321 notecards = 81 pages (4 cards per page)
1) What is the diameter of the disk of the Milky Way?
2) What is the thickness of the disk of the Milky Way?
3) What kinds of objects lie in the halo of our galaxy?
4) What kinds of objects lie in the disk of our galaxy?
5) Which of the following comprise the oldest members of the Milky
6) What makes up the interstellar medium?
7) If you were to take a voyage across the Milky Way, what kind of
material would you spend most of your time in?
8) How does the interstellar medium obscure our view of most of the
9) How can we see through the interstellar medium?
10) Harlow Shapley concluded that the Sun was not in the center of
the Milky Way Galaxy by
11) Approximately how far is the Sun from the center of the galaxy?
12) What do astronomers consider heavy elements?
13) Where are most heavy elements made?
14) Why are we unlikely to find Earth-like planets around halo stars
in the Galaxy?
15) How are interstellar bubbles made?
16) What is a superbubble?
17) Sound waves in space
18) What is a shock front?
20) What can cause a galactic fountain?
21) What is the galactic fountain model?
22) What evidence supports the galactic fountain model?
23) What is the most common form of gas in the interstellar medium?
24) What produces the 21-cm line that we use to map out the Milky Way
25) Where do most dust grains form?
26) Suppose you read somewhere that 10 percent of the matter in the
Milky Way is in the form of dust grains. Should you be surprised? If
27) The image of our galaxy in radio emission from CO, mapping the
distribution of molecular clouds, is closest to the image of our
28) Compared with our Sun, most stars in the halo are
29) Compared with stars in the disk, orbits of stars in the halo
30) Approximately how long does it take the Sun to orbit the Milky
31) Where does most star formation occur in the Milky Way today?
32) How do we know that spheroidal stars are older, on average, than
33) Which of the following statements about globular clusters is
34) Which of the following statements about the disk of the Milky Way
35) Which of the following statements about halo stars is false?
36) What evidence suggests that the protogalactic cloud that formed
the Milky Way resulted from several collisions among smaller clouds?
37) Which constellation lies in the direction toward the galactic
38) How do we learn about what is going on in the center of our own
galaxy (the Milky Way)?
39) Which of the following does not accurately describe what we
observe toward the Galactic center?
40) What evidence supports the theory that there is a black hole at
the center of our galaxy?
41) What is SgrA*?
42) What evidence do we have that the spheroidal population of stars
are older than other stars in the galaxy?
1) Open clusters and young stars are generally found only in the disk of the galaxy and not in the halo.
2) We can see most of the galaxy with visible light.
3) Observing the galaxy at radio wavelengths allows us to see beyond the dust in the disk of the galaxy that obscures our view.
4) The Milky Way looks the same in X rays as it does at infrared wavelengths.
5) The Sun is located at the edge of the galaxy, approximately 50,000 light-years from the galactic center.
6) Shapley used the distribution of globular clusters in the galaxy to determine that the Sun was not at the center of the Milky Way.
7) All heavy elements are made during supernova events.
8) The star-gas-star cycle will continue forever because stars are continually recycling gas.
9) Almost all elements heavier than hydrogen and helium were made inside stars.
10) Most of the current star formation in the Milky Way occurs in spiral arms.
1) How does the diameter of the disk of Milky Way Galaxy compare to
2) What do we call the bright, sphere-shaped region of stars that
occupies the central few thousand light-years of the Milky Way Galaxy?
3) The Sun's location in the Milky Way Galaxy is
4) What do we mean by the interstellar medium?
5) What are the Magellanic Clouds?
6) How do disk stars orbit the center of the galaxy?
7) How do we know the total mass of the Milky Way Galaxy that is
contained within the Sun's orbital path?
8) Elements heavier than hydrogen and helium constitute about
________ of the mass of the interstellar medium.
9) What do we mean by the star-gas-star cycle?
10) What are cosmic rays?
11) The primary way that we observe the atomic hydrogen that makes up
most of the interstellar gas in the Milky Way is with
12) Which of the following analogies best describes how the structure
of the galaxy's spiral arms is maintained?
13) What do we mean by a protogalactic cloud?
14) Most stars in the Milky Way's halo are
15) What is an ionization nebula?
