Intro to Astronomy Chapter 10 Conceptual Questions
According to the figure shown here, what is the approximate radius of the sun's nuclear fusion zone? 0.90 solar radii 0.70 solar radii 0.10 solar radii 0.30 solar radii 0.50 solar radii
0.30 solar radii
In the model shown above, what fraction of the sun's mass is hotter than 3,000,000 K? 0.97 1.00 0.00097 0.097 0.0097
0.97
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 12 billion years over 15 billion years 750 million years 100 million years
3 billion years
Which is not true about expanding stars? They become more luminous. They become cooler. They get less dense. All of these are true.
All of these are true.
What causes the helium flash? the beginning of helium fusion in the core of a star gas pressure in a star becoming independent of temperature the core of a star becoming degenerate All of these choices are correct.
All of these choices are correct.
What is "variable" in a variable star? its brightness the period of changes in brightness its size All of these choices are correct.
All of these choices are correct.
What is required for carbon fusion to occur in the core of a star? high temperature high pressure high mass All of these choices are correct.
All of these choices are correct.
Why does an expanding giant star become more luminous? Less energy is produced in the interior. More energy is produced in the interior. Less energy is produced in the interior and thermal energy is converted into gravitational energy. Thermal energy is converted into gravitational energy. Less energy is produced in the interior and more energy is produced in the exterior.
More energy is produced in the interior.
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. More low-mass main-sequence stars are formed in molecular clouds. Lower main-sequence stars have much longer lifetimes than upper main-sequence stars. High-mass main-sequence stars lose mass and become lower main-sequence stars. All of these choices are correct.
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.
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 Type I The data do not fit either type of supernova. It could be either depending on the peak magnitude. None of these choices are correct.
Type II
Of the following, which main-sequence star has a longer life expectancy than the sun? spectral type F4 spectral type O5 spectral type A7 spectral type K2 spectral type B9
spectral type K2
This diagram illustrates the interior structure of which of the following? white dwarf red dwarf supergiant star giant star main-sequence star
supergiant star
From the figure shown here, what is the absolute magnitude of a Type II Cepheid with a period of 20 days? -4 -1 -3 -2 -5
-2
What is the main sequence of the H-R diagram? a group of stars ranging from cool and dim to bright and hot where most of the stars are found a group of stars ranging from very massive to very low mass All of these choices are correct.
All of these choices are correct.
What observational evidence do we have that stars are losing mass? All of these choices are correct. the solar wind stellar emission lines at ultraviolet and X-ray wavelengths some absorption lines in the spectra of giant stars are blue shifted the solar wind and stellar emission lines at ultraviolet and X-ray wavelengths
All of these choices are correct.
Which of the following is true about red dwarfs? All of these choices are correct. They never become giants. Helium fusion does not occur in a red dwarf. They never develop a shell of hydrogen fusion. None of the red dwarfs in the universe has grown old enough for fusion to stop.
All of these choices are correct.
Which stars have high rates of mass loss due to intense stellar winds? All of these choices are correct. high-mass stars newly forming stars stars approaching death high-mass and newly forming stars
All of these choices are correct.
Why does the helium flash make it hard for astronomers to understand the later stages of stellar evolution? It limits the reliability of mathematical models used to study stellar evolution. It is a short-lived event. It happens deep inside a star. All of these choices are correct.
All of these choices are correct.
Why does an expanding giant star become cooler? Less energy is produced in the star's interior and more energy is produced in the star's exterior. Energy is absorbed in expanding and lifting the gas. Less energy is produced in the star's interior and energy is absorbed in expanding and lifting the gas. Less energy is produced in the star's interior. More energy is produced in the star's interior.
Energy is absorbed in expanding and lifting the gas.
If a star cluster has many hot, blue, luminous stars which of the following is probably correct? It is old. It is young. It is of medium age. You can't tell its age from this information.
It is young.
What is the general trend in the ages of the two types of star clusters? All star clusters are very old. Globular clusters are older than open clusters. The two types of star clusters have both very young and very old members. Globular clusters are young and open clusters are old. All star clusters are very young.
Globular clusters are older than open clusters.
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? The most massive stars live the longest lives. The presence of one kind of star or another cannot tell you the age of a cluster. Hot, blue, luminous stars do not live long lives Since there are not red giants, the cluster can't be too old.
