Deck 19: The Expanding Universe

Question 1

We can measure the value of H₀ directly with no intermediate steps.

Answer 1

False

Question 2

The cosmological principle says physical laws that the universe is homogeneous and isotropic.

Answer 2

True

Question 3

The current temperature of the cosmic microwave background radiation is 17 K.

Answer 3

False

Question 4

The apparent recessional velocities of galaxies at large distances are due mainly to the actual motions of the galaxies through space.

Question 5

The value of the scale factor R_U depends inversely on the value of redshift z.

Question 6

Charles Messier published the first galaxy catalog containing over 2,000 nearby galaxies.

Question 7

What do astronomers mean when they say that the universe is homogeneous?

A) All stars in all galaxies have planetary systems just like ours.
B) The universe looks exactly the same no matter what place you look.
C) Galaxies are generally distributed similarly throughout the universe.
D) Generally speaking, there is little difference between conditions on Earth, in the Sun, or in outer space.
E) The universe looks the same at all times in its history.

Question 8

Astronomers have known that galaxies are separate entities outside of our own for roughly the last:

A) 35 years
B) 60 years
C) 90 years
D) 150 years
E) 210 years

Question 9

In the Great Debate of 1920, Curtis argued that spiral nebulae were individual galaxies, while Shapley argued spiral nebulae must be part of the Milky Way because the Milky Way was very large in size.

Question 10

What did Edwin Hubble study in the Andromeda Galaxy that proved it was an individual galaxy and not part of our own Milky Way?

A) Cepheid stars
B) Type I supernovae
C) globular clusters
D) red giant stars
E) RR Lyrae variables

Question 11

The CMB contains photons left over from the epoch in the universe's history when electrons recombined with nuclei.

Question 12

When we measure distances to very faint galaxies with Type I supernovae, the accuracy of the measurement is only as good as that of the calibration of Cepheid stars.

Question 13

It is possible for a galaxy to have an apparent recessional velocity greater than the speed of light.

Question 14

What caused early astronomers to believe that our galaxy is only about 6,000 light-years across?

A) Telescopes were not powerful enough to observe stars farther away.
B) Interstellar dust blocked visible light from stars farther away.
C) Stars farther away could not be resolved as individual objects.
D) Astronomers miscalculated the distances to stars, believing that the stars were 50 times closer than they actually were.
E) Astronomers assumed all red stars were faint main-sequence stars, and they confused more luminous red giants with them.

Question 15

As the universe expands, the sizes of galaxies expand a measurable amount as well.

Question 16

The abundance of various elements formed from Big Bang nucleosynthesis depended only on the temperature of normal matter in the early universe.

Question 17

There is no special center to the expansion of the universe.

Question 18

In the Great Debate of 1920, Curtis and Shapley argued over whether or not:

A) the Big Bang occurred
B) the age of the universe was 14 billion years
C) the universe was contracting
D) life existed outside of Earth
E) the spiral nebulae were located outside the Milky Way

Question 19

The only chemical elements that formed as the universe cooled down after the Big Bang were hydrogen, deuterium, and helium.

Question 20

The standard Big Bang theory successfully predicts that the fraction of helium by mass in the primordial universe was 2 percent, similar to what it is in the Sun.

Question 21

If a galaxy has a recessional velocity of 50,000 km/s, at what wavelength will you observe the H $\alpha$ emission line? Note that the rest wavelength of the H $\alpha$ emission line is 656.3 nm.

A) 695.7 nm
B) 719.4 nm
C) 742.3 nm
D) 766.0 nm
E) 1750 nm

Question 22

If suddenly we find that the distances between the Sun and nearby stars are now 10 percent larger than we thought it was before, what measured properties will we not have to adjust?

A) the distances of stars
B) the size of our galaxy
C) the value of H₀
D) the fact that the universe is expanding
E) the luminosity of Type II supernovae

Question 23

Astronomers use galactic redshift as a measure of:

A) gravity
B) luminosity
C) velocity
D) mass
E) distance

Question 24

If you measured the distances and recessional velocities for a sample of galaxies and plotted the data to get the figure below, what value would you derive for the Hubble constant?