16) What do halo stars do differently from disk stars?
17) Where does most star formation occur in the Milky Way Galaxy?
18) Based on observations, which of the following statements about
stars in the Milky Way is generally true?
19) What kind of object do we think lies in the center of the Milky
1) If we could see our own galaxy from 2 million light-years away, it
2) How does the interstellar medium affect our view of most of the
3) Applying the Newton's version of Kepler's third law (or the
orbital velocity law) to the a star orbiting 40,000 light-years from
the center of the Milky Way Galaxy allows us to determine
4) How would you expect a star that formed recently in the disk of
the galaxy to differ from one that formed early in the history of the
5) Suppose a scientist holds a press conference at which he claims
that 10% of the matter in the Milky Way is in the form of dust grains.
Does his claim seem reasonable? Why or why not?
6) The most common form of gas in the disk of the Milky Way Galaxy
7) How should we expect the Milky Way's interstellar medium to be
different in 50 billion years than it is today?
8) Over time, the star-gas-star cycle leads the gas in the Milky Way
9) Suppose you want to observe and study the radiation from gas
inside an interstellar bubble created by a supernova. Which of the
following observatories will be most useful?
10) If you could watch a time-lapse movie of the interstellar medium
over hundreds of millions of years, what would you see?
12) All the following types of objects are found almost exclusively
in the disk (rather than the halo) of the Milky Way except
13) Red and orange stars are found evenly spread throughout the
galactic disk, but blue stars are typically found
14) Which of the following statements comparing halo stars to our Sun
is not true?
15) Most nearby stars move relative to the Sun at speeds below about
30 km/s. Suppose you observe a nearby star that is moving much faster
than this (say, 300 km/s). Which of the following is a likely
explanation for its high speed?
16) Why do we believe that most of the mass of the Milky Way is in
the form of dark matter?
17) Spiral arms appear bright because
18) How did star formation likely proceed in the protogalactic cloud
that formed the Milky Way?
19) If we could watch spiral arms from a telescope situated above the
Milky Way over 500 million years, what would we see happen?
20) What is the best evidence for an extremely massive black hole in
the center of the Milky Way?
21) Which of the following statements is not true of the object known
as Sgr A* in the center of our Galaxy?
2) Suppose that we look at a photograph of many galaxies. Assuming
that all galaxies formed at about the same time, which galaxy in the
picture is the youngest?
3) Which of the following types of galaxies are most spherical in
4) Which of the following types of galaxies are reddest in color?
5) Which of the following statements about galaxies is true?
6) Which types of galaxies have a clearly defined spheroidal
7) Which types of galaxies have a clearly defined disk component?
8) Compared to spiral galaxies, elliptical galaxies are
9) The disk component of a spiral galaxy includes which of the
10) How does a lenticular galaxy differ from a normal spiral galaxy?
11) What is the major difference between an elliptical galaxy and a
12) Most large galaxies in the universe are
13) Which of the following types of galaxies are most commonly found
in large clusters?
14) Approximately how many stars does a dwarf elliptical galaxy have?
15) Which of the following is true about irregular galaxies?
16) Why are Cepheid variables important?
17) What is a standard candle?
18) Why is the Hyades Cluster important for building up a catalog of
the true luminosities of main-sequence stars?
20) How was Edwin Hubble able to use his discovery of a Cepheid in
Andromeda to prove that the "spiral nebulae" were actually
21) What two quantities did Edwin Hubble plot against each other to
discover the expansion of the Universe?
22) What is Hubble's law?
24) What is the primary practical difficulty that limits the use of
Hubble's law for measuring distances?
25) White-dwarf supernovae are good standard candles for distance
measurements for all the following reasons except which?
26) What makes white-dwarf supernovae good standard candles?
27) What is the most accurate way to determine the distance to a
28) What is the most accurate way to determine the distance to a
29) What is the most accurate way to determine the distance to a very
distant irregular galaxy?
30) Which of the following sequences lists the methods for
determining distance in the correct order from nearest to farthest?
31) Dr. X believes that the Hubble constant is H0 = 55 km/s/Mpc. Dr.
Y believes it is H0 = 80 km/s/Mpc. Which statement below automatically
32) Dr. Smith believes that the Hubble constant is H0 = 70 km/s/Mpc.
