Chapter 10 Flashcards
With respect to main-sequence stars and stellar evolution, select all of the correct statements from the following list.
Since the interiors of stars cannot be observed, there are no theories about their structure.
More massive stars live longer; they take longer to use up all their energy.
Energy flow in a star is a balance between what comes in and what goes out.
Stars change position on the main sequence throughout their lives.
Outward energy flow in a star is by conduction only.
More massive stars are hotter and brighter.
The weight of a star must be balanced by internal pressure.
Stars change position on the main sequence throughout their lives.
Outward energy flow in a star is by conduction only.
More massive stars are hotter and brighter.
The weight of a star must be balanced by internal pressure.
With respect to post main-sequence evolution of stars, select all of the correct statements from the following list.
Moving to the right on the H-R diagram indicates only that the star has cooled, nothing else.
The cores of main-sequence stars begin to collapse when they exhaust their hydrogen.
After leaving the main sequence, most stars move to the right on the H-R diagram.
The helium flash causes a red giant star to go supernova.
More massive stars will fuse the helium in their cores into heavier elements.
Because of the core contraction, the temperature of a star will increase when the hydrogen fuel is exhausted.
After exhausting its hydrogen fuel, a main-sequence star will become a very large, low-density star.
The cores of main-sequence stars begin to collapse when they exhaust their hydrogen.
After leaving the main sequence, most stars move to the right on the H-R diagram.
More massive stars will fuse the helium in their cores into heavier elements.
After exhausting its hydrogen fuel, a main-sequence star will become a very large, low-density star.
With respect to the evolution of star clusters, select all of the correct statements from the following list.
Stars in globular clusters tend to be older than those in open clusters.
The turnoff point is when stars in a cluster begin to no longer shine.
All stars in a cluster are about the same age.
Stars in globular clusters tend to be helium-poor.
Open clusters have more stars than globular clusters.
The age of a cluster can be determined by where the stars are leaving the main sequence.
The less massive stars in a cluster leave the main sequence first.
Stars in globular clusters tend to be older than those in open clusters.
All stars in a cluster are about the same age.
The age of a cluster can be determined by where the stars are leaving the main sequence.
With respect to stellar evolution, select all of the correct statements from the following list.
Variable stars are expanding and contracting.
The period of some Cepheid variables actually changes.
More massive stars will vary their brightness more quickly.
When getting dimmer, variable stars are releasing energy; when getting brighter they are storing energy.
Despite their variability, variable stars stay in a specific position on the H-R diagram.
A changing period in a Cepheid variable means that the size of the star is changing and that the star is therefore evolving.
Only stars on the instability strip are variable.
Variable stars are expanding and contracting.
The period of some Cepheid variables actually changes.
A changing period in a Cepheid variable means that the size of the star is changing and that the star is therefore evolving.
Only stars on the instability strip are variable.
In the model shown above, what fraction of the sun’s mass is hotter than 3,000,000 K?
0.97
A typical open cluster contains 850 stars and is 27 pc in diameter. A typical globular cluster contains 1 million stars and is 25 pc in diameter. The average distance between stars will be smaller in which type of cluster?
globular
Which of the following is NOT considered in making a simple stellar model?
magnetic field
According to the figure shown here, what is the approximate radius of the sun’s nuclear fusion zone?
0.30 solar radii
Why is there a lower mass limit of 0.08 solar masses for main-sequence stars?
Objects below this mass are not hot enough to fuse normal hydrogen.
Why is there an upper mass limit for main-sequence stars of about 100 solar masses?
Objects above this mass fuse hydrogen too rapidly and cannot stay together.
This diagram shows the main-sequence lifetimes of stars with 1, 3, and 15 solar masses. Using this figure, what is the estimated main-sequence lifetime of a spectral type F0 star that has a mass of 1.7 solar masses?
3 billion years
Why are lower main-sequence stars more abundant than upper main-sequence stars?
More low-mass main-sequence stars are formed in molecular clouds and lower main-sequence stars have much longer lifetimes than upper main-sequence stars.
Why does a star’s life expectancy depend on mass?
