Question 1

Galaxy peculiar velocities are typically about 300 km/s.How far away do you have to look in order to see recessional velocities that are 10 times this peculiar velocity? Note that the Hubble constant has a value of 70 km/s/Mpc.
A) 12 Mpc
B) 25 Mly
C) 37 Mpc
D) 43 Mpc
E) 52 Mpc

Accepted Answer

The recessional velocity is given by v = H0 * d, where H0 is the Hubble constant and d is the distance. We are given that the recessional velocity is 10 times the peculiar velocity, so v = 10 * 300 km/s = 3000 km/s. We are also given that H0 = 70 km/s/Mpc, so d = v / H0 = 3000 km/s / 70 km/s/Mpc = 43 Mpc.

Question 2

Cosmological redshift is redshift due to
A) the true velocity of a receding galaxy.
B) the cosmic microwave background radiation.
C) the expansion of the space that light travels through.
D) the higher abundance of hydrogen present in older galaxies.
E) light interacting with dark matter.

Accepted Answer

Cosmological redshift occurs because the universe is expanding, causing the wavelengths of light traveling through space to stretch, making them appear redshifted.

Question 3

If the distance of a galaxy is 5 Mpc, what is its recessional velocity if the Hubble constant is 70 km/s/Mpc?
A) 70 km/s
B) 100 km/s
C) 350 km/s
D) 500 km/s
E) 700 km/s

Accepted Answer

The recessional velocity can be calculated using Hubble's Law: velocity = Hubble constant × distance. Here, velocity = 70 km/s/Mpc × 5 Mpc = 350 km/s.

Question 4

The inverse of the value of H₀ gives a measurement in a unit of A) time. B) mass. C) density. D) size. E) luminosity.

Accepted Answer

The inverse of the Hubble constant (H₀) gives a measurement of time, specifically the age of the universe.

Question 5

You observe the following three galaxies and measure their respective recession velocities: A, 2,100 km/s; B, 4,400 km/s; and C, 3,050 km/s.Which of the following must be true about these galaxies?
A) A is smaller than B.
B) A has more star formation than C.
C) B has more stars than C.
D) B is farther away from us than A.
E) They are all members of the Local Group.

Accepted Answer

According to Hubble's Law, a galaxy's recession velocity is proportional to its distance from us. Therefore, a higher recession velocity indicates that galaxy B is farther away from us than galaxy A.

Question 6

The figure below uses a rubber sheet as an analogy for Hubble expansion, with coins representing galaxies.The illustration demonstrates that 
A) galaxies may be sitting still, but will move farther apart as space expands.
B) galaxies stand still, and distances are unchanged by the expanding universe.
C) galaxies are repelled from each other, causing them to move away from each other.
D) space is expanding in two dimensions only.
E) galaxies are being flung outward by the Big Bang.

Accepted Answer

The answer of The figure below uses a rubber sheet...

Question 7

Will the increasing scale factor of the universe cause the Sun to get larger over time?
A) Yes, because the scale factor will change the rate of fusion in the Sun's core.
B) Yes, because the atoms within the Sun will all expand individually.
C) No, because Earth is at center of the universe's expansion.
D) Yes, because the expansion of the universe will directly cause the Sun to expand.
E) No, because the Sun's self-gravity locally dominates over the expansion of the universe.

Accepted Answer

The expansion of the universe affects large-scale structures, but local systems like the Sun are bound by gravity, which dominates over cosmic expansion.

Question 8

The majority of the redshift that we measure from the most distant galaxies is due to
A) excess hydrogen emission.
B) most of these galaxies being old, elliptical-type galaxies.
C) the expansion of the universe "stretching" the wavelengths of photons.
D) the cosmic microwave background.
E) the actual velocity of that galaxy.

Accepted Answer

The redshift observed in distant galaxies is primarily due to the expansion of the universe, which stretches the wavelengths of photons, causing them to shift towards the red end of the spectrum. This is known as cosmological redshift.

Question 9

What would you predict for the recession velocity of a galaxy whose distance (measured with the help of Type Ia supernovae) is 42 Mpc? Note that the Hubble constant has a value of
70 km/s/Mpc.
A) 2,940 km/s
B) 1.42 km/s
C) 205,800 km/s
D) 25,000 km/s
E) 386 km/s

Accepted Answer

The recession velocity of a galaxy can be calculated using Hubble's Law: velocity = Hubble constant × distance. Here, velocity = 70 km/s/Mpc × 42 Mpc = 2,940 km/s.

Question 10

The apparent recessional velocities of galaxies at large distances are due mainly to
A) the actual motions of the galaxies through space.
B) the motion of our Sun around the galactic center.
C) a continuously increasing scaling factor of the universe.
D) the relativistic jets launched by supermassive black holes.
E) incorrect interpretation of spectra from galaxies.

Accepted Answer

The apparent recessional velocities of galaxies are primarily due to the expansion of the universe, which is described by a continuously increasing scaling factor in cosmology. This is known as the metric expansion of space, where galaxies appear to move away from us as space itself expands.

Question 11

Two galaxies are currently separated by 55 Mpc.Roughly how long did it take for them to reach this separation?
A) 13.7 billion years
B) 250 million years
C) 4.6 billion years
D) less than a second
E) 27 billion years

Accepted Answer

The current separation of galaxies is largely due to the expansion of the universe since the Big Bang, which occurred approximately 13.7 billion years ago.

