Astronomy ch. 16 - Mastering Astronomy
Provided following are the spectral types of four different main-sequence stars. Rank the stars based on the strength of the radiation pressure that pushes outward as they are forming, from highest pressure to lowest pressure. 1. O9 (Dark blue) 2. M6 (red) 3.G2 (yellow) 4.A5 (light blue)
1. O9 (Dark blue) 4.A5 (light blue) 3.G2 (yellow) 2. M6 (red)
Provided following are four different ranges of stellar masses. Rank the stellar mass ranges based on how many stars in each range you would expect to be born in a star cluster, from highest number to lowest number. 1. between 1 and 10 solar masses 2.between 30 and 60 solar masses 3.less than 1 solar mass 4. between 10 and 30 solar masses
3.less than 1 solar mass 1. between 1 and 10 solar masses 4. between 10 and 30 solar masses 2.between 30 and 60 solar masses
What percentage of a molecular cloud's mass is interstellar dust? A. 1% B. 1-50%, depending on the mass of the molecular cloud C. 50% D. 28% E.2%
A. 1%
For every star with a mass greater than 10 solar masses, about how many stars are there with masses less than a solar mass? A. 200 B. 1 C. 30 D. 3 E. 10
A. 200
What is the smallest mass a newborn star can have? A. 80 times the mass of Jupiter B. 800 times the mass of Jupiter C. about 1/800 the mass of our Sun D. 8 times the mass of Jupiter E. about 1/80 the mass of our Sun
A. 80 times the mass of Jupiter
The life tracks shown on the diagram for different mass protostars are based on computer models. Observationally, how can astronomers test whether these models are correct? View Available Hint(s) A. By observing and comparing protostars and stars of different masses within a single star cluster. B. By observing and comparing protostars and stars of different masses at different distances from the center of the Milky Way Galaxy. C. By monitoring protostars of different mass over many years and comparing the changes during those years to the predictions of the computer models.
A. By observing and comparing protostars and stars of different masses within a single star cluster.
The most abundant molecule in molecular clouds is A. H2. B. H2O. C. CO. D. He2. E. HHe.
A. H2.
Suppose two protostars form at the same time, one with a mass of 0.5MSun and the other with a mass of 15MSun. Which of the following statements are true? A. The 15MSun protostar will be much more luminous than the 0.5MSun protostar. B. The 15MSun star will end its main-sequence life before the 0.5MSun star even completes its protostar stage. C. The 15MSun protostar will orbit the Milky Way Galaxy at much higher speed than the 0.5MSun protostar.
A. The 15MSun protostar will be much more luminous than the 0.5MSun protostar. B. The 15MSun star will end its main-sequence life before the 0.5MSun star even completes its protostar stage.
Based on the protostar tracks on the diagram, which statement must be true about the Sun? A. The Sun was much more luminous when it was a protostar than it is today. B. The Sun was much hotter when it was a protostar than it is today. C. The Sun is 30 million years old. D. The Sun was cooler and dimmer when it was a protostar than it is today.
A. The Sun was much more luminous when it was a protostar than it is today.
The thermal pressure of a gas depends on A. density and temperature. B. gravity. C. composition. D. density only. E. temperature only.
A. density and temperature.
When does a protostar become a true star? A. when nuclear fusion begins in the core B. when the central temperature reaches 1 million Kelvin C. when the stellar winds and jets blow away the surrounding material D. when the thermal energy becomes trapped in the center E. when the star is 1 million years old
A. when nuclear fusion begins in the core
The typical size of an interstellar dust grain is The typical size of an interstellar dust grain is A. 1 centimeter. B. 1 micrometer. C. 1 millimeter. D. 1 angstrom. E. 1 nanometer.
B. 1 micrometer.
Although some photographs show what looks like jets of material near many young stars, we now know that these "jets" actually represent gas from the surrounding nebula that is falling onto the stars. A. TRUE B. FALSE
B. FALSE
Watch the red dot representing the protostar in the video. After it reaches its highest point on the diagram, how do the protostar's surface temperature and luminosity change as it approaches the main sequence? A. Its surface temperature decreases, but its luminosity increases. B. Its surface temperature increases, but its luminosity decreases. C. Its surface temperature and luminosity both decrease. D. Its surface temperature and luminosity both increase.
B. Its surface temperature increases, but its luminosity decreases.
Based on observations (both images and spectra), which of the following statements are true about star-forming clouds? A. Star-forming clouds are much hotter than most other interstellar material in the galaxy. B. Star-forming clouds have the same overall chemical composition as the galaxy as a whole. C. Most of the hydrogen in star-forming clouds is in the form of hydrogen molecules (H2). D. The darkness of these clouds (in visible light) is due primarily to light absorption by tiny grains of interstellar dust. E. The densest cloud regions appear dark to visible light telescopes but we can see into these regions with Infrared telescopes. F. Young stars shine only in the infrared, which is why infrared observations are important. G. Star-forming clouds glow with visible light in regions where the gas is heated by radiation from nearby stars.
