Chapter 20- Galaxies and the Foundations of Modern Cosmology

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Based on counting the number of galaxies in a small patch of the sky and multiplying by the number of such patches needed to cover the entire sky, the total number of galaxies in the observable universe is estimated to be approximately

A) 100 million.

B) 1 billion.

C) 10 billion.

D) 100 billion.

E) 1 trillion.

D) 100 billion.

Suppose that we look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest?

A) the one that is reddest in color

B) the one that is bluest in color

C) the one that is farthest away

D) the one that is closest to us

E) the one that appears smallest in size

C) the one that is farthest away

Which of the following types of galaxies are most spherical in shape?

A) spirals

B) ellipticals

C) lenticulars

D) irregulars

B) ellipticals

Which of the following types of galaxies are reddest in color?

A) spirals

B) ellipticals

C) lenticulars

D) irregulars

B) ellipticals

Which of the following statements about galaxies is true?

A) Small galaxies outnumber large galaxies and produce most of the light in the universe.

B) Small galaxies outnumber large galaxies but large galaxies produce most of the light in the universe.

C) There is an approximately equal number of small and large galaxies in the universe and together they each contribute an equal amount of light.

D) Most galaxies in the universe are about the same size as the Milky Way.

E) Galaxies come in a wide variety of shapes and sizes but are all very blue in color.

B) Small galaxies outnumber large galaxies but large galaxies produce most of the light in the universe.

Which types of galaxies have a clearly defined spheroidal component?

A) spirals only

B) ellipticals only

C) lenticulars only

D) irregulars only

E) all but irregulars

E) all but irregulars

Which types of galaxies have a clearly defined disk component?

A) spirals only

B) ellipticals only

C) lenticulars only

D) irregulars only

E) spirals and lenticulars

E) spirals and lenticulars

Compared to spiral galaxies, elliptical galaxies are

A) redder and rounder.

B) redder and flattened.

C) bluer and rounder.

D) bluer and flattened.

E) always much smaller.

A) redder and rounder.

The disk component of a spiral galaxy includes which of the following parts?

A) halo

B) bulge

C) spiral arms

D) globular clusters

E) all of the above

C) spiral arms

How does a lenticular galaxy differ from a normal spiral galaxy?

A) It has no bulge.

B) It has an elongated bulge resembling a bar more than a sphere.

C) It is flatter in shape.

D) It has no gas or dust.

E) It has no spiral arms.

E) It has no spiral arms.

What is the major difference between an elliptical galaxy and a spiral galaxy?

A) A spiral galaxy contains mostly younger stars.

B) A spiral galaxy has a spherical halo.

C) An elliptical galaxy lacks a disk component.

D) Elliptical galaxies are not as big as spiral galaxies.

E) There are no dwarf spiral galaxies, but there are dwarf ellipticals.

C) An elliptical galaxy lacks a disk component.

Most large galaxies in the universe are

A) elliptical.

B) spiral or lenticular.

C)irregular.

D) abnormal.

B) spiral or lenticular.

Which of the following types of galaxies are most commonly found in large clusters?

A) spirals

B) ellipticals

C) lenticulars

D) irregulars

B) ellipticals

Approximately how many stars does a dwarf elliptical galaxy have?

A) 1 trillion

B) 100 billion

C) 10 billion

D) less than a billion

E) less than a million

D) less than a billion

Which of the following is true about irregular galaxies?

A) They are composed solely of old stars.

B) They generally have significant bulge populations.

C) They were more common when the universe was younger.

D) They have reddish colors.

E) They have well defined spiral arms.

C) They were more common when the universe was younger.

Why are Cepheid variables important?

A) Cepheid variables are stars that vary in brightness because they harbor a black hole.

B) Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.

C) Cepheids are a type of young galaxy that helps us understand how galaxies form.

D) Cepheids are supermassive stars that are on the verge of becoming supernovae and therefore allow us to choose candidates to watch if we hope to observe a supernova in the near future.

B) Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.

What is a standard candle?

A) an object for which we are likely to know the true luminosity

B) an object for which we can easily measure the apparent brightness

C) a class of objects in astronomy that all have exactly the same luminosity

D) any star for which we know the exact apparent brightness

E) a long, tapered candle that lights easily

A) an object for which we are likely to know the true luminosity

Why is the Hyades Cluster important for building up a catalog of the true luminosities of main-sequence stars?

A) It is an extremely bright cluster.

