Deck 19: The Evolution of Stars

Question 1

The main sequence lifetime of an O star compared with an M star is

A)Much longer because there is more fuel available
B)Much shorter because the O star burns fuel at a much faster rate.
C)About the same because all stars live about 10 billion years.
D)Much shorter because there is much less hydrogen in O stars

Answer 1

Much shorter because the O star burns fuel at a much faster rate.

Question 2

Estimate the main sequence lifetime for a star that is twice as massive as the Sun and 8 times as luminous.

A)16 times the Sun's main sequence lifetime
B)One-quarter the Sun's main sequence lifetime
C)One-eighth the Sun's main sequence lifetime
D)Twice the Sun's main sequence lifetime

Answer 2

One-quarter the Sun's main sequence lifetime

Question 3

A two solar mass star has about 2 times the Sun's supply of nuclear energy.Its luminosity is 10 times that of the Sun.How does the lifetime of the star compare with that of the Sun?

A)2 times longer
B)The same
C)One-fifth as long
D)One-tenth as long

Answer 3

One-fifth as long

Question 4

The least massive stars in which nuclear fusion occurs have masses of about 8% that of the Sun.Why don't less massive objects ever experience nuclear fusion?

A)They explode before fusion can begin
B)They collide with other objects and increase their masses
C)They never become hot enough for fusion to occur
D)They become black holes before fusion can begin

Question 5

Massive stars on the upper end of the main sequence generate energy by means of the

A)Proton-proton cycle
B)CNO cycle
C)Triple alpha reaction
D)Radiation reaction

Question 6

Which of the following cannot be assumed about the stars in a given cluster?

A)They are all nearly the same distance from us
B)They all had the same initial chemical composition
C)They all have the same age
D)They all have the same mass

Question 7

The main sequence turnoff of a cluster of stars is a good indicator of which of the following properties of the cluster?

A)Age
B)Number of stars in the cluster
C)Chemical composition
D)Distance

Question 8

When a star is just evolving off the main sequence,which element is most common in the core?

A)Hydrogen
B)Helium
C)Carbon
D)Iron
E)Depends on spectral type

Question 9

Carbon,hydrogen,and helium can all be used a fuels during the career of a massive star.Which of the following gives these elements in the correct order in which they will be consumed in the star?

A)Hydrogen,helium,carbon
B)Helium,carbon,hydrogen
C)Carbon,hydrogen,helium
D)Hydrogen,carbon,helium

Question 10

An evolutionary track describes the career of a star by showing changes in its location in

A)Space
B)An H-R diagram
C)A mass-luminosity diagram
D)A mass-radius diagram

Question 11

If M is the mass of a star and L is its luminosity,which of the following is proportional to the main sequence lifetime of a star?

A)M / L
B)M * L
C)M - L
D)M + L

Question 12

Which of the following occurs just after a star like the Sun exhausts the hydrogen in its core?

A)The core contracts,the outer layers contract
B)The core contracts,the outer layers expand
C)The core expands,the outer layers contract
D)The core expands,the outer layers expand
E)It becomes a supernova

Question 13

Cluster A has no stars of spectral type O,B,and A on its main sequence,whereas cluster B has stars of all types but O on its main sequence.Which of the following correctly describes the relative ages of clusters A and B?

A)The above information is insufficient to determine the relative ages
B)Both clusters are older than the Sun
C)Cluster A is older than B
D)Cluster B is older than A

Question 14

What do all main sequence stars have in common?

A)They are all the same age
B)They are all consuming hydrogen in their cores
C)They all have the same mass
D)They all have convective cores.

Question 15

What is the general name for a star that is converting hydrogen into helium in its core?

A)Main sequence star
B)Red giant star
C)White dwarf star
D)Protostar

Question 16

The age of a cluster can be estimated by

A)Observing the number of stars-larger numbers imply older cluster
B)Observing the number of stars-larger numbers imply younger cluster
C)Plotting the stars on an HR diagram-lower turnoff implies younger
D)Plotting the stars on an HR diagram-lower turnoff implies older
E)Plotting the stars on a color-color diagram-lower values imply older

Question 17

Based on your knowledge of the H-R diagram,which of the descriptions of a star cluster is astrophysical nonsense?