Hot, blue, luminous stars do not live long lives
Why can't massive stars generate energy from iron fusion? The temperature at their centers never gets high enough. Not enough iron is present. The temperature at their centers never gets high enough and the density at their centers is too low. Iron fusion consumes energy. The density at their centers is too low.
Iron fusion consumes energy.
Which of the following is true for a brown dwarf? It does not have hydrogen fusion occurring in the core. It has a surface temperature of about 2500 K. It is about 100 times as massive as Jupiter. All of these choices are correct.
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. It states that hot stars should be of low mass. It states that dim stars should be massive. None of these choices are correct.
It only applies to main-sequence stars.
Which is true for the H-R diagram of a star cluster that has many hot, blue, luminous stars? It will have stars all over the diagram. It will not have many lower-main-sequence stars. It will have only middle- and upper-main-sequence stars. It will have stars over most of the main sequence.
It will have stars over most of the 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; pre-main sequence M67; red giant Pleiades; pre-main sequence NGC4622; pre-main sequence
M67; red giant
Why does a star's life expectancy depend on mass? Mass determines the amount of fuel a star has for fusion. More massive stars can fuse hydrogen for a longer time. Mass determines the rate of fuel consumption for a star. Mass determines the amount of fuel a star has for fusion and more massive stars can fuse hydrogen for a longer time. Mass determines the amount of fuel a star has for fusion and determines the rate of fuel consumption for a star.
Mass determines the amount of fuel a star has for fusion and determines the rate of fuel consumption for a star.
Which is true for main-sequence stars? Massive stars are bright. Low-mass stars are bright. Massive stars are dim. None of these are true.
Massive stars are bright.
What happens to a star when it becomes a giant if it has a close binary companion? Radiation from the giant's surface can ionize the companion's gases. Radiation from the companion's surface can vaporize the giant. The giant can explode as a nova or supernova. Matter can be transferred from the companion to the giant. Matter can be transferred from the giant to the companion.
Matter can be transferred from the giant to the companion.
Consider the three H-R diagrams of the star clusters shown above: NGC2264, Pleiades, and M67. The youngest cluster is ________ and has ________ -type stars. M67; pre-main sequence NGC4622; pre-main sequence Pleiades; pre-main sequence M67; red giant
NGC4622; pre-main sequence
Which is a type of star found on the upper end of the main sequence? white dwarf O or B red supergiant red dwarf
O or B
Why is there an upper mass limit for main-sequence stars of about 100 solar masses? General relativity does not allow such massive objects to exist. Objects above this mass do form in molecular clouds; however, they emit no light and are not considered stars. Objects above this mass fuse hydrogen too rapidly and cannot stay together. The rotation rate is so high that such an object splits into a pair of stars. Giant molecular clouds do not contain enough material.
Objects above this mass fuse hydrogen too rapidly and cannot stay together.
Why is there a lower mass limit of 0.08 solar masses for main-sequence stars? Objects below this mass can only form in HI clouds. This is an unsolved astronomical mystery. They form too slowly and hot stars nearby clear the gas and dust quickly. Objects below this mass are not hot enough to fuse normal hydrogen. Our telescopes do not have enough light-gathering power to detect dim objects.
Objects below this mass are not hot enough to fuse normal hydrogen.
Why have no black dwarfs yet been observed in our galaxy? They are all too distant (in theory) to be detected. They can only be detected by their gravitational influence on a binary companion. Astronomers are not motivated to search for such objects. They are too dim for our present-day telescopes to detect. Our galaxy is too young for any to have formed.
Our galaxy is too young for any to have formed.
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. Theses stars have at least two active layers of fusion. These stars are fusing hydrogen at their surface. We cannot see the interior stars that are below this temperature as they are too dim. These stars have multiple concentric layers of active fusion.
Planetary nebulae glow due to the ionization of low density gas by a hot interior star.
Why does the surface temperature of an expanding star change? Since the star is getting bigger, it gets brighter and therefore hotter. Since there is more surface, more energy comes from the core and the star gets hotter. Since energy on the star's surface is spread out over more area, it gets cooler. None of these choices are correct.
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 energy on the star's surface is spread out over more area, it gets dimmer. Since the star is getting bigger, it has more area through which to give off energy, so it gets brighter. Since there is more surface, more energy comes from the core, so the star gets hotter and therefore brighter. None of these choices are correct.