A) 10 km/s/Mpc
B) 50 km/s/Mpc
C) 70 km/s/Mpc
D) 100 km/s/Mpc
E) 500 km/s/Mpc

Question 25

If you found a galaxy with an H $\alpha$ emission line that had a wavelength of 756.3 nm, what would be the galaxy's redshift? Note that the rest wavelength of the H $\alpha$ emission line is 656.3 nm.

A) 0.05
B) 0.07
C) 0.10
D) 0.13
E) 0.15

Question 26

If the distance of a galaxy is 10 Mpc, what is its recessional velocity if the Hubble constant is 70 km/s/Mpc?

A) 700 km/s
B) 1,000 km/s
C) 3,500 km/s
D) 5,000 km/s
E) 7,000 km/s

Question 27

If a galaxy has an apparent velocity of 700 km/s, what is its distance if the Hubble constant is 70 km/s/Mpc?

A) 10 Mpc
B) 70 Mpc
C) 100 Mpc
D) 700 Mpc
E) 1,000 Mpc

Question 28

If the spectrum of a distant galaxy is observed to have a calcium K absorption line that occurs at a wavelength of 500.4 nm, what is this galaxy's distance if the rest wavelength of this absorption line is 393.4 nm? Assume the Hubble constant is 70 km/s/Mpc.

A) 720 Mpc
B) 950 Mpc
C) 1,200 Mpc
D) 2,500 Mpc
E) 3,700 Mpc

Question 29

In an imaginary universe, astronomers find that there are thousands of galaxies within a few million light years, but beyond those galaxies there is nothing but empty space. Such a universe would be:

A) isotropic and homogeneous
B) isotropic but not homogenous
C) homogeneous but not isotropic
D) neither homogeneous nor isotropic
E) lacking any evidence for the Big Bang

Question 30

To be a standard candle, an object must have a constant:

A) lifetime
B) brightness
C) luminosity
D) distance
E) mass

Question 31

Galaxies move away from us in all directions because:

A) the force of gravity increases with distance
B) the force of gravity weakens with distance
C) space is expanding
D) our galaxy has expelled all other galaxies
E) we are at the center of the expansion of the universe

Question 32

Which of the following lists distance indicators that are used to measure distances ranging from the very nearest to the very farthest?

A) Cepheids, parallax, main-sequence fitting, Type I supernovae
B) parallax, main-sequence fitting, Cepheids, Type I supernovae
C) parallax, main-sequence fitting, Type I supernovae, Cepheids
D) main-sequence fitting, parallax, Cepheids, Type I supernovae
E) Cepheids, Type I supernovae, main-sequence fitting, parallax

Question 33

What do astronomers mean when they say that the universe is isotropic?

A) Far away parts of the universe look just like nearby parts.
B) All galaxies are spiral galaxies like our own.
C) Intergalactic gas has the same density everywhere in the universe.
D) The laws of physics apply everywhere in the universe.
E) The universe looks the same no matter what direction you look.

Question 34

If we lived in a galaxy one billion light-years from our own, what would we see?

A) a universe 1 billion years younger than ours
B) a universe 1 billion years older than ours
C) much the same universe we see here
D) the universe is expanding at a slower rate than we see from Earth
E) the universe is expanding at a faster rate than we see from Earth

Question 35

According to Hubble's law, as the distance of a galaxy __________ its __________ increases.

A) increases; luminosity
B) increases; recessional velocity
C) decreases; luminosity
D) decreases; recessional velocity
E) decreases; peculiar velocity

Question 36

Hubble's constant, H₀, represents:

A) the rate of expansion of the universe
B) the speed at which galaxies are moving away from us
C) the time it takes a galaxy to move twice as far away from us
D) the size of the universe
E) the amount of time since the Solar System formed

Question 37

You see a galaxy in which the H $\alpha$ line (rest wavelength= 656.3 nm) is observed at a wavelength of 756.3 nm. What would be the observed wavelength of a particular helium line, which has a rest wavelength of 1,083 nm?

