Deck 14: The Expansion of Space

Question 1

The figure below indicates a possible picture of a theoretical universe with two separate observers within it.Which of the following statements describes this universe?

A) This universe is homogeneous but not isotropic.
B) This universe is isotropic but not homogeneous.
C) This universe is both homogeneous and isotropic.
D) This universe is neither homogeneous nor isotropic.

Answer 1

This universe is homogeneous but not isotropic.

Question 2

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.

Answer 2

True

Question 3

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.

Answer 3

True

Question 4

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

Question 5

Edwin Hubble revolutionized astronomy when he made an accurate calculation of the distance to the Andromeda Nebula by spotting a rare Type Ia supernova.

Question 6

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

Question 7

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

Question 8

The cosmic microwave background radiation contains photons left over from the epoch in the universe's history when electrons recombined with nuclei.

Question 9

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 10

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

Question 11

The figure below shows the spectrum of a star whose motion compared to our star is nearly stationary within the Milky Way Galaxy.The shift in the galaxy spectrum indicates that the galaxy is moving quickly toward our own.

Question 12

The figure below indicates a possible picture of a theoretical universe with two separate observers within it.Which of the following statements describes this universe?

A) This universe is homogeneous but not isotropic.
B) This universe is isotropic but not homogeneous.
C) This universe is both homogeneous and isotropic.
D) This universe is neither homogeneous nor isotropic.

Question 13

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

Question 14

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

Question 15

The figure below indicates a possible picture of a theoretical universe with two separate observers within it.Which of the following statements describes this universe?

A) This universe is homogeneous but not isotropic.
B) This universe is isotropic but not homogeneous.
C) This universe is both homogeneous and isotropic.
D) This universe is neither homogeneous nor isotropic.

Question 16

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 17

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

Question 18

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

Question 19

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

Question 20

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

Question 21

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 22

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

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

Question 23

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 24

Type Ia supernovae have an absolute magnitude of -20.If you discover a Type Ia supernova 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 25

The figure below indicates a possible picture of a theoretical universe filled with galaxies moving as shown with two separate observers within it.Which of the following statements describes this universe?

A) This universe is homogeneous but not isotropic.
B) This universe is isotropic but not homogeneous.
C) This universe is both homogeneous and isotropic.
D) This universe is neither homogeneous nor isotropic.

Question 26

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

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

Question 27

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 28

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 H₀
D) All of the above

Question 29

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

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

Question 30

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 Ia supernovae
C) Globular clusters
D) Red Giant stars

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 Ia supernovae
B) Parallax,main-sequence fitting,Cepheids,Type Ia supernovae
C) Parallax,main-sequence fitting,Type Ia supernovae,Cepheids
D) Main-sequence fitting,parallax,Cepheids,Type Ia 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

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

Question 34

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 35

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 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

Question 37

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

Question 38

Astronomers use galactic redshift as a measure of:

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

Question 39

The inverse of the value of H₀ is a:

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

Question 40

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 41

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 42

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

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

Question 43

After the Big Bang,as the universe cooled and protons and electrons combined so that the universe became 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 44

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

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

Question 45

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 46

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

Question 47

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

Question 48

If you found a galaxy with a hydrogen emission line,normally found at 656.3 nm,with a measured wavelength of 756.3 nm,what would be the galaxy's redshift?

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

Question 49

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 50

In the early 1960s,physicists named Penzias and Wilson detected a persistent noise at a wavelength of 1 mm in their radio telescope. The persistent noise that Penzias and Wilson detected 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 51

The cosmic microwave background radiation 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) 2 times smaller than it is today
D) the same size as it is today

Question 52

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 53

If you found a galaxy with a hydrogen emission line,normally found at 656.3 nm,with a measured wavelength of 756.3 nm,what would the galaxy's recessional velocity be if the Hubble constant is 22 km/s/Mly?

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

Question 54

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

Question 55

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

Question 56

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 $\approx$ 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 > 1,000,most of the photons are blocked by large amounts of cold gas and dust.
D) For redshifts of z > 1,000,photons are heavily altered because they easily react with individual protons and electrons in the universe.

Question 57

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

A) In Type II supernovae 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 58

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 59

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 60

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 61

If the density of normal matter,such as protons and electrons,were higher in the early universe,would there have been more or less ⁴He made in the Big Bang?

Question 62

Assuming the Hubble constant is equal to 22 km/s/Mly,estimate the age of the universe (or Hubble time).Note that 1 Mly = 9.5 × 10¹⁸ km and 1 year = 3.17 × 10⁷ s.

Question 63

The spectrum of a galaxy is observed to have a hydrogen emission line,normally found at 656.3 nm,with a measured wavelength of 856.3 nm.What is its distance if the Hubble constant is 22 km/s/Mly?

Question 64

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.

Question 65

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

Question 66

Examine the figure below.Describe why the distance ladder is so important to the field of cosmology.

Question 67

Name three "rungs" in the distance ladder that let us estimate the value of H₀.

Question 68

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

Question 69

The COBE and WMAP satellites (see the figure below)detected fluctuations in the CBR.On average,how big were these fluctuations,and what does that tell us about the very early universe?

Question 70

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

Question 71

The spectrum of a galaxy is observed to have a hydrogen emission line,normally found at 656.3 nm,with a measured wavelength of 928.7 nm.What is its redshift?