B. Star-forming clouds have the same overall chemical composition as the galaxy as a whole. C. Most of the hydrogen in star-forming clouds is in the form of hydrogen molecules (H2). D. The darkness of these clouds (in visible light) is due primarily to light absorption by tiny grains of interstellar dust. E. The densest cloud regions appear dark to visible light telescopes but we can see into these regions with Infrared telescopes. G. Star-forming clouds glow with visible light in regions where the gas is heated by radiation from nearby stars.
Which of the following represents key observational evidence that stars are born in clouds of gas and dust? A. Younger star clusters have hotter and bluer stars than older star clusters. B. Young star clusters are always associated with clouds of gas and dust. C.Younger star clusters have main-sequence turnoff points that are higher up on the H-R diagram. D. Old globular clusters are shaped somewhat like giant clouds.
B. Young star clusters are always associated with clouds of gas and dust.
As a clump of interstellar gas contracts to become a main-sequence star, its changing position on the H-R diagram tells us __________. A. the time during which it existed in the history of the universe B. how its outward appearance is changing C. how it moves through the galaxy
B. how its outward appearance is changing
The five colored curves on the diagram have arrows pointing to the left. Each of these five curves represents a star of a different __________. A. surface temperature B. mass C. distance from Earth D. age
B. mass
The arrows on each protostar's curve on the diagram's indicate that __________. A. protostars move through space and come to rest only when they become main-sequence stars B. protostars change in surface temperature and luminosity as they develop C. protostars change in mass as they age
B. protostars change in surface temperature and luminosity as they develop
Which protostars maintain nearly the same luminosity throughout the time that they are protostars? A. protostars that eventually become main-sequence stars B. protostars with masses about 10 or more times that of the Sun C. red protostars D. protostars with masses about that of the Sun or less
B. protostars with masses about 10 or more times that of the Sun
What is the greatest mass a newborn star can have A. 20 solar masses. B. 10 solar masses. C. a few hundred solar masses. D. 50 solar masses.
C. a few hundred solar masses.
Suppose a new star cluster is born with one O star, 10 A stars, 100 G stars, and 1000 M stars. Which stellar type dominates the light output from the cluster? A. class M B. class G C. class O D. class A
C. class O
Calculations show that gravity begins to overcome thermal pressure in clouds that are A. more massive than a thousand times the Sun. B. less massive than the Sun. C. more massive than a hundred times the Sun. D. more massive than ten times the Sun. E. more massive than the Sun.
C. more massive than a hundred times the Sun.
Why does it make sense for star-forming clouds to be cold and dense? A. these conditions allow the cloud to glow in the infrared B. young stars need cold and dense gas to absorb their heat C. these conditions help gravity overcome gas pressure D. these conditions create more contrast with hot stars
C. these conditions help gravity overcome gas pressure
What would the color of this star cluster appear to be if you observed it from a distance so great that you could not make out the individual stars? A. green B. red C. violet D. blue
C. violet
When does a newly forming star have the greatest luminosity? A. when its surface temperature is the highest B. when it first becomes a main-sequence star C. when it is a shrinking protostar with no internal fusion D. when its internal temperature becomes high enough for nuclear fusion
C. when it is a shrinking protostar with no internal fusion
Which of the following best explains the current state of agreement between theoretical models of star formation and observations of star formation? A. Scientists have not yet developed models that can explain why stars are born in molecular clouds. B. Current models can explain all aspects of star birth except why stars are made mostly of hydrogen and helium. C. Current models provide an essentially perfect match to what we observe in star-forming clouds. D. Current models can reproduce general features of star birth, but not all the details.
D. Current models can reproduce general features of star birth, but not all the details.
What is the eventual fate of a brown dwarf? A. Gravity ultimately "wins" and it becomes a small black hole. B. It remains the same forever. C. It becomes ever denser and hotter until it becomes a white dwarf. D. It gradually cools down and becomes ever dimmer. E. It gradually contracts and heats up until nuclear fusion ignites in its interior and it becomes a faint star.
D. It gradually cools down and becomes ever dimmer.
What happens to the surface temperature and luminosity when gravity first assembles a protostar from a collapsing cloud? A. Its surface temperature and luminosity remain the same. B. Its surface temperature remains the same and its luminosity decreases. C. Its surface temperature and luminosity decrease. D. Its surface temperature and luminosity increase. E. Its surface temperature decreases and its luminosity increases.
D. Its surface temperature and luminosity increase.
What prevents the pressure from increasing as a cloud contracts due to its gravity? A. Once the cloud reaches a critical density, the pressure becomes degenerate and independent of temperature. B. The pressure is transferred from the center of the cloud to its outer edges where it can dissipate. C. As the cloud becomes denser, gravity becomes stronger and overcomes the pressure buildup. D. Thermal energy is converted to radiative energy via molecular collisions and released as photons. E. Excess pressure is released in jets of material from the young stars.