A) 1,083 nm
B) 1,183 nm
C) 1,248 nm
D) 1,440 nm
E) 3,142 nm

Question 38

The spectra of most galaxies tell us that:

A) most galaxies appear to be moving away from us
B) their light comes predominantly from objects other than stars
C) most galaxies contain clouds of gas that are absorbing their favorite wavelengths
D) galaxies in the past rotated at a faster rate than they do today
E) galaxies are rushing through space at high speeds

Question 39

If you found a galaxy with an H $\alpha$ emission line that had a wavelength of 756.3 nm, what would be the galaxy's distance if the Hubble constant is 70 km/s/Mpc? Note that the rest wavelength of the H $\alpha$ emission line is 656.3 nm.

A) 650 Mpc
B) 760 Mpc
C) 3,200 Mpc
D) 6,400 Mpc
E) 7,600 Mpc

Question 40

In the figure shown below, the upper spectrum is from hydrogen at rest in a laboratory, and the lower spectrum is from a galaxy. How far away is this galaxy?

A) 110 Mpc
B) 170 Mpc
C) 230 Mpc
D) 280 Mpc
E) 340 Mpc

Question 41

The existence of the cosmic background radiation tells us that the early universe was:

A) much hotter than it is today
B) much colder than it is today
C) composed entirely of radiation at early times
D) composed entirely of stars at early times
E) about the same temperature as today, but was much more dense

Question 42

Where in the universe did the Big Bang take place?

A) near the Milky Way Galaxy
B) near the Virgo cluster
C) near some unknown location on the other side of the universe
D) everywhere in the universe
E) at the center of the universe, not too far from the center of the cosmic background radiation

Question 43

Which of the following is NOT a prediction of the standard Big Bang theory that has been successfully verified by observations?

A) The universe is expanding.
B) The most distant galaxies are redder because they are older.
C) Helium and lithium were made as the universe cooled after the initial Big Bang.
D) The early universe was very hot and dense.
E) The most distant galaxies are redder because their light has been stretched during the time it took for the light to reach Earth.

Question 44

What is the interpretation of a redshift larger than 1?

A) The object is moving faster than the speed of light.
B) The universe has more than doubled in size since the light from that object was emitted.
C) The object has an extremely large peculiar velocity.
D) The light was shifted to longer wavelengths from gravitational radiation.
E) The rate of expansion of the universe is increasing.

Question 45

Why can Type I supernovae be used to determine a galaxy's distance?

A) Type I supernovae occur only in very luminous galaxies.
B) Type I supernovae have approximately the same luminosity.
C) Type I supernovae have approximately the same size.
D) A Type I supernova occurs in a typical galaxy about once every 100 years.
E) Type I supernovae occur even in very small galaxies.

Question 46

Why are some galaxies' spectra blueshifted rather than redshifted?

A) Some distant galaxies are gravitationally lensed.
B) Some distant galaxies show the universe was contracting before the Big Bang started.
C) Some nearby galaxies have vigorous star formation and are much bluer than others.
D) Some distant galaxies have AGN at their centers.
E) Some nearby galaxies have small peculiar velocities in our direction.

Question 47

Which distance indicator can be used to measure the most distant objects?

A) Cepheids
B) parallax
C) Type I supernovae
D) main-sequence fitting
E) RR Lyrae stars

Question 48

In the early 1960s, physicists named Penzias and Wilson detected a persistent noise at a wavelength of 1 mm in their radio telescope that came from all directions in the sky due to:

A) synchrotron emission from the Crab Nebula
B) emission from newly formed stars in the Orion Nebula
C) cellphone usage
D) photons left over from the Big Bang
E) television and radio broadcasting

Question 49

If the Hubble constant had a value that was half of its current measured value of 70 km/s/Mpc, the age of the Universe would be about

A) 7 billion years
B) 14 billion years
C) 22 billion years
D) 27 billion years
E) 33 billion years

Question 50

The inverse of the value of H₀ is a:

A) time
B) mass
C) density
D) size
E) luminosity

Question 51

Type I supernovae have an absolute magnitude of -20. If you discover a Type I supernovae in a distant galaxy that has an apparent magnitude of 22, then how far away is this galaxy?

A) 0.3 Mpc
B) 40 Mpc
C) 1,200 Mpc
D) 2,500 Mpc
E) 3,500 Mpc

Question 52

If the distance of a galaxy at a redshift z = 0.5 is 1,800 Mpc, how many years back into the past are we looking when we observe this galaxy?

