Deck 18: Our Expanding Universe

Question 1

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

Answer 1

False

Question 2

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

A) 30 years.
B) 90 years.
C) 150 years.
D) 300 years.

Answer 2

90 years.

Question 3

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

Answer 3

True

Question 4

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

Question 5

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 6

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 the same no matter where 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.

Question 7

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

Question 8

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

Question 9

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

Question 10

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

Question 11

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

Question 12

The standard Big Bang theory successfully predicts that the fraction of helium by mass in the primordial universe was 2 percent.

Question 13

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 spiral nebulae were located outside the Milky Way.
D) life existed outside of Earth.

Question 14

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

Question 15

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 the Cepheids.

Question 16

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.

Question 17

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

Question 18

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

Question 19

The Cosmological Principle says that physical laws that are true in one part of the universe must be true in every part of the universe.

Question 20

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

Question 21

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 supernova 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.

Question 22

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.

Question 23

Why are some galaxies' spectra blueshifted rather than redshifted?

A) Some distant galaxies are gravitationally lensed.
B) Some nearby galaxies are attracted to us because of the mass of the Milky Way.
C) Some nearby galaxies have vigorous star formation and are much bluer than others.
D) Some distant galaxies have AGN at their centers.

Question 24

Galaxies move away from us in all directions because

A) the force of gravity strengthens with distance.
B) the force of gravity weakens with distance.
C) space is expanding.
D) our galaxy has expelled all other galaxies.

Question 25

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

A) Cepheids
B) Parallax
C) Type I supernovae
D) Main-sequence fitting

Question 26

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

Question 27

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?

A) 950 Mly
B) 1,800 Mly
C) 2,300 Mly
D) 3,700 Mly

Question 28

Hubble's constant, ,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.

Question 29

If suddenly we find that the distance between Earth and the Sun is now 10 percent larger than we thought it was before,what else will change?

A) The distances of stars
B) The size of our galaxy
C) The value of
D) All of the above

Question 30

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

A) 0.01
B) 0.05
C) 0.10
D) 0.15

Question 31

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

Question 32

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/Mly
B) 22 km/s/Mly
C) 45 km/s/Mly
D) 100 km/s/Mly

Question 33

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 faintest galaxies look redder because their stars are younger.
C) Helium,lithium,and beryllium were made as the universe cooled after the initial Big Bang.
D) The early universe was very hot and dense.

Question 34

If the distance of a galaxy is 100 Mly,what is its recessional velocity if the Hubble constant is 22 km/s/Mly?

A) 100 km/s
B) 220 km/s
C) 1,000 km/s
D) 2,200 km/s

Question 35

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

Question 36

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 22 km/s/Mly? Note that the rest wavelength of the H $\alpha$ emission line is 656.3 nm.

A) 1,120 km/s
B) 2,080 km/s
C) 6,070 km/s
D) 8,500 km/s

Question 37

If we lived on 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 today
D) Nothing-there are no galaxies one billion light-years away from us.

Question 38

Astronomers use galactic redshift as a measure of

A) gravity.
B) distance.
C) velocity.
D) mass.

Question 39

If a galaxy has a recessional velocity of 880 km/s,what is its distance if the Hubble constant is 22 km/s/Mly?

A) 40 Mly
B) 88 Mly
C) 400 Mly
D) 8,800 Mly

Question 40

To be a standard candle an object must have a constant

A) lifetime.
B) brightness.
C) luminosity.
D) distance.

Question 41

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 22 km/s/Mly? Note that the rest wavelength of the H $\alpha$ emission line is 656.3 nm.

Question 42

The most distant galaxies we can see today have a redshift of when the universe was

A) 3 times smaller than it is today.
B) 7 times smaller than it is today.
C) 12 times smaller than it is today.
D) the same size as it is today.

Question 43

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

Question 44

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) 1 $\mu$ m.
B) 10 $\mu$ m.
C) 100 $\mu$ m.
D) 1,000 $\mu$ m.

Question 45

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

Question 46

The CBR is a snapshot of the radiation in the universe at a redshift of when the universe was

A) 1,000 times smaller than it is today.
B) 10 times smaller than it is today.
C) 2 times smaller than it is today.
D) the same size as it is today.

Question 47

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

Question 48

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

Question 49

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) deuterium
D) helium

Question 50

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

A) Helium
B) Lithium
C) Carbon
D) Deuterium

Question 51

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 .
B) From redshifts of to 100,photons are gravitationally lensed by the dark matter in the universe.
C) At redshifts of ,most of the photons are blocked by large amounts of cold gas and dust.
D) For redshifts of ,photons are heavily altered because they easily react with individual protons and electrons in the universe.

Question 52

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

Question 53

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

A) Photons began to travel freely through the universe.
B) Neutrinos ceased to interact with normal matter.
C) Dark matter ceased to interact with normal matter.
D) Protons and neutrons combined to form nuclei such as deuterium and helium.

Question 54

If the distance of a galaxy at a redshift 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

Question 55

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.

Question 56

The inverse of the value of is a

A) time.
B) mass.
C) density.
D) size.

Question 57

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 58

Assuming a Hubble time of 13.6 billion years and a constant rate of expansion of the universe,what was the scale factor of the universe 10.2 billion years ago (compared to today)?

A) 0.25
B) 0.50
C) 0.67
D) 0.75

Question 59

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

Question 60

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.

Question 61

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

Question 62

Assuming the Hubble constant is equal to 22 km/s/Mly,estimate the age of the universe (or Hubble time).Note that and .

Question 63

The Hubble Space Telescope can be used to study galaxies at a redshift equal to 2.How much has the universe expanded since that redshift?

Question 64

Does Hubble's law imply that our galaxy is sitting at the center of the universe? Explain.

Question 65

The COBE and WMAP satellites detected fluctuations in the CBR.On average,how big were these fluctuations,and what does that tell us about the universe at a redshift of ?

Question 66

If the density of normal matter,such as protons and electrons,were higher in the early universe,would there have been more or less made in the Big Bang?

Question 67

What important event in the universe's history marked the creation of the cosmic background radiation?

Question 68

Name two predictions of the standard Big Bang theory that have been verified by observations.

Question 69

What does the value of ,the scale factor,tell us?

Question 70

The cosmic background radiation (CBR)has a temperature of approximately 2.7 K and a Planck blackbody spectrum.Calculate the wavelength where the CBR spectrum peaks.