Mass determines the amount of fuel a star has for fusion and determines the rate of fuel consumption for a star.
Which of the following observable properties of a main-sequence star is a direct indication of the rate at which energy is produced inside that star?
luminosity
Why does an expanding giant star become cooler?
Energy is absorbed in expanding and lifting the gas.
Of the following, which main-sequence star has a longer life expectancy than the sun?
spectral type K2
How does the main-sequence lifetime of a star compare to its entire fusion lifetime?
Stars spend about 90% of their fusion lifetimes on the main sequence.
Why does an expanding giant star become more luminous?
More energy is produced in the interior.
What increases the temperature of an inert helium core inside a giant star?
gravitational contraction
How much longer will the sun last?
about 5 billion years
This figure shows the post-main-sequence evolution of different stars on the H-R diagram. When the sun leaves the main sequence to become a giant, what happens to its surface temperature and luminosity?
The luminosity increases and the surface temperature decreases.
Why will a helium flash never occur in some stars?
Some stars do not develop degenerate helium cores.
Why are lower-mass stars unable to ignite more massive nuclear fuels such as carbon?
They never get hot enough.
How do star clusters confirm that stars are evolving?
The H-R diagram of a star cluster is missing the upper part of the main sequence.
How are the ages of star clusters related to their turnoff points?
The age of a cluster is the life expectancy of stars at its turnoff point and the higher the turnoff point, the older the star cluster.
What is the general trend in the ages of the two types of star clusters?
Globular clusters are older than open clusters.
From the figure shown here, what is the absolute magnitude of a Type II Cepheid with a period of 20 days?
–2
The period of a Cepheid variable star and the time of one recent maximum can be used to predict the time of a future maximum. Suppose that you calculate the time of future maximum brightness and then make measurements to observe this maximum. After the correction for Earth’s orbital position has been made, you find that the maximum occurred a few minutes later than predicted. What does this tell you about this star?
The star is slowly expanding.
What is the main sequence of the H-R diagram?
All of these choices are correct.
Which is a type of star found on the lower end of the main sequence?
red dwarf
Which is a type of star found on the upper end of the main sequence?
O or B
Which of the following is true for a brown dwarf?
It does not have hydrogen fusion occurring in the core.
Which is true for the mass-luminosity relationship?
It only applies to main-sequence stars.
Which is true for main-sequence stars?
Massive stars are bright.
Why is there a mass-luminosity relationship?
The brightness of a main-sequence star depends on the rate of fusion in the core, which depends on the mass.
Which is true for more massive main-sequence stars?
They live shorter lives than low-mass stars.
Which is true for the mass and life-expectancy of a star?
They are not the only interrelated factors: temperature must be considered too.
Which is not true about expanding stars?
All of these are true.
Why does the surface temperature of an expanding star change?
Since energy on the star’s surface is spread out over more area, it gets cooler.
Why does the luminosity of an expanding star change?
Since the star is getting bigger, it has more area through which to give off energy, so it gets brighter.
What is the helium flash?
the explosion of the core of a star at the beginning of helium fusion
What causes the helium flash?
All of these choices are correct.
Why does the helium flash make it hard for astronomers to understand the later stages of stellar evolution?
All of these choices are correct.
Which is a way that some stars avoid the helium flash?
The core doesn’t get hot enough for helium fusion.
Which is true of giant stars?
They are of very low density.
What is the reason for giant stars having the densities that they do?
They are so large.
What is required for carbon fusion to occur in the core of a star?
All of these choices are correct.
How can you estimate the age of a star cluster?
by its brightest stars
What is the turnoff point of a star cluster?
the location on the H-R diagram where stars are leaving the main sequence
How do star clusters confirm that stars evolve?
by the more massive, brighter stars leaving the main sequence
What is “variable” in a variable star?
All of these choices are correct.
Which “variable” in variable stars confirms that stars evolve?
the period of changes in brightness
Which is true for the H-R diagram of a star cluster that has many hot, blue, luminous stars?
It will have stars over most of the main sequence.
If a star cluster has many hot, blue, luminous stars which of the following is probably correct?
It is young.
