Which of the following stars are brightest at ultraviolet wavelengths?
answer
O and B stars
question
What is the approximate surface temperature of a B star?
answer
20,000 K
question
The choices below each describe the appearance of an H-R diagram for a different star cluster. Which cluster
is the youngest?
answer
The diagram shows main-sequence stars of every spectral type except O, along with a few giants and
supergiants.
question
On a Hertzsprung-Russell diagram, where would you find stars that are cool and luminous?
answer
upper right
question
Which of the following statements about globular clusters is true?
answer
Most stars in the cluster are yellow or reddish in color.
question
A star's luminosity depends primarily on its
answer
radius and surface temperature.
question
What is the common trait of all main-sequence stars?
answer
They generate energy through hydrogen fusion in their core.
question
Star A is identical to Star B, except that Star A is twice as far from us as Star B. Therefore, ________.
answer
both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A
question
What is the approximate chemical composition (by mass) with which all stars are born?
answer
Three quarters hydrogen, one quarter helium, no more than 2% heavier elements
question
The sketch above shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents
the entire main sequence while (c) and (d) represent only small parts of the main sequence. Which group
represents stars with the longest main-sequence lifetimes?
answer
d .
question
Which of the following terms is given to a pair of stars that appear to change position in the sky, indicating
that they are orbiting one another?
answer
visual binary
question
Which of the following statements about spectral types of stars is true?
answer
All of the above are true.
question
What is the spectral type of the star with the strongest hydrogen absorption lines?
answer
A
question
Which stellar spectral type has strong molecular absorption lines in its optical spectrum?
answer
B
question
On a Hertzsprung-Russell diagram, where would you find stars that are cool and have low luminosities?
answer
lower right
question
Which of the following statements about apparent and absolute magnitudes is true?
answer
All of the above are true.
question
What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us?
answer
It is the spectral type of the hottest main-sequence star in a star cluster, and it tells us the cluster's age
question
On an H-R diagram, stellar masses ________.
answer
can be determined for main-sequence stars but not for other types of stars
question
A star of spectral type B with a mass of 10 times the mass of the Sun will last approximately how long on the
main sequence?
answer
10 million years
question
Besides mass, what else can be determined about the stars in an eclipsing binary system by observing their
light curve?
answer
their radii
question
How is the lifetime of a star related to its mass?
answer
.
More massive stars live much shorter lives than less massive stars.
question
On a Hertzsprung-Russell diagram, where would you find white dwarfs?
answer
lower left
question
The sketch above shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents
the entire main sequence while (c) and (d) represent only small parts of the main sequence. Which group
represents the most common type of stars?
answer
d
question
it is a graph with a blocked question:-)
answer
A) About 1 solar
question
The total amount of power (in watts, for example) that a star radiates into space is called its ________.
answer
luminosity
question
The sketch above shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents
the entire main sequence while (c) and (d) represent only small parts of the main sequence. Which group
represents stars that have no ongoing nuclear fusion?
answer
b
question
Why do disks form around young stars?
answer
Collisions between rotating gas particles flatten the gas cloud along its axis of rotation.
question
Approximately what core temperature is required before hydrogen fusion can begin in a star?
answer
10 million K
question
Which star spends the longest time in the protostellar phase of life?
answer
a 1 solar mass star
question
What is the CNO cycle?
answer
a type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts
question
What types of stars end their lives with supernovae?
answer
stars that are more massive than eight times the mass of the Sun
question
Why does a star grow larger immediately after it exhausts its core hydrogen?
answer
Hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper
layers outward.
question
If the Sun somehow acquired more hydrogen and helium and doubled in mass, what would happen to it?
answer
It would evolve more quickly than it is now.
question
How are elements beyond iron formed in massive-star supernovae?
answer
Neutrons produced during the core collapse are slammed into atomic nuclei.
question
This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman
numerals. Which stage lasts the longest?
answer
iii
question
What is a planetary nebula?
answer
gas ejected from a star in the final stage of its life
question
Which of the following statements about brown dwarfs is not true?
answer
Brown dwarfs eventually collapse to become white dwarfs.
question
Where would a brown dwarf be located on an H-R diagram?
answer
below and to the right of the lowest part of the main sequence
question
What can we learn about a star from its life track on an H-R diagram?
answer
what surface temperature and luminosity it will have at each stage of its life
question
The main source of energy for a star as it grows in size to become a red giant is ________.
answer
hydrogen fusion in a shell surrounding the central core
question
Which of the following statements about degeneracy pressure is not true?
answer
Degeneracy pressure varies with the temperature of the star.
question
When does a star become a main-sequence star?
answer
when the rate of hydrogen fusion in the star's core is high enough to sustain gravitational equilibrium
question
You observe a red giant star. What is happening to that star?
answer
It is increasing in size, and is fusing hydrogen in a shell around its core.
question
Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion
or fission?
answer
iron
question
Based on current understanding, the minimum mass of a black hole that forms during a massive star
supernova is roughly ________.
answer
3 solar masses
question
Which statement about accretion disks is not true?
answer
The primary factor determining whether a white dwarf has an accretion disk is the white dwarf's mass.
question
What kind of star is most likely to become a white-dwarf supernova?
answer
a white dwarf star with a red giant binary companion
question
Suppose you were unfortunate enough to fall into a black hole in a binary system where the black hole was
accreting matter from its companion star. Which of the following is most likely to kill you first?
answer
X-rays from the accretion disk
question
Which of the statements below about black holes is not true?
answer
A spaceship passing a few million kilometers from a 10 solar mass black hole is much more likely to be
destroyed than a spaceship passing at the same distance from the center of a 10 solar mass
main-sequence star
question
If you were to come back to our solar system in 6 billion years, what might you expect to find?
