fission reaction, they prefer to split with all the protons paired
D)There's no explanation; it's something of a mystery to be explained or it may be a coincidence.

Question 79

Which of the following statements about the stages of nuclear burning in a massive star is not true?

A)Each successive stage lasts for approximately as long as the first, hydrogen fusion stage.
B)Each successive stage of fusion requires higher temperatures than the previous stages.
C)As each stage ends, the core shrinks further.
D)Each successive stage creates an element with a higher atomic weight.

Question 80

When does a protostar become a main- sequence star?

A)at the instant that the first hydrogen fusion reactions occur in the protostar's core
B)when it becomes luminous enough to emit thermal radiation
C)when a piece of a molecular cloud first begins to contract into a star
D)when the rate of hydrogen fusion becomes high enough to balance the rate at which the star radiates energy into space