D. Thermal energy is converted to radiative energy via molecular collisions and released as photons.
Which of the following discoveries, if they existed, would necessitate a reevaluation of our ideas of stellar formation? A. planetary systems around other stars than our own B. a 100-solar-mass star C. a cluster of stars that appeared to be 13 billion years old D. a 0.01-solar-mass star E. a molecular cloud without any stars
D. a 0.01-solar-mass star
The dark area stretching from the center of this picture to the upper right is about 50 light-years long and lies in the plane of the Milky Way Galaxy. What is it? The figure shows an image of starry sky with an oblong area with much lesser star density in it, compared to the surrounding space. A. a region of the galactic plane in which there are few stars B. the expanding remains of a supernova C. a black hole D. a star-forming cloud
D. a star-forming cloud
What law explains why a collapsing cloud usually forms a protostellar disk around a protostar? A. the universal law of gravitation B. Wien's law C. Kepler's third law D. conservation of angular momentum
D. conservation of angular momentum
When a newly forming star is at its greatest luminosity, what is its energy source? A. nuclear fusion of hydrogen into helium B. A newly forming star has no energy source because it does not shine at all until it becomes a true main-sequence star. C. radioactive decay of unstable isotopes D. gravitational contraction
D. gravitational contraction
If you wanted to observe stars behind a molecular cloud, in what wavelength of light would you most likely observe? A. visible B. gamma-ray C. X-ray D. infrared E. ultraviolet
D. infrared
About how many times more luminous than our Sun is a young solar mass protostar just beginning convective contraction? A. 5-10 B. 100-1000 C. a million D. 2-5 E. 10-100
E. 10-100
No stars have been found with masses greater than 300 times our Sun because A. they shine exclusively at X-ray wavelengths and become difficult to detect. B. they are not bright enough to be seen nearby. C. molecular clouds do not have enough material to form such massive stars. D. they would fragment into binary stars because of their rapid rotation. E. they would generate so much power that they would blow themselves apart.
E. they would generate so much power that they would blow themselves apart.
When does a star become a main-sequence star? A. the instant when hydrogen fusion first begins in the star's core B. when a star becomes luminous enough to emit thermal radiation C. when the protostar assembles from a molecular cloud D. when hydrogen fusion is occurring throughout a star's interior E. when the rate of hydrogen fusion within the star's core is high enough to maintain gravitational equilibrium
E. when the rate of hydrogen fusion within the star's core is high enough to maintain gravitational equilibrium
The following figures show four stages that occur during the formation of a one-solar-mass star. Rank these stages based on their rotation rate, from fastest to slowest. (Assume that the angular momentum of the forming star is conserved throughout the formation process, though in fact it may shed some angular momentum by ejecting material into interstellar space.) 1. Molecular-cloud fragment, 2. Main-sequence star 3. contracting trapping infrared light 4. protostar with jets
FASTEST TO SLOWEST ROTATION 2. Main-sequence star 4. protostar with jets 3. contracting trapping infrared light 1. Molecular-cloud fragment,
Jupiter is a failed star. True or false?
False
The following figures show four stages that occur during the formation of a one-solar-mass star. Rank these stages based on the order in which they occur, from first to last. 1. Molecular-cloud fragment, 2. Main-sequence star 3. contracting trapping infrared light 4. protostar with jets
First to occur to Last to occur: 1. Molecular-cloud fragment, 3. contracting trapping infrared light 4. protostar with jets 2.main-sequence star
The following figures show four stages that occur during the formation of a one-solar-mass star. Rank these stages based on the central temperature, from highest to lowest. 1. Molecular-cloud fragment, 2. Main-sequence star 3. contracting trapping infrared light 4. protostar with jets
Highest to Lowest 2. Main-sequence star 4. protostar with jets 3. contracting trapping infrared light 1. Molecular-cloud fragment,
The following figures show the spectral types of four main-sequence stars. Rank them based on the time each takes, from longest to shortest, to go from a protostar to a main-sequence star during the formation process. 1. O9 (Dark blue) 2. M6 (red) 3.G2 (yellow) 4.A5 (light blue)
Longest to Shortest time: 2. M6 (red) 3.G2 (yellow) 4.A5 (light blue) 1. O9 (Dark blue)
Each item following is a characteristic of a one-solar-mass star either during its protostar phase or during its main-sequence phase. Match the items to the appropriate phase. 1.Pressure and gravity are not precisely balanced 2. lasts about 10 billion years 3. energy generated by gravitational contraction 4. luminosity much greater than the Sun 5. radius much larger than the Sun 6. surface radiates energy at same rate that core generates energy 7. energy generated by nuclear fusion
Protostar : 5. radius much larger than the Sun 1. Pressure and gravity are not precisely balanced 4. luminosity much greater than the Sun 3. energy generated by gravitational contraction Main-sequence phase : 6. surface radiates energy at same rate that core generates energy 7. energy generated by nuclear fusion 2. lasts about 10 billion years