The H-R diagram of a star cluster that has many hot, blue, luminous stars will have stars over most of the main sequence and be young in age. What is the reason for this?
Hot, blue, luminous stars do not live long lives
Consider the three H-R diagrams of the star clusters shown above: NGC2264, Pleiades, and M67. The youngest cluster is ________ and has ________ -type stars.
NGC4622; pre-main sequence
Consider the three H-R diagrams of the star clusters shown above: NGC2264, Pleiades, and M67. The oldest cluster is ________ and has ________ -type stars.
M67; red giant
The plot above shows changes in the observed time minus the predicted time of maximum brightness for a Cepheid variable observed over about a century. This happens because the star is _________ because it _________ time.
getting larger; evolves over
Based on the deaths of lower-main-sequence stars, select all of the correct statements from the following list.
Red dwarfs will live for a very long time.
Some stellar cores are too massive to become white dwarfs.
Most stars become white dwarfs.
White dwarfs must still have some nuclear fuel, or they would not be visible.
Some giant stars will lose mass into space and form planetary nebulae.
Red dwarfs become red giants.
The sun will become a giant star that fuses carbon.
Red dwarfs will live for a very long time.
Some stellar cores are too massive to become white dwarfs.
Most stars become white dwarfs.
Some giant stars will lose mass into space and form planetary nebulae.
Based on evolving stars in binary systems, select all of the correct statements from the following list.
If one of the stars in a binary system is a giant, the other must be less massive.
If, in a binary system, mass is transferred to a white dwarf, it could return to the main sequence.
The Algol paradox refers to a variable star in a binary system.
If mass is being transferred in a binary system, it may be detectable.
Lagrangian points are stable points in a two-body system.
Mass can be transferred between the stars in a binary system.
A nova is an exploding star.
If mass is being transferred in a binary system, it may be detectable.
Lagrangian points are stable points in a two-body system.
Mass can be transferred between the stars in a binary system.
Based on the deaths of massive stars, select all of the correct statements from the following list.
Nuclear fusion resulting in the production of iron triggers a supernova explosion.
Transferring mass to a white dwarf could trigger a type Ia supernova.
The Chandrasekhar limit is the maximum mass of a white dwarf.
Supernovae leave behind shells of gas.
The 1987 supernova was a typical type II explosion.
More massive stars have more violent deaths.
A type Ib supernova occurs when a star fuses all of its carbon at once.
Transferring mass to a white dwarf could trigger a type Ia supernova.
The Chandrasekhar limit is the maximum mass of a white dwarf.
Supernovae leave behind shells of gas.
More massive stars have more violent deaths.
What event marks the end of every star’s main-sequence life?
the end of hydrogen fusion in the core
Why can’t the lowest-mass stars become giants?
They are fully convective and never develop a hydrogen shell fusion zone.
Which of the following is true about red dwarfs?
All of these choices are correct.
What observational evidence do we have that stars are losing mass?
All of these choices are correct.
The density of the sun is about 1.4 grams per cubic centimeter. Density is mass divided by volume. The volume of a sphere is proportional to the radius cubed. According to this graph, what is the density of a one-solar-mass spherical white dwarf?
about 3,000,000 grams per cubic centimeter
What type of spectrum does the gas in a planetary nebula produce?
an emission line spectrum
Why are the stars found inside planetary nebulae only at temperatures above 25,000 K?
Planetary nebulae glow due to the ionization of low density gas by a hot interior star.
What happens to white dwarfs as they age?
their surface temperatures decrease and luminosity decreases
Why have no black dwarfs yet been observed in our galaxy?
Our galaxy is too young for any to have formed.
What unusual property do all higher-mass white dwarfs have?
They are smaller than lower-mass white dwarfs.
What prevents gravity from shrinking a white dwarf to a smaller size?
degenerate electrons
Which stars have high rates of mass loss due to intense stellar winds?
All of these choices are correct.
What happens to a star when it becomes a giant if it has a close binary companion?
Matter can be transferred from the giant to the companion.
What can happen to the white dwarf in a close binary system when it accretes matter from the companion giant star?