A)A complete main sequence with no red giants and no white dwarfs
B)A complete main sequence except no O stars,there are some red giants
C)A complete main sequence,no red giants but a large number of white dwarfs
D)No stars of spectral classes O,B,or A,but red giants and white dwarfs

Question 18

All the stars in a cluster are usually assumed to have the same

A)Age
B)Mass
C)Temperature
D)Main sequence lifetime

Question 19

As soon as its core hydrogen is exhausted,a star like the Sun begins to evolve

A)Toward the upper right in the H-R diagram
B)Toward the zero age main sequence stage
C)Up the main sequence to become an O star
D)Toward the lower left in the H-R diagram

Question 20

The most important factor affecting a star's main-sequence lifetime is

A)Radius
B)Mass
C)Chemical composition
D)Surface temperature

Question 21

The sequence of reactions by which stars convert helium into carbon is called the

A)S-process
B)Triple alpha reaction
C)CNO cycle
D)Proton-proton chain

Question 22

What is the triple alpha process?

A)A fraternity initiation ceremony
B)A pair of reactions that fuses helium into carbon
C)The mechanism that forms triple star systems
D)A situation in which all three energy transport mechanisms work at once

Question 23

What happens when electrons become degenerate?

A)Their pressure becomes independent of temperature
B)They are converted to neutrons
C)They become extremely hot
D)They form a crystalline lattice

Question 24

Which of the following is a key difference between the pressure in a normal gas and in a degenerate gas?

A)In a degenerate gas,pressure doesn't depend on temperature
B)In a degenerate gas,pressure doesn't depend on density
C)Degenerate pressure exists whether matter is present or not
D)In a degenerate gas pressure varies rapidly with time

Question 25

One reason that Cepheid stars are important to astronomers is that

A)They are especially rich in metal content
B)There is a definite relationship between variability period and luminosity
C)They are all in the plane of the galaxy-so center can be measured
D)They can be seen even in distant clusters of galaxies
E)They are very young,so stellar evolution can be studied in detail

Question 26

Elements heavier than iron are produced

A)In stars during hydrogen burning
B)In interstellar space
C)During supernova outbursts
D)During carbon burning in massive stars

Question 27

What prevents stars of 4 solar masses from exploding as supernovae?

A)Winds strip away their outer layers
B)They become white dwarfs first
C)They become black holes first
D)They have such long main sequence lifetimes that this has never happened

Question 28

What causes Cepheid variables to vary in brightness?

A)They pulsate
B)Eclipses
C)Changes in nuclear energy generation rate
D)Obscuration by clouds of dust

Question 29

What would happen if asymptotic giant branch stars didn't shed their outer layers into interstellar space?

A)More of them would become supernovas
B)They would become black holes more quickly
C)The mass of the galaxy would be greater
D)There would be more star formation going on in the galaxy

Question 30

What element is produced by the triple-alpha reaction,in which three helium nuclei are fused together?

A)Hydrogen
B)Carbon
C)Iron
D)Uranium

Question 31

The "helium flash" is

A)The rapid consumption of core helium when helium fusion first starts in a star
B)A flash of light as the star encounters a cloud of helium
C)A bright X-ray flash from a helium accretion disk surrounding a black hole
D)An infrared burst from helium-rich proto stars

Question 32

The lifetime of a star half the mass of the Sun has what relationship to our Sun's lifespan?

A)The star's lifespan is shorter than that of our Sun.
B)The star's lifespan is longer than that of our Sun.
C)The star's lifespan is the same as that of our Sun because mass does not affect the lifetime.
D)More information is required to answer the question.

Question 33

What limits the formation of giant stars of extremely large sizes?

A)Fusion pressures get larger as the size of the star grows,eventually blowing the star into smaller pieces.
B)Heavy elements in the core exert an outward pressure,preventing the formation of a large core.
C)Gas pressure from the outer layers of the star blow the star apart.
D)The core collapses suddenly,causing an explosion before the core can form.

Question 34

A planetary nebula is produced by

A)A supernova explosion
B)The dust left over when a cluster of stars forms
C)The gradual loss of its outer layers by a dying star
D)A nova explosion

Question 35

When a superwind strips away the outer layers of a star,the resulting shell of expanding gas becomes visible as

A)A planetary nebula
B)An HII region
C)A reflection nebula
D)A dark nebula

Question 36

The fusion of iron nuclei does not occur in stable stars.Why not?

A)Iron isn't a stable element.
B)The fusion process skips over iron and goes on to more massive elements.
C)Iron fusion uses up energy instead of producing energy
D)Iron is destroyed in stars as soon as it is produced