Deck 14: Measuring Galaxies

Question 1

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

Answer 1

0.15

Question 2

Which of the following galaxies can be found with a bar-like structure in them?

A) spiral
B) elliptical
C) irregular
D) all of the above

Answer 2

spiral

Question 3

If a galaxy has a recessional velocity of 880 km/s,what is its distance if the Hubble constant is 72 km/s/Mpc?

A) 12 Mpc
B) 27 Mpc
C) 123 Mpc
D) 2,700 Mpc

Answer 3

12 Mpc

Question 4

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 5

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 6

A galaxy that is classified as Sc would have:

A) tightly wound spiral arms and a large central bulge.
B) loosely wound spiral arms and a large central bulge.
C) tightly wound spiral arms and a small central bulge.
D) loosely wound spiral arms and a small central bulge.

Question 7

If the distance of a galaxy is 100 Mpc,what is its recessional velocity if the Hubble constant is 72 km/s/Mpc?

A) 0.72 km/s
B) 1.40 km/s
C) 1,000 km/s
D) 7,200 km/s

Question 8

If we lived on a galaxy 1 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 1 billion light-years away from us.

Question 9

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 appears 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 10

Stars that travel in the same direction around a concentration of mass are characteristic orbits found in:

A) the arms of spiral galaxies.
B) the bulges of spiral galaxies.
C) elliptical galaxies.
D) irregular galaxies.

Question 11

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 72 km/s/Mpc?

A) 39,700 km/s
B) 45,700 km/s
C) 47,000 km/s
D) 54,500 km/s

Question 12

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 13

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

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

Question 14

Besides shape,what characteristic clearly separates elliptical galaxies from spiral galaxies?

A) size
B) shape
C) age
D) color

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

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 17

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 a Hubble constant of 72 km/s/Mpc.

A) 950 Mpc
B) 1,800 Mpc
C) 2,300 Mpc
D) 1,130 Mpc

Question 18

What does the Hubble tuning fork illustrate?

A) the evolutionary sequence of galaxies
B) the locations of galaxies
C) the motions of galaxies
D) a classification scheme

Question 19

If the distance of a galaxy at a redshift z = 0.5 is 1,800 Mpc,what is H₀?

A) 3,600 km/s/Mpc
B) 0.0003 km/s/Mpc
C) 83 km/s/Mpc
D) 900 km/s/Mpc

Question 20

In the Great Debate of 1920,Curtis and Shapley argued about whether spiral and elliptical nebulae were inside or outside of the Milky Way.These objects are now known as:

A) dark matter.
B) supermassive black holes.
C) galaxies.
D) globular clusters.

Question 21

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 22

Which of the following does NOT support the existence of dark matter?

A) a super massive black hole at the galactic center
B) observed galactic rotation curves
C) the distribution of light in a galaxy
D) X-ray-emitting gas in elliptical galaxies

Question 23

What is the size of the region responsible for powering an AGN?

A) atomic size
B) stellar size
C) Solar System size
D) galaxy size

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 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 26

The figure below shows the spectrum of a star (top)whose motion compared to our star is nearly stationary within the Milky Way Galaxy.The galaxy spectrum (bottom)indicates that the galaxy is

A) moving toward us.
B) moving away from us.
C) stationary.
D) There is not enough information.

Question 27

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 28

What is a quasar?

A) an AGN powered by a supermassive black hole
B) a star that only emits radio waves
C) a star made up of quarks
D) a galaxy that has its light affected by a gravitational lens

Question 29

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 30

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 31

Astronomers use galactic redshift as a measure of:

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

Question 32

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 33

Which of the following is NOT associated with the arms of a spiral galaxy?

A) density waves
B) ongoing stellar formation
C) dust lanes
D) random stellar orbits

Question 34

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

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

Question 35

What is observed to happen to the velocities of stars that reside at greater distances from the center of the galaxy?

A) They move slower and slower.
B) They move faster and faster.
C) They vary greatly in a random fashion.
D) They essentially stay the same.

Question 36

What accounts for the different types of observed AGNs?

A) galaxy's age
B) galaxy's distance
C) galaxy's mass
D) orientation of the galaxy to our line of sight

Question 37

The Hubble 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 38

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 39

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 an AGN at their centers.

Question 40

The most likely dark matter candidate seems to be:

A) black holes
B) planets
C) neutron stars
D) neutrino-like particles

Question 41

Name the two primary classes of proposed sources of dark matter.What objects are included in each class,and which one is the most likely source of dark matter?

Question 42

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

Question 43

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

Question 44

Explain the connection between quasars and AGNs and their source of power.

Question 45

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

Question 46

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?

Question 47

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

Question 48

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 72 km/s/Mpc?

Question 49

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

Question 50

What was the Hubble tuning fork originally intended to explain,and what does it mean to astronomers today?

Question 51

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