Dr. Jones believes it is H0 = 50 km/s/Mpc. Which statement below
33) Recall that Hubble's law is written v = H0d, where v is the
recession velocity of a galaxy located a distance d away from us, and
H0 is Hubble's constant. Suppose H0 = 65 km/s/Mpc. How fast would a
galaxy located 500 megaparsecs distant be receding from us?
34) Hubble's "constant" is constant in
35) Based on current estimates of the value of Hubble's constant, how
old is the universe?
37) What does the equivalent of an H-R diagram for galaxies, plotting
luminosity versus color, show?
1) Although it is difficult to tell from our vantage point inside the galaxy, astronomers suspect that the Milky Way is a barred spiral.
2) Spiral galaxies have more gas, dust, and younger stars than elliptical galaxies do.
3) Stars are continually forming in the halo of our Galaxy today.
4) A lenticular galaxy is another name for an elongated elliptical galaxy.
5) There are more large spiral galaxies than there are large elliptical galaxies.
6) Elliptical galaxies are more likely to be found in clusters than are spiral galaxies.
7) Massive-star supernovae and white-dwarf supernovae work equally well as standard candles for measuring cosmic distances.
8) The larger the value of Hubble's constant, the more rapid the expansion of the universe and hence the younger the universe.
1) Based on the number of galaxies visible in the Hubble Deep Field
(Figure 20.1 in your textbook), the estimated number of galaxies in
our observable universe is
2) Which of the following is not one of the three major categories of
3) Galaxies with disks but no evident spiral arms are called
4) Which of the following best describes the status of the Milky Way
in our Local Group of galaxies?
5) A standard candle is
6) What is main-sequence fitting?
7) What is a Cepheid variable?
8) What two observable properties of a Cepheid variable are directly
related to one another?
9) What does Hubble's law tell us?
10) Given that white dwarf supernovae are such good standard candles,
why don't we use them to measure the distance to all galaxies?
12) When we use an analogy that represents the expanding universe
with the surface of an expanding balloon, what does the inside of the
13) If we say that a galaxy has a lookback time of 1 billion years,
we mean that
14) Cosmological redshift is the result of
17) You observe the peak brightnesses of two white dwarf supernovae.
Supernova A is only 1/4 as bright as Supernova B. What can you say
about their relative distances?
18) The fact that the universe is expanding means that space itself
is growing within
19) Spectral lines from Galaxy B are redshifted from their rest
wavelengths twice as much as the spectral lines from Galaxy A/B.
According to Hubble's law, what can you say about their approximate
1) In a photo like the Hubble Deep Field (Figure 20.1 in your
textbook), we see galaxies in many different stages of their lives. In
general, which galaxies are seen in the earliest (youngest) stages of
2) Which of the following statements about types of galaxies is not
3) The most basic difference between elliptical galaxies and spiral
galaxies is that
4) Hubble's galaxy classification diagram (the "tuning
5) Using the technique of main-sequence fitting to determine the
distance to a star cluster requires that
6) Suppose that we suddenly discovered that all these years we'd been
wrong about the distance from Earth to the Sun, and it is actually 10%
greater than we'd thought. How would that affect our estimate of the
distance to the Andromeda Galaxy?
7) Suppose we observe a Cepheid variable in a distant galaxy. The
Cepheid brightens and dims with a regular period of about 10 days.
What can we learn from this observation?
9) Suppose that Hubble's constant were 20 kilometers per second per
million light-years. How fast would we expect a galaxy 100 million
light-years away to be moving? (Assume the motion is due only to
10) Does Hubble's law work well for galaxies in the Local Group? Why
or why not?
11) Why are white dwarf supernovae more useful than massive star
supernovae for measuring cosmic distances?
12) Suppose an elliptical galaxy is so far away that we cannot see
even its brightest stars individually. Which of the following
techniques might allow us to measure its distance?
13) What is the best way to determine a galaxy's redshift?
14) Which statement below correctly describes the relationship
between expansion rate and age for the universe?
15) What does cosmological redshift do to light?
16) The lookback time of the cosmological horizon is
17) Why can't we see past the cosmological horizon?