B) It is close enough to us that the distance to the cluster stars can be found by stellar parallax.

C) It is an old globular cluster that has been around our galaxy for several billion years.

D) We have brightness measurements for the stars in the cluster over many decades, so we know how the stars vary in brightness.

E) It contains many Cepheid variables.

B) It is close enough to us that the distance to the cluster stars can be found by stellar parallax.

How did Edwin Hubble measure the distance to the Andromeda Galaxy?

A) He measured its parallax.

B) He used main-sequence fitting.

C) He applied the period-luminosity relation to Cepheid variables.

D) He deduced it from its redshift.

E) He used white dwarf supernovae.

C) He applied the period-luminosity relation to Cepheid variables.

How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the "spiral nebulae" were actually entire galaxies?

A) There are no Cepheids in the Milky Way, so his discovery proved that it had to be in another galaxy.

B) He measured the stellar parallax of the Cepheid in Andromeda, was able to determine the distance to it, and showed that it was far outside the Milky Way Galaxy.

C) He used main-sequence fitting to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.

D) From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.

E) Since a Cepheid is a type of luminous galaxy, when he found it in Andromeda he was able to prove that Andromeda was a separate galaxy from the Milky Way.

D) From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.

What two quantities did Edwin Hubble plot against each other to discover the expansion of the Universe?

A) velocity and distance

B) luminosity and distance

C) velocity and temperature

D) luminosity and temperature

E) age and distance

A) velocity and distance

What is Hubble’s law?

A) The longer the time period between peaks in brightness, the greater the luminosity of the Cepheid variable star.

B) The recession velocity of a galaxy is directly proportional to its distance from us.

C) The recession velocity of a galaxy is inversely proportional to its distance from us.

D) The faster a spiral galaxy’s rotation speed, the more luminous it is.

E) The faster a spiral galaxy’s rotation speed, the less luminous it is.

B) The recession velocity of a galaxy is directly proportional to its distance from us.

Which of the following is a consequence of Hubble’s Law?

A) the Big Bang

B) all galaxies are moving away from us equally fast

C) the more distant a galaxy is from us, the faster it moves away from us

D) the closer a galaxy is to us, the faster it moves away from us

E) more distant galaxies appear younger

C) the more distant a galaxy is from us, the faster it moves away from us

What is the primary practical difficulty that limits the use of Hubble’s law for measuring distances?

A) Redshifts of galaxies are difficult to measure.

B) The recession velocities of distant galaxies are so great that they are hard to measure.

C) We do not know Hubble’s constant very accurately yet.

D) Hubble’s law is only useful theoretically; it is difficult to use in practice.

E) The motion of Earth relative to the Milky Way is difficult to account for.

C) We do not know Hubble’s constant very accurately yet.

White-dwarf supernovae are good standard candles for distance measurements for all the following reasons except which?

A) All white-dwarf supernovae involve the explosion of stars of nearly the same mass.

B) White-dwarf supernovae are so bright that they can be detected even in very distant galaxies.

C) White-dwarf supernovae are common enough that we detect several every year.

D) White-dwarf supernovae occur only among young and extremely bright stars.

E) All white-dwarf supernovae have similar light curves, which makes them easy to distinguish from massive-star supernovae.

D) White-dwarf supernovae occur only among young and extremely bright stars.

What makes white-dwarf supernovae good standard candles?

A) They are very bright, so they can be used to determine the distances to galaxies billions of light-years away.

B) They should all have approximately the same luminosity.

C) They occur so frequently that we can use them to measure the distances to virtually all galaxies.

D) We have had several occur close to us in the Milky Way, so we have been able to determine their luminosities very accurately.

E) both A and B

E) both A and B

What is the Tully-Fisher relation?

A) The longer the period of a galaxy’s variable stars, the more luminous it is.

B) The faster a spiral galaxy’s rotation speed, the more luminous it is.

C) The smaller a galaxy appears, the further away it is.

D) The redder a galaxy’s color, the further away it is.

E) The further away a galaxy is, the faster its recession velocity.

B) The faster a spiral galaxy’s rotation speed, the more luminous it is.

What is the most accurate way to determine the distance to a nearby star?

A) radar ranging

B) stellar parallax

C) main-sequence fitting

D) using Cepheid variables

E) Hubble’s law

B) stellar parallax

What is the most accurate way to determine the distance to a nearby galaxy?