Since the star is getting bigger, it has more area through which to give off energy, so it gets brighter.
What evidence do we have that some close binary pairs have merged to become a single giant star? Some giants are pulsating variable stars. Some giants are between luminosity classes. Some giant stars have rapid rotation. Alternating radial motion of a giant is revealed by an alternating Doppler shift. Two sets of spectral lines, one from each star, have been observed for some giants.
Some giant stars have rapid rotation.
Why will a helium flash never occur in some stars? Some stars do not develop degenerate helium cores. Some stars will never leave the main sequence. Some stars have a hydrogen flash in place of a helium flash. Some stars contain no helium. All of these choices are correct.
Some stars do not develop degenerate helium cores.
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. Stars spend about 30% of their fusion lifetimes on the main sequence. Stars spend about 50% of their fusion lifetimes on the main sequence. Stars spend about 10% of their fusion lifetimes on the main sequence. Stars spend about 70% of their fusion lifetimes on the main sequence.
Stars spend about 90% of their fusion lifetimes on the main sequence.
Which of the following statements accurately describe(s) some observed properties of supernovae type Ia and supernovae type II? Supernovae type Ia have hydrogen lines in their spectra. Supernovae type Ia are more luminous. Supernovae type Ia have hydrogen lines in their spectra and supernovae type Ia are more luminous. Supernovae type II have hydrogen lines in their spectra and supernovae type Ia are more luminous. Supernovae type II have hydrogen lines in their spectra.
Supernovae type II have hydrogen lines in their spectra and supernovae type Ia are more luminous.
How do star clusters confirm that stars are evolving? The H-R diagram of a star cluster is missing the lower part of the main sequence. The relative motion of stars in a cluster can be estimated by their Doppler shifts. The H-R diagram of a star cluster is missing the upper part of the main sequence. Star clusters occasionally lose members. Pulsating variable stars in globular clusters display a period-luminosity relationship.
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 lower the turnoff point, the older the star cluster. The lower the turnoff point, the older the star cluster. The higher the turnoff point, the older the star cluster. The age of a cluster is the life expectancy of stars at its turnoff point. 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.
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.
Why is there a mass-luminosity relationship? The temperature of a main-sequence star depends on the rate of fusion in the core, which depends on the mass. The brightness of a main-sequence star depends on the rate of fusion in the core, which depends on the temperature. The brightness of a main-sequence star depends on the rate of fusion in the core, which depends on the mass. All of these choices are correct.
The brightness of a main-sequence star depends on the rate of fusion in the core, which depends on the mass.
Which is a way that some stars avoid the helium flash? The core doesn't get hot enough for helium fusion. They aren't massive enough for helium fusion to begin in the core before it becomes degenerate. They are so massive that helium fusion cannot occur. All of these are ways that stars avoid the helium flash.
The core doesn't get hot enough for helium fusion.
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. They both increase. They both decrease. The luminosity decreases and the surface temperature increases. The luminosity and surface temperature are unchanged.
The luminosity increases and the surface temperature decreases.
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 moving toward Earth. The star is moving away from Earth. The star is not a Cepheid Variable. The star is slowly contracting. The star is slowly expanding.
The star is slowly expanding.
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 become a main-sequence star once again. The white dwarf can accrete too much matter and detonate as a supernova type Ia. 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. The white dwarf can become a main-sequence star once again and ignite the new matter and flare up as a nova. The white dwarf can ignite the new matter and flare up as a nova.
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.
Why can't the lowest-mass stars become giants? They never get hot enough for the triple-alpha process. Their gravity is too weak to stop them from expanding beyond the giant phase. They live so long that none has ever left the main sequence. They are fully convective and never develop a hydrogen shell fusion zone. The rate of hydrogen shell fusion is too slow to cause the star to expand.
They are fully convective and never develop a hydrogen shell fusion zone.
Which is true for the mass and life-expectancy of a star? They are inversely proportional: more massive stars burn hotter and brighter, and use up their hydrogen fuel faster. They are not the only interrelated factors: temperature must be considered too. They are proportional: more mass = longer life. They are not related.
They are not the only interrelated factors: temperature must be considered too.
Which is true of giant stars? They are of medium density. They are very dense. There is no generalization. They are of very low density.