18) Hubble's constant is about 22 km/s/million light-years, implying
an age of about 14 billion years for the universe. If Hubble's
constant were 11 km/s/million light-years, the age of the universe
would be about
19) Given that the universe is about 14 billion years old, which of
the following statements is logically valid?
1) To date, physicists have investigated the behavior of matter and
energy at temperatures as high as those that existed in the universe
as far back as ________ after the Big Bang.
2) How long after the Big Bang was the Planck time, before which our
current theories are completely unable to describe conditions in the
3) The Planck era refers to the time period
5) A GUT (grand unified theory) refers to theories that
6) When we say that the electromagnetic and weak forces "freeze
out" from the electroweak force at 10-10 seconds after the Big
Bang, we mean that
7) How many forces operated in the universe during the GUT era?
8) Which forces have physicists shown to be the same force under
conditions of very high temperature or energy, as confirmed by
experiments in particle accelerators?
10) (From a science quiz that appeared in the weekly magazine The
Economist.) Economic history is easier to write than the history of
the universe. Nevertheless, most cosmologists now think that when the
universe was formed,
11) Why might inflation have occurred at the end of the GUT era?
12) What direct evidence do we have that the weak and electromagnetic
forces were once unified as a single electroweak force?
13) What happened to the quarks that existed freely during the
14) Approximately how long did the era of nucleosynthesis last?
15) What kinds of atomic nuclei formed during the era of
16) Why is the era of nucleosynthesis so important in determining the
chemical composition of the universe?
17) Why did the era of nuclei end when the universe was about 300,000
18) Evidence that the cosmic background radiation really is the
remnant of a Big Bang comes from predicting characteristics of remnant
radiation from the Big Bang and comparing these predictions with
observations. Four of the five statements below are real. Which one is
19) Which of the following statements about the cosmic background
radiation is not true?
20) Where do the photons in the cosmic background radiation
21) Why does the Big Bang theory predict that the cosmic background
radiation should have a perfect thermal radiation spectrum?
22) Why do we expect the cosmic background radiation to be almost,
but not quite, the same in all directions?
23) Helium originates from
24) What are the two key observational facts that led to widespread
acceptance of the Big Bang model?
25) Why do we think tiny quantum ripples should have been present in
the very early universe?
26) What is postulated to have caused a sudden inflation of the early
Lost in Spacetime. Just when you thought it was safe to take final
exams . . . a vindictive multi-dimensional being reaches down (up?
over? through?) to Earth and pulls you out of the universe. You are
thrown back into the universe at a place of this being's choosing, and
she permits you to leave only after you have identified your
surroundings. You are subject to several tests.
28) You find yourself in a place that looks (except for your own
presence) perfectly symmetrical. There is no way to distinguish one
place from another, and all forces are one. With this perfect
symmetry, there is no obvious way to define the flow of time. Where
29) You are in a place that is extremely hot and dense, making you
feel quite sweaty and claustrophobic. You can't see far because your
surroundings are opaque to light. Around you, nuclear fusion is
converting carbon into oxygen and other elements. Where are you?
30) You are on the surface of an object, and you have a fairly clear
view out into space. It might be very nice, except for one major
drawback: You are very squashed. Also, light you observe from distant
objects is apparently slightly blueshifted (compared to what it
normally looks like). The surface of the object is composed primarily
of carbon and oxygen, and the horizon distance is about the same as
that on Earth. By observing the stellar background for a few weeks,
you realize that there are several planets orbiting your object. Where
31) It sure is bright everywhere; you've been able to travel around a
bit, and it's clear that you are not in a star. Yet it is as bright as
looking directly at the Sun. In your extensive travels through your
current surroundings, you cannot find a single neutral atom anywhere,
nor can you find a nucleus besides hydrogen or helium. And, while it
is hot (a few thousand degrees Kelvin), it is nowhere near the
temperature needed for nuclear fusion. Where are you?
32) You are feeling like spaghetti. Although normally only about 2
meters tall, you are now about 25 meters long. (How fortunate, if
painful, that the being has arranged for your body to become elastic
enough so that it is not ripped apart under these conditions.) As you
look up over your head, you see things moving pretty quickly in the
universe–but that lasts only for a brief instant, and then all contact
with the universe is lost. Where are you?