A) radar ranging

B) stellar parallax

C) using Cepheid variables

D) the Tully-Fisher relation

E) Hubble’s law

C) using Cepheid variables

What is the most accurate way to determine the distance to a very distant irregular galaxy?

A) main-sequence fitting

B) using Cepheid variables

C) using a white-dwarf supernova as a standard candle

D) the Tully-Fisher relation

E) Hubble’s law

C) using a white-dwarf supernova as a standard candle

Which of the following sequences lists the methods for determining distance in the correct order from nearest to farthest?

A) main-sequence fitting, parallax, Cepheid variables, Tully-Fisher relation, Hubble’s law

B) parallax, main-sequence fitting, Cepheid variables, Tully-Fisher relation, Hubble’s law

C) parallax, main-sequence fitting, Tully-Fisher relation, Cepheid variables, Hubble’s law

D) parallax, main-sequence fitting, Tully-Fisher relation, white-dwarf supernovae, Hubble’s law

E) main-sequence fitting, parallax, Hubble’s law, Tully-Fisher relation, white-dwarf supernovae

B) parallax, main-sequence fitting, Cepheid variables, Tully-Fisher relation, Hubble’s law

What do scientists mean by the critical density of the universe?

A) the minimum density that a universe needs in order to form galaxies

B) the precise density marking the dividing line between a universe that has enough mass to contract again and a universe that will continue to expand forever

C) the minimum density that a universe needs in order to form stars

D) the average density of the space between galaxies

E) the minimum density that a universe needs in order to create hydrogen

B) the precise density marking the dividing line between a universe that has enough mass to contract again and a universe that will continue to expand forever

Dr. X believes that the Hubble constant is H0 = 55 km/s/Mpc. Dr. Y believes it is H0 = 80 km/s/Mpc. Which statement below automatically follows?

A) Dr. X believes that the universe is expanding, but Dr. Y does not.

B) Dr. X believes that the Andromeda Galaxy (a member of our Local Group) is moving away from us at a slower speed than Dr. Y believes.

C) Dr. X believes that the universe is older than Dr. Y believes.

D) Dr. X believes that the universe will someday stop expanding, while Dr. Y believes it will expand forever.

E) Dr. X believes that the universe has a much higher density than Dr. Y believes.

C) Dr. X believes that the universe is older than Dr. Y believes.

Dr. Smith believes that the Hubble constant is H0 = 70 km/s/Mpc. Dr. Jones believes it is H0 = 50 km/s/Mpc. Which statement below automatically follows?

A) Dr. Smith believes that the universe is expanding, but Dr. Jones does not.

B) Dr. Smith believes that the Andromeda Galaxy (a member of our Local Group) is moving away from us at a faster speed than Dr. Jones believes.

C) Dr. Smith believes that the universe is older than Dr. Jones believes.

D) Dr. Smith believes that the universe is younger than Dr. Jones believes.

E) Dr. Smith believes that the universe will someday stop expanding, while Dr. Jones believes it will expand forever.

D) Dr. Smith believes that the universe is younger than Dr. Jones believes.

Recall that Hubble’s law is written v = H0d, where v is the recession velocity of a galaxy located a distance d away from us, and H0 is Hubble’s constant. Suppose H0 = 65 km/s/Mpc. How fast would a galaxy located 500 megaparsecs distant be receding from us?

A) 65 km/s

B) 65 Mpc/s

C) 32,500 km/s

D) 9 km/s

E) 0.65 times the speed of light

C) 32,500 km/s

Hubble’s "constant" is constant in

A) time.

B) space.

C) space and time.

D) our Galaxy but different in others.

B) space.

Based on current estimates of the value of Hubble’s constant, how old is the universe?

A) between 4 and 6 billion years old

B) between 8 and 12 billion years old

C) between 12 and 16 billion years old

D) between 16 and 20 billion years old

E) between 20 and 40 billion years old

C) between 12 and 16 billion years old

Why can’t we see past the cosmological horizon?

A) The universe extends only to this horizon.

B) Beyond the cosmological horizon, we are looking back to a time before the universe had formed.

C) We do not have telescopes big enough.

D) We do not have sensitive enough detectors.

E) The cosmological horizon is infinitely far away, and we can’t see to infinity.

B) Beyond the cosmological horizon, we are looking back to a time before the universe had formed.

Does Hubble’s law work well for galaxies in the Local Group? Why or why not?

No, because galaxies in the Local Group are gravitationally bound together.

Cosmological redshift is the result of ___________.

the expansion of the universe

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