answer
a white dwarf
question
Based on current evidence, which of the following statements about gamma-ray bursts is true?
answer
All the bursts that we have detected occurred in distant galaxies.
question
According to our modern understanding, what is a nova?
answer
an explosion on the surface of a white dwarf in a close binary system
question
Will our Sun ever undergo a white dwarf supernova explosion? Why or why not?
answer
No, because it is not orbited by another star.
question
Which of the following hypothetical observations would contradict our theories about the formation and
evolution of white dwarfs?
answer
discovery of a white dwarf with a mass 1.5 times that of the Sun (1.5 Msun)
question
After a massive-star supernova, what is left behind?
answer
either a neutron star or a black hole
question
Which of the following best describes what would happen if a 1.5 solar mass neutron star, with a diameter of
a few kilometers, were suddenly to appear in your hometown?
answer
The entire mass of the Earth would end up as a thin layer, about 1 cm thick, over the surface of the
neutron star.
question
Which of the following stellar properties has the greatest range in values?
answer
luminosity
question
A star is observed with a surface t
answer
0.1 solar radius
question
On the main sequence, stars obtain their energy
answer
by converting hydrogen to helium.
question
The choices below each describe the appearance of an H-R diagram for a different star cluster. Which cluster
is most likely to be located in the halo of our galaxy?
answer
The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants
and white dwarfs.
question
What is the approximate luminosity of a main-sequence M star?
answer
0.01 solar
question
Why do O stars exhibit weak hydrogen absorption lines?
answer
At these high temperatures, nearly all the hydrogen is ionized, and is therefore unable to interact with
light.
question
Careful measurements reveal that a star maintains a steady apparent brightness at most times, except that at
precise intervals of 73 hours the star becomes dimmer for about 2 hours. The change in brightness alternates
between a small change and a large change. The most likely explanation is that ________.
answer
the star is a member of an eclipsing binary star system
question
A star of spectral type G will last approximately how long on the main sequence?
answer
10 billion years
question
What happens after the helium flash in the core of a star?
answer
The core quickly heats up and expands as helium fusion begins all at once throughout the core.
question
Why does stellar main-sequence lifetime decrease with increasing stellar mass?
answer
Higher core temperatures cause fusion to proceed much more rapidly.
question
Consider the star to which the arrow points. Which of the following statements about this star is not true?
answer
It is significantly less massive than the Sun.
question
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?
answer
Near the end of a high-mass star's life, it produces new elements through a series of helium capture
reactions.
question
Which of the following types of stars is the most common?
answer
M stars
question
If you had something the size of a sugar cube that was made of white dwarf matter, on Earth it would weigh
________.
answer
as much as a large vehicle
question
What do we mean by the singularity of a black hole?
answer
It is the center of the black hole, a place of infinite density where the known laws of physics cannot
describe the conditions.
question
Suppose a white dwarf is gaining mass because of accretion from a binary companion. What happens if its
mass reaches the 1.4 solar mass limit?
answer
Temperatures skyrocket to the point where carbon fusion is possible, which leads to a white dwarf
supernova explosion.
question
Which of the following correctly states the relationship between the apparent brightness, luminosity, and distance of a star?
answer
apparent brightness = luminosity/ 4pi x (distance)^2
question
The spectral sequence sorts stars according to
answer
surface temperature.
question
Which of the following types of data provide evidence that helps us understand the post main-sequence life
tracks of low-mass stars?
answer
H-R diagrams of globular clusters
question
Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you
expect to be true?
answer
A few massive stars will form, live, and die before the majority of the star's clusters even complete their
protostar stage.
question
A white dwarf is ________.
answer
what most stars become when they die
question
A main-sequence star's luminosity can directly inform us of
answer
the rate at which it converts hydrogen to helium.
question
What is the CNO cycle?
answer
a set of steps by which four hydrogen nuclei fuse into one helium nucleus
question
When we see X-rays from an accretion disk in a binary system, we can't immediately tell whether the
accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following
phenomena in this system. Which one would rule out the possibility of a black hole?
answer
intense X-ray bursts
question
Two stars have the same spectral type. Star X is in luminosity class III, while Star Y is in luminosity class V.
Star X must be larger in radius than Star Y.
answer
True
question
A 10 solar mass star is about ten times more luminous than a 1 solar mass star.
answer
False
question
The apparent brightness of a star depends only on its luminosity.
answer
False
question
The more distant a star, the smaller its parallax.
answer
True
question
Two stars both lie on the main sequence. Star X is spectral type A, while Star Y is spectral type G. Star X must
be more massive than Star Y.
answer
True
question
We can measure the parallax of most stars in our galaxy.
answer
False
question
Our Sun will end its life in a planetary nebula and become a white dwarf.
answer
True
question
Stars with high masses live longer than stars with lower masses.
answer
False
question
The heaviest element produced by stars or in supernovae is silicon.
answer
False
question
The helium fusion process works by fusing two helium nuclei into one beryllium nucleus.
answer
False
question
More massive white dwarfs are smaller than less massive white dwarfs.
answer
True
question
Our Sun will likely undergo a nova event in about 5 billion years.
answer
False
question
All massive-star supernovae leave behind black holes as remnants.
answer
False
question
White dwarfs are all about the same size
answer
True
question
The faintest stars visible to the naked eye have an apparent magnitude of about 6.
answer
True
question
Photographs of many young stars show long jets of material apparently being ejected from their poles.
answer
True
question
Light escaping from white dwarfs will show a gravitational redshift.
answer
True
question
Some stars are cool enough to have molecules in their atmosphere.
answer
True
question
In any star cluster, stars with lower masses greatly outnumber those with higher masses.
answer
True
question
The maximum mass for a white dwarf is 1.4 solar masses.
answer
True
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