33) You are once again in a hot, dense place. You are surrounded by
protons and neutrons, some rapidly fusing into helium. You notice that
your surroundings are cooling (good, because it's really hot!) and
rapidly dropping in density. Within about 3 minutes, the fusion
reactions stop. Where are you?
34) At last you are in a place where the heat and high density are no
longer bothering you. However, although the density is very low, the
gas around you is extremely high in temperature. In fact, the
temperature is so high that it is emitting lots of X rays, which are
creating cancer-causing mutations in your body at a rapid rate. Well,
at least the view is great! There are no stars anywhere within about
10,000 light-years of you, but at slightly greater distances your sky
is brightened by many beautiful, star-filled structures, some with
majestic spiral shapes. Where are you?
35) At last, someplace fairly comfortable. Very weak gravity is
holding you to the surface of the small object on which you sit. Your
object is apparently moving away from a star, perhaps one that it
orbits with a period of thousands of years. Around you, geysers are
spouting gas into space. Looking back along the object's orbit, you
see particles of dust that the geysers apparently blew off the object
when it was nearer to the star that it is now leaving behind. You
conclude that the geysers were recently much more active but are now
settling down into a quiescent state that may last for millennia. You
also soon realize that you are closer to home than you have been in
all your previous journeys. Perhaps if you can somehow find a small
rocket, a heat shield, and a good parachute, you can escape and head
home for your final exam. Where are you?
36) Which of the following observations is not a piece of evidence
supporting the Big Bang theory?
1) The Planck era is another name for the present period of time in the universe.
2) The observed composition of ordinary matter in the universe–roughly 75 percent hydrogen and 25 percent helium–closely matches theoretical predictions based on the Big Bang model.
3) GUT theories predict that protons will eventually decay, causing all solid objects in the universe to fall apart if the universe keeps expanding forever.
4) The theory that inflation occurred in the early universe is incompatible with the theory of relativity.
5) If inflation really occurred, then our observable universe is only a tiny portion of the entire universe born in the Big Bang.
6) Observations of the cosmic background radiation from the COBE satellite revealed tiny variations in its temperature from one place to another (corresponding to a few millionths of a degree Kelvin).
7) The Big Bang predicts that one in four atoms in the universe is helium.
8) Current measurements of the density of the universe support the prediction of the theory of inflation that the universe should be flat.
9) The fact that the sky is dark at night shows that the observable universe cannot extend forever.
10) Process of Science: Inflation can explain some general features of the Universe but it is not directly testable and cannot be considered a theory.
1) Based on our current understanding of physics, we can understand
the conditions that prevailed in the early universe as far back in
time as about
2) What happens when a particle of matter meets its corresponding
antiparticle of antimatter?
3) What is the significance of the Planck time?
4) The four fundamental forces that operate in the universe today are
5) A "GUT" (grand unified theory) refers to theories that
6) What do we mean by inflation?
7) Which of the following statements correctly summarizes the events
in the early universe according to the Big Bang theory?
9) The Big Bang theory is supported by two major lines of evidence
that alternative models have not successfully explained. What are
11) The idea of dark matter arose to explain gravitational effects
observed in galaxies and clusters of galaxies. However, studies of the
early universe (especially of the cosmic microwave background and of
chemical abundances) also tell us something about dark matter. What do
they tell us?
12) Which of the following observations cannot be explained by the
Big Bang theory unless we assume that an episode of inflation
13) The idea of inflation makes one clear prediction that, until the
discovery of an accelerating expansion, seemed to contradict the
available observations. What is this prediction?
14) Olbers's paradox is an apparently simple question, but its
resolution suggests that the universe is finite in age. What is the
15) What is the temperature of the universe (as a whole) today?
16) Which of the following statements cannot be tested by science
1) How do we determine the conditions that existed in the very early
2) Why can't current theories describe what happened during the
3) Which of the following statements best explains what we mean when
we say that the electroweak and strong forces "froze out" at
10-38 second after the Big Bang?
4) According to the Big Bang theory, how many forces—and which
ones—operated in the universe during the GUT era?
5) Laboratory experiments conducted with particle accelerators
confirm predictions made by the theory that unifies
6) What was the significance of the end of the era of
nucleosynthesis, when the universe was about 5 minutes old?