They are of very low density.
What unusual property do all higher-mass white dwarfs have? They are smaller than lower-mass white dwarfs. They are cooler than lower-mass white dwarfs. They are less dense than lower-mass white dwarfs. They are less luminous than lower-mass white dwarfs. All of these choices are correct.
They are smaller than lower-mass white dwarfs.
What is the reason for giant stars having the densities that they do? They are so large. They are so hot. They are so bright. All of these choices are reasons.
They are so large.
Which is true for more massive main-sequence stars? They live a similar time to low-mass stars. They may live longer or shorter lives than low-mass stars, depending on their temperature. They live longer lives than low-mass stars. They live shorter lives than low-mass stars.
They live shorter lives than low-mass stars.
Why are lower-mass stars unable to ignite more massive nuclear fuels such as carbon? They never get hot enough. They did not accumulate enough carbon when they formed. They never get hot enough and carbon has too many neutrons in its nucleus. Carbon has too many neutrons in its nucleus. Beryllium is highly unstable.
They never get hot enough.
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 300 grams per cubic centimeter about 3,000,000 grams per cubic centimeter about 3 grams per cubic centimeter need more information to answer about 3,000 grams per cubic centimeter
about 3,000,000 grams per cubic centimeter
How much longer will the sun last? about 10 billion years about 10 million years It can't be predicted. about 5 billion years about 5 million years
about 5 billion years
What type of spectrum does the gas in a planetary nebula produce? an emission line spectrum a continuous spectrum an absorption line spectrum an emission line spectrum superimposed on a continuous spectrum All of these choices are correct.
an emission line spectrum
How can you estimate the age of a star cluster? by the number of stars by its coolest stars by the shape of the star cluster by its brightest stars
by its brightest stars
How do star clusters confirm that stars evolve? by the dimmer stars becoming brighter by the lack of less massive, cooler stars that die first by the more massive, brighter stars leaving the main sequence None of these choices are correct.
by the more massive, brighter stars leaving the main sequence
What prevents gravity from shrinking a white dwarf to a smaller size? hydrogen-shell fusion degenerate electrons hydrogen-core fusion helium-core fusion helium-shell fusion
degenerate electrons
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 getting smaller; evolves over getting smaller; stays the same with getting larger; stays the same with
getting larger; evolves over
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 open The average distances are about equal.
globular
What increases the temperature of an inert helium core inside a giant star? hydrogen shell fusion the triple-alpha process gravitational contraction hydrogen and helium shell fusion helium shell fusion
gravitational contraction
Which type of star eventually develops several concentric zones of active shell fusion? high-mass stars neutron stars white dwarfs medium-mass stars low-mass stars
high-mass stars
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? distance age diameter luminosity surface temperature
luminosity
Which of the following is NOT considered in making a simple stellar model? energy transport conservation of energy magnetic field hydrostatic equilibrium conservation of mass
magnetic field
Which is a type of star found on the lower end of the main sequence? white dwarf red giant O or B red dwarf
red dwarf
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 temperature decreases mass of individual nuclei increases fusion lifetime decreases All of these choices are correct.
temperature decreases and mass of individual nuclei increases
What event marks the end of every star's main-sequence life? the beginning of the CNO cycle the formation of a planetary nebula the end of hydrogen fusion in the core and beginning of the triple-alpha process the end of hydrogen fusion in the core the beginning of the triple-alpha process
the end of hydrogen fusion in the core
What is the helium flash? the explosion that destroys a star the beginning of helium fusion in the core of a star the explosion of the core of a star at the beginning of helium fusion All of these choices are correct.
the explosion of the core of a star at the beginning of helium fusion
What is the turnoff point of a star cluster? the point on the H-R diagram that stars in the cluster stop shining the location on the H-R diagram where stars are leaving the main sequence the time when the first stars in a cluster begin to die the time when the last stars in a cluster begin to die
the location on the H-R diagram where stars are leaving the main sequence
Which "variable" in variable stars confirms that stars evolve? its size the period of changes in brightness its brightness All of these choices are correct.
the period of changes in brightness
What happens to white dwarfs as they age? their surface temperatures decrease and luminosity decreases their surface temperatures decrease their luminosity decreases their size decreases All of these choices are correct.
their surface temperatures decrease and luminosity decreases