The white dwarf can ignite the new matter and flare up as a nova and accrete too much matter and detonate as a supernova type Ia.
What evidence do we have that some close binary pairs have merged to become a single giant star?
Some giant stars have rapid rotation.
This diagram illustrates the interior structure of which of the following?
supergiant star
Which type of star eventually develops several concentric zones of active shell fusion?
high-mass stars
Which of the following trends accurately represents the characteristics of the several different fusion zones inside a late-stage high-mass star going from the outer to innermost zone?
temperature decreases and mass of individual nuclei increases
Why can’t massive stars generate energy from iron fusion?
Iron fusion consumes energy.
Which of the following statements accurately describe(s) some observed properties of supernovae type Ia and supernovae type II?
Supernovae type II have hydrogen lines in their spectra and supernovae type Ia are more luminous.
Suppose that you monitor the apparent brightness of a supernova and notice that 50 days after it reached maximum brightness, it has dimmed by 2 magnitudes. Examine the light curves in this figure. Which type of supernova are you most likely observing?
Type II
Which type of supernova leaves NO core remnant?
supernova type Ia
Why do old supernova remnants emit X-rays?
The expanding hot gas collides with the interstellar medium.
Why can’t the lowest-mass stars become giants?
They are not massive enough to fuse helium.
Ultimately a sun-like star will become which of the following?
white dwarf
Why can’t the lowest-mass stars have the same fate as the sun-like stars?
They are not massive enough to collapse to such a high density.
Which is evidence that stars lose mass?
All of these choices are evidence.
Where is mass transfer likely to occur?
a binary system
What kind of spectrum does a planetary nebula produce?
emission
Where does a planetary nebula get its energy to produce a spectrum?
from the white dwarf at its center
As white dwarfs cool, which of the following occurs?
They stay the same size and get dimmer.
What is the approximate mass for white dwarfs?
about a solar mass
Why do white dwarfs have masses approximately equal to the sun?
White dwarfs are the cores of stars that could fuse helium but could not fuse carbon, so they should all be similar mass.
What is the probable next step in a star’s evolution after the white dwarf stage?
black dwarf
How many black dwarfs have been observed in our galaxy?
none
Why have no black dwarfs been observed in our galaxy?
There has not been enough time for these objects to form.
What happens to a star in a close binary system when it becomes a giant?
It loses mass to the other star.
Which is the result of the accumulation of mass in a close binary system igniting the core of a white dwarf?
a nova explosion
Which is the result of a collapsing iron core in a massive star?
a type II supernova
Which is the result of mass transfer pushing a white dwarf over the Chandrasekhar limit and its core collapsing, causing all its carbon to fuse at once?
a type Ia supernova
Which is the result of a massive star losing its outer layers in a binary system?
a type Ib supernova
What is the heaviest element that can be fused in the core of a star?
iron
Why can’t massive stars generate energy from further fusion once iron has been created?
It has the most tightly bound nucleus.
Which spectra contain hydrogen lines?
a type II supernova
The spectra of a type II supernova contain hydrogen lines. What is a reason for this?
All of these choices are reasons.
Why do supernova remnants emit X-rays?
because they are filled with hot gas
What kind of object is pictured in the figure?
a planetary nebula
What kind of star produces the object pictured in the figure?
a medium-mass giant star
How is the object pictured in the figure produced?
a giant star ejecting its outer atmosphere
What will eventually happen to the pictured object?
It will continue to expand and become mixed in with the interstellar medium.
What kind of object is pictured in the figure?
a supernova remnant
What kind of star produces the object pictured in the figure?
a very massive star
About how old do you think is the object pictured in the figure?
at most, a few tens of thousands of years
Which of these elements will appear LAST in the core of a massive star after the main sequence stage via nuclear reactions?
iron
Which of these elements serves as a nuclear “fuel” for the longest time in the life of a star?
hydrogen
Giant vs. Supergiant. A classmate states that a main-sequence star of 0.8 solar mass will evolve into an orange subgiant, then into a larger red giant, and then into a larger and redder supergiant. Which part is incorrect?
Orange subgiant