7) According to the Big Bang theory, why do we live in a universe
that is made of almost entirely of matter rather than antimatter?
8) Which of the following is not an observed characteristic of the
cosmic microwave background?
9) In principle, if we could see all the way to the cosmological
horizon we could see the Big Bang taking place. However, our view is
blocked for times prior to about 380,000 years after the Big Bang.
10) If observations had shown that the cosmic microwave background
was perfectly smooth (rather than having very slight variations in
temperature), then we would have no way to account for
11) In stars, helium can sometimes be fused into carbon and heavier
elements (in their final stages of life). Why didn't the same fusion
processes produce carbon and heavier elements in the early universe?
12) How does the idea of inflation account for the existence of the
"seeds" of density from which galaxies and other large
13) Which of the following is not consistent with recent observations
of the cosmic microwave background by the WMAP satellite?
14) Based on the results from the WMAP satellite, the overall
composition of the universe is
15) Which adjective does not necessarily describe a known feature of
the early universe? (Be sure to consider the universe as a whole, not
just the observable universe.)
16) The Big Bang theory seems to explain how elements were formed
during the first few minutes after the Big Bang. Which hypothetical
observation below (these are not real observations) would call our
current theory into question?
1) Why do we call dark matter "dark"?
2) What is meant by "dark energy"?
3) Why do we believe 90 percent of the mass of the Milky Way is in
the form of dark matter?
4) How do we know that there is much more mass in the halo of our
galaxy than in the disk?
5) What evidence suggests that the Milky Way contains dark matter?
6) If there is no dark matter in the Milky Way Galaxy, what is the
best alternative explanation for the observations?
7) How are rotation curves of spiral galaxies determined beyond radii
where starlight can be detected?
8) The distribution of the dark matter in a spiral galaxy is
9) How do we determine the amount of dark matter in elliptical
10) When we see that a spectral line of a galaxy is broadened, that
is, spanning a range of wavelengths, we conclude that
11) A large mass-to-light ratio for a galaxy indicates that
12) What is the mass-to-light ratio for the inner region of the Milky
Way Galaxy, in units of solar masses per solar luminosity?
13) Compared to the central regions of spiral galaxies, we expect
elliptical galaxies to have
14) If a galaxy's overall mass-to-light ratio is 100 solar masses per
solar luminosity, and its stars account for only 5 solar masses per
solar luminosity, how much of the galaxy's mass must be dark matter?
15) Which of the following methods used to determine the mass of a
cluster does not depend on Newton's laws of gravity?
16) Why wasn't the intracluster medium in galaxy clusters discovered
until the 1960s?
17) Which of the following statements about rich clusters of galaxies
(those with thousands of galaxies) is not true?
18) Gravitational lensing occurs when
19) Which of the following is not evidence for dark matter?
20) Which of the following particles are baryons?
21) Which of the following is an example of baryonic matter?
22) Measuring the amount of deuterium in the universe allows us to
set a limit on
23) Based on current evidence concerning the amount of deuterium in
the universe, we can conclude that
24) What do we mean when we say that a particle is a weakly
25) Why can't the dark matter in galaxies be made of neutrinos?
26) Which of the following are candidates for dark matter?
27) Why do we expect WIMPs to be distributed throughout galactic
halos, rather than settled into a disk?
28) Why isn't space expanding within systems such as our solar system
or the Milky Way?
29) What are peculiar velocities?
30) What do peculiar velocities reveal?
31) How do astronomers create three-dimensional maps of the universe?
32) What does the universe look like on very large scales?
33) What fraction of the mass needed to halt expansion is known to
exist in the form of visible mass in the universe?
34) Based on inventoried matter in the universe, including dark
matter known to exist in galaxies and clusters, the actual density of
the universe is what fraction of the critical density?
35) If all the "dark matter" in the Universe were to be,
somehow, instantaneously removed, which of the following would not
36) Which model of the universe gives the youngest age for its
37) What is the ultimate fate of an open universe?
38) Recent measurements of the expansion rate of the universe reveal
that the expansion rate of the universe is doing something astronomers
did not expect. What is that?