Question 12

If we "reverse" Hubble expansion, we see that the universe should have been very dense in the distant past, and so it must have been ________ than it is today, and we should be able to
Observe ________ as a result.
A) much colder; cosmological redshift
B) much colder; the cosmic microwave background
C) much hotter; gravitational redshift
D) much hotter; the cosmic microwave background
E) much hotter; black holes

Accepted Answer

Reversing the Hubble expansion implies that the universe was denser and hotter in the past. This leads to the prediction and observation of the cosmic microwave background, which is the remnant radiation from the hot, dense early universe.

Question 13

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) 1 Mpc
B) 7 Mpc
C) 10 Mpc
D) 70 Mpc
E) 100 Mpc

Accepted Answer

The distance to the galaxy can be calculated using Hubble's Law: velocity = Hubble constant × distance. Rearranging gives distance = velocity / Hubble constant = 700 km/s / 70 km/s/Mpc = 10 Mpc.

Question 14

In the figure below, three identical photons were each emitted when their local scale factor was R_U =0.5.Each is then measured after the scale factor of the universe changes to a different amount, as shown.Which photon will be measured to have the greatest energy? A) the one at R_U =1 B) the one at R_U = 2 C) the one at R_U =3 D) The photons at R_U= 2 and 3 will have identical energy. E) All three will have the same energy.

Accepted Answer

The answer of In the figure below, three identical photons...

Question 15

If the slope of the graph v vs.D is H_o, the slope of the D vs.v graph is the A) age of the universe. B) cosmological constant. C) scaling factor of the universe. D) temperature of the CMB. E) amount of dark energy in the universe.

Accepted Answer

The answer of If the slope of the graph v...

Question 16

Hubble originally estimated the "Hubble constant" to be about 500 km/s/Mpc.What age of the universe would such a number imply?
A) 2 billion years
B) 13.8 billion years
C) 16 billion years
D) 250 million years
E) 500 million years

Accepted Answer

The answer of Hubble originally estimated the "Hubble constant" to...

Question 17

In the figure below, three identical photons were each emitted when their local scale factor was R_U = 0.5.Each is then measured after the scale factor of the universe changes to a different amount, as shown.Which photon will be measured to have the greatest cosmological redshift? A) the one at R_U =1 B) the one at R_U = 2 C) the one at R_U = 3 D) The photons at R_U = 2 and 3 will be identical, and have the greatest redshift. E) All three will have the same cosmological redshift.

Accepted Answer

The answer of In the figure below, three identical photons...

Question 18

The high temperature and density of the early universe are directly responsible for
A) the expansion of the universe.
B) the cosmic microwave background.
C) star formation.
D) cosmological redshift.
E) nucleosynthesis of the heaviest elements.

Accepted Answer

The high temperature and density of the early universe led to the formation of the cosmic microwave background radiation as the universe cooled and expanded.

Question 19

If you measured the distances and recessional velocities for a sample of galaxies and plotted the data to get the figure shown 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

Accepted Answer

The answer of If you measured the distances and recessional...

Question 20

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) 28 billion years.
E) 33 billion years.

Accepted Answer

The age of the universe is inversely proportional to the Hubble constant. If the Hubble constant is halved, the age of the universe would double from its current estimate of about 14 billion years, making it approximately 28 billion years.

Quiz 21: The Expanding Universe

Galaxy peculiar velocities are typically about 300 km/s.How far away do you have to look in order to see recessional velocities that are 10 times this peculiar velocity? Note that the Hubble constant has a value of 70 km/s/Mpc.

Cosmological redshift is redshift due to

If the distance of a galaxy is 5 Mpc, what is its recessional velocity if the Hubble constant is 70 km/s/Mpc?

The inverse of the value of H₀ gives a measurement in a unit of

You observe the following three galaxies and measure their respective recession velocities: A, 2,100 km/s; B, 4,400 km/s; and C, 3,050 km/s.Which of the following must be true about these galaxies?

The figure below uses a rubber sheet as an analogy for Hubble expansion, with coins representing galaxies.The illustration demonstrates that

Will the increasing scale factor of the universe cause the Sun to get larger over time?

The majority of the redshift that we measure from the most distant galaxies is due to

What would you predict for the recession velocity of a galaxy whose distance (measured with the help of Type Ia supernovae) is 42 Mpc? Note that the Hubble constant has a value of 70 km/s/Mpc.

The apparent recessional velocities of galaxies at large distances are due mainly to

Two galaxies are currently separated by 55 Mpc.Roughly how long did it take for them to reach this separation?

If we "reverse" Hubble expansion, we see that the universe should have been very dense in the distant past, and so it must have been than it is today, and we should be able to Observe as a result.

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

In the figure below, three identical photons were each emitted when their local scale factor was R_U =0.5.Each is then measured after the scale factor of the universe changes to a different amount, as shown.Which photon will be measured to have the greatest energy?

If the slope of the graph v vs.D is H_o, the slope of the D vs.v graph is the

Hubble originally estimated the "Hubble constant" to be about 500 km/s/Mpc.What age of the universe would such a number imply?

In the figure below, three identical photons were each emitted when their local scale factor was R_U = 0.5.Each is then measured after the scale factor of the universe changes to a different amount, as shown.Which photon will be measured to have the greatest cosmological redshift?

The high temperature and density of the early universe are directly responsible for

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

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