A) 500 million years
B) 2 billion years
C) 6 billion years
D) 9 billion years
E) 10 billion years

Question 53

Will the Sun get larger over many billions of years?

A) Yes, because of changes taking place in its interior.
B) Yes, because the rate of expansion of the universe is increasing.
C) No, because the Earth is at center of the universe's expansion.
D) Yes, because of the expansion of the universe is pulling the Sun apart.
E) No. It has always been the same size.

Question 54

The cosmic microwave background radiation was emitted when the universe had a size about 1/1000 of today's value. What was the temperature of the microwave background radiation when it was emitted?

A) 30 K
B) 300 K
C) 3000 K
D) 30,000 K
E) 300,000 K

Question 55

The CMB is a snapshot of the radiation in the universe at a redshift of z $\approx$ 1,000 when the universe was:

A) 1,000 times smaller than it is today
B) 10 times smaller than it is today
C) two times smaller than it is today
D) the same size as it is today
E) 10 times larger than it is today

Question 56

Distant galaxies we can see today with a redshift of z $\approx$ 6 emitted their light when the universe was:

A) five times smaller than it is today
B) six times smaller than it is today
C) seven times smaller than it is today
D) eight times smaller than it is today
E) the same size as it is today

Question 57

Galaxy peculiar velocities are typically about 300 km/s. How far away do you have to look in order to see galaxies recessional velocities that are 10 times this peculiar velocity?

A) 12 Mpc
B) 25 Mly
C) 37 Mpc
D) 43 Mpc
E) 52 Mpc

Question 58

Is dark energy responsible for the expansion of the universe?

A) No. The expansion would happen without dark energy, but dark energy is causing the expansion rate to decrease.
B) Yes. Dark energy is currently the driving force in the universe's expansion.
C) No. Dark energy is only responsible for the observed rapid motions of stars within galaxies.
D) No. The expansion would happen without dark energy, but dark energy is causing the expansion rate to increase.
E) No. The dark energy has no effect on the expansion.

Question 59

Suppose the expansion of the whole universe began only about 2 billion years ago, and before that the universe was static and not expanding. What should we expect in such a situation?

A) We would see redshifts increasing with distance until a distance of approximately 2 billion light years.
B) We would see a universe that was isotropic but not homogenous.
C) Distant galaxies would be much smaller than our own, since they have not been expanding for 13 billion years.
D) The cosmic microwave background would be perfectly uniform in temperature.
E) We would not expect evidence for a Big Bang.

Question 60

When we look at galaxies in the universe and measure their star formation rates, we find that galaxies at redshifts z $\approx$ 1 have higher star formation rates than they do now. At that time, the universe was __________ times the size it is today.

A) 0.1
B) 0.2
C) 0.5
D) 0.7
E) 0.90

Question 61

If the wavelength of the background radiation peaked at 1 $\mu$ m at the time of recombination, how old was the universe then compared to its age today?

A) 1/10th as old
B) 1/100th as old
C) 1/1,000th as old
D) 1/10,000th as old
E) 1/100,000 as old

Question 62

The spectrum of a galaxy is observed to have an H $\alpha$ emission line at a wavelength of 928.7 nm. What is its redshift? Note that the rest wavelength of the H $\alpha$ emission line is 656.3 nm.

Question 63

The figure below shows the current measurements of the abundances of various light elements in the universe (vertical yellow bar), along with theoretical predictions. If you redetermined the abundance of ordinary helium (4He) and it was 90% of the current value, what would you conclude about the density of normal matter in today's universe?

A) It would be higher, and all the various density indicators would agree.
B) It would be higher, but the various density indicators would disagree.
C) It would be lower, but the various density indicators would disagree about its value.
D) It would be lower, but the various density indicators would agree.
E) It would be about the same as current observations suggest.

Question 64

Order the following objects by the maximum distance they can be detected: Cepheid variables, RR Lyrae stars, Type I supernovae, and low-mass main-sequence stars. Explain your reasoning.