39) What is the evidence for an accelerating universe?
40) What might be causing the universe to accelerate?
41) What is Einstein's cosmological constant?
42) What is not a main source of evidence for the existence of dark
1) Approximately 90 percent of the mass of the Milky Way is located in the halo of the galaxy in the form of dark matter.
2) Dark matter is purely hypothetical, because we have no way of detecting its presence.
3) If the universe is accelerating, it will expand forever.
4) If we learn that the universe is a recollapsing universe, it will mean that the universe is presently contracting, rather than expanding as generally believed.
5) By definition, our Sun has a mass-to-light ratio of 1 solar mass per solar luminosity.
6) One possible ingredient of dark matter is known as WIMPs, or weakly interacting massive particles. WIMPs probably are made of protons and neutrons.
7) Although we don't know exactly when clusters, galaxies, or stars began forming, we do know that clusters came first, with galaxies and stars forming later.
8) Individual galaxies generally have higher mass-to-light ratios than clusters of galaxies.
9) Some galaxy clusters are still growing today.
10) The visible parts of galaxies contribute about one-tenth of the critical density of the universe.
11) The only possible geometry of an accelerating universe is open.
1) Which of the following best summarizes what we mean by dark
3) The text states that luminous matter in the Milky Way seems to be
much like the tip of an iceberg. This refers to the idea that
4) What is a rotation curve?
5) What is the primary way in which we determine the mass
distribution of a spiral galaxy?
6) What do we mean when we say that the rotation curve for a spiral
galaxy is "flat"?
7) Although we know less about dark matter in elliptical galaxies
than in spiral galaxies, what does current evidence suggest?
8) In general, when we compare the mass of a galaxy or cluster of
galaxies to the amount of light it emits (that is, when we look at it
mass-to-light ratio), we expect that
9) Which of the following is not one of the three main strategies
used to measure the mass of a galaxy clusters?
10) When we say that a cluster of galaxies is acting as a
gravitational lens, what do we mean?
11) Which of the following statements best summarizes current
evidence concerning dark matter in individual galaxies and in clusters
12) What is the distinguishing characteristic of what we call
ordinary or baryonic matter?
13) What do we mean when we say that particles such as neutrinos or
WIMPs are weakly interacting?
14) Which of the following best sums up current scientific thinking
about the nature of dark matter?
15) When we speak of the large-scale structure of the universe, we
16) The critical density of the universe is the
17) What is the primary form of evidence that has led astronomers to
conclude that the expansion of the universe is accelerating?
3) Spiral galaxy rotation curves are generally fairly flat out to
large distances. Suppose that spiral galaxies did not contain dark
matter. How would their rotation curves be different?
4) The flat rotation curves of spiral galaxies tell us that they
contain a lot of dark matter. Do they tell us anything about where the
dark matter is located within the galaxy?
5) It is more difficult to determine the total amount of dark matter
in an elliptical galaxy than in a spiral galaxy. Why?
6) How do we know that galaxy clusters contain a lot of mass in the
form of hot gas that fills spaces between individual galaxies?
7) Why does the temperature of the gas between galaxies in galaxy
clusters tell us about the mass of the cluster?
8) How does gravitational lensing tell us about the mass of a galaxy
9) If WIMPs really exist and make up most of the dark matter in
galaxies, which of the following is not one of their characteristics?
11) Which of the following statements about large-scale structure is
probably not true?
12) Based on current evidence, a supercluster is most likely to have
formed in regions of space where
13) Based on current evidence, how does the actual average density of
matter in the universe compare to the critical density?
14) Which of the following statements best describes the current
state of understanding regarding the apparent acceleration of the
expansion of the universe?
15) Some people wish that we lived in a recollapsing universe that
would eventually stop expanding and start contracting. For this to be
the case, which of the following would have to be true (based on
16) Hubble's constant is related to the age of the universe, but the
precise relationship depends on the way in which the expansion rate
changes with time. For a given value of Hubble's constant today (such
as 24 km/s/Mly), the age of the universe is oldest if what is true?
17) Imagine that it turns out that dark matter (not dark energy) is
made up of an unstable form of matter that decays into photons or
other forms of energy about 50 billion years from now. Based on
current understanding, how would that affect the universe at that