Question 65

The current temperature of the cosmic background radiation of 2.73 K means that the peak of its spectrum occurs at a wavelength of:

A) 0.1 $\mu$ m
B) 1 $\mu$ m
C) 10 $\mu$ m
D) 100 $\mu$ m
E) 1,000 $\mu$ m

Question 66

Describe the two assumptions regarding the universe that the cosmological principle makes.

Question 67

Why is it not possible to look all the way back to the Big Bang itself?

A) Photons are not produced until the stars begin to shine at a redshift of z = 20.
B) From redshifts of z =0 to 100, photons are gravitationally lensed by the dark matter in the universe.
C) At redshifts of z $\gt$ 1,000, most of the photons are blocked by large amounts of cold gas and dust.
D) For redshifts of z $\gt$ 1,000, photons are heavily altered because they easily react with individual protons and electrons in the universe.
E) Photons from the Big Bang would be so strongly redshifted that we could never detect them.

Question 68

How did Edwin Hubble definitively prove that "spiral nebulae" were individual galaxies that were separate from the Milky Way?

Question 69

Which of the following was NOT created as a result of Big Bang nucleosynthesis?

A) helium
B) lithium
C) hydrogen
D) deuterium
E) carbon

Question 70

We see the universe around us expanding, which gives distant galaxies an apparent velocity of 70 km/s/Mpc. If you were an astronomer living today in a galaxy that was located 1 billion light years away from us, at what rate would you see the galaxies moving away from you?

Question 71

Name three "rungs" in the distance ladder that let us estimate the value of the Hubble constant.

Question 72

If the Hubble constant were equal to 50 km/s/Mpc, what would the approximate age of the universe (the Hubble time) be, assuming that the expansion rate has stayed approximately constant over time? Note that 1 Mpc = 3.1 * 10¹⁹ km and 1 year = 3.17 * 10⁷ s.

Question 73

The temperature of the CMB is hotter on one side of the sky than on the other by approximately 3 mK. What does this tell us?

A) The Earth has a peculiar velocity of about 8,000 km/s with respect to the CMB.
B) The Earth has a peculiar velocity of about 400 km/s with respect to the CMB.
C) The Earth is near the center of the universe's expansion, but not exactly at the middle.
D) The universe is expanding faster on one side of us than the other.
E) The universe is homogeneous but not isotropic.

Question 74

The Sun is 27 percent helium by mass. Where was the majority of this helium manufactured?

A) in Type II supernovae explosions that happened before the Sun formed
B) in low-mass stars that lived and died before the Sun formed
C) in nuclear burning that happened in the Sun's core
D) in the Big Bang
E) by accreting Jupiter-mass planets in the early era of the Solar System

Question 75

The spectrum of a galaxy is observed to have an H $\alpha$ emission line at a wavelength of 856.3 nm. What is its distance if the Hubble constant is 70 km/s/Mpc? Note that the rest wavelength of the H $\alpha$ emission line is 656.3 nm.

Question 76

What were the positions taken by Heber Curtis and Harlow Shapley in their "Great Debate," and how were both of them partially correct?

Question 77

What is a standard candle, and why is it useful for measuring distances?

Question 78

After the Big Bang, as the universe cooled and protons and electrons combined so that the universe became neutral, what important consequence happened?

A) Protons and neutrons combined to form nuclei such as deuterium and helium.
B) Neutrinos ceased to interact with normal matter.
C) Dark matter ceased to interact with normal matter.
D) Photons began to travel freely through the universe.
E) Lithium and other light elements were formed by the fusion of hydrogen and helium.

Question 79

Does the temperature of the cosmic background radiation tell us about the age of the universe?

A) Yes, since it was produced at a redshift of approximately 1,000.
B) No, we still need to know the Hubble constant to know the universe's age.
C) No, the temperature does not but the size of temperature variations in the CMB does tell us the age.
D) Yes, in combination with information on cosmic nucleosynthesis.
E) No, the CMB formed at a wide variety of times and gives no information on the age of the whole universe.

Question 80

If there were more baryons in the universe immediately after the Big Bang, then the abundance of __________ in stars and galaxies would be higher.

A) hydrogen
B) carbon
C) uranium
D) helium
E) oxygen