Question 1

List at least three qualities that make an astronomical object a good standard candle.

Accepted Answer

All standard candles must have some observable property that allows us to recognize the object as a member of the unique class. For example, Cepheids vary in brightness in a characteristic way, allowing us to distinguish them from other stars; white dwarf supernova have a unique light- curve that allows us to distinguish them from massive star supernova. The remaining answers will vary, but some additional key properties include little statistical scatter in brightness; high luminosity so that they can be seen at a great distance; and relative commonness so that they can be found in many objects.

Question 2

Based on the number of galaxies visible in the Hubble Deep Field (Figure 16.1 in your textbook), the estimated number of galaxies in our observable universe is about .

Accepted Answer

A) Infinity 
B) 100 million 
C) 50,000 
D) 100 billion 
A) Infinity 
B) 100 million 
C) 50,000 
D) 100 billion D

Question 3

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

Accepted Answer

A) More distant galaxies appear younger. 
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 Big Bang 
E) The closer a galaxy is to us, the faster it moves away from us. 
A) More distant galaxies appear younger. 
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 Big Bang 
E) The closer a galaxy is to us, the faster it moves away from us. C

Question 4

Which of the following cannot be true of the very first stars formed in the universe?

Accepted Answer

A) Some may have formed in large clusters. 
B) Some may have had rocky planets around them. 
C) Some may still exist in the Milky Way today. 
D) Some may have all exploded as supernovae by now. 
E) Some may have formed singly, in isolation from one another. 
A) Some may have formed in large clusters. 
B) Some may have had rocky planets around them. 
C) Some may still exist in the Milky Way today. 
D) Some may have all exploded as supernovae by now. 
E) Some may have formed singly, in isolation from one another.

Question 5

Which of the following gives the two main assumptions of theoretical models of galaxy evolution?

Accepted Answer

A) Hydrogen and helium filled all of space, and certain regions of the universe were slightly denser than others. 
B) The beginning of the universe is modeled after a supernova explosion, and all elements were produced by this exploding star. 
C) Hydrogen and helium filled all of space, and the entire universe had exactly the same density everywhere. 
D) The universe has always been expanding, and denser areas contracted to form the first stars. 
E) The universe was composed originally only of hydrogen, and all the other elements came from stars. 
A) Hydrogen and helium filled all of space, and certain regions of the universe were slightly denser than others. 
B) The beginning of the universe is modeled after a supernova explosion, and all elements were produced by this exploding star. 
C) Hydrogen and helium filled all of space, and the entire universe had exactly the same density everywhere. 
D) The universe has always been expanding, and denser areas contracted to form the first stars. 
E) The universe was composed originally only of hydrogen, and all the other elements came from stars.

Question 6

Why do elliptical galaxies appear yellow or red?

Accepted Answer

A) They contain no hot, young blue stars 
B) They contain only massive- stars that have progressed to the red- giant stage 
C) They have very little dust or cool gas, and thus have little ongoing star formation 
D) A and B 
E) A and C 
A) They contain no hot, young blue stars 
B) They contain only massive- stars that have progressed to the red- giant stage 
C) They have very little dust or cool gas, and thus have little ongoing star formation 
D) A and B 
E) A and C

Question 7

Why can't we see past the cosmological horizon?

Accepted Answer

A) Beyond the cosmological horizon, we are looking back to a time before the universe had formed. 
B) We do not have detectors sensitive enough. 
C) We do not have telescopes big enough. 
D) The cosmological horizon is infinitely far away, and we can't see to infinity. 
E) The universe extends only to this horizon. 
A) Beyond the cosmological horizon, we are looking back to a time before the universe had formed. 
B) We do not have detectors sensitive enough. 
C) We do not have telescopes big enough. 
D) The cosmological horizon is infinitely far away, and we can't see to infinity. 
E) The universe extends only to this horizon.

Question 8

Ming measures a recession velocity of 2000 km/sec for a galaxy. About how far away is that galaxy if the Hubble constant is 20 km/sec/million light years? (Hint: be sure to check the units in your calculation.)

Accepted Answer

A) 40 thousand light years 
B) 40 billion light years 
C) 100 million light years 
D) 100 light years 
A) 40 thousand light years 
B) 40 billion light years 
C) 100 million light years 
D) 100 light years

Question 9

Suppose we observe a source of X- rays that varies substantially in brightness over a period of a few days. What can we conclude?

Accepted Answer

A) The X- ray source must have a strong, rapidly varying magnetic field. 
B) The X- ray source is a quasar. 
C) The X- ray source contains a black hole with an accretion disk. 
D) The X- ray source is no more than a few light- days in diameter. 
A) The X- ray source must have a strong, rapidly varying magnetic field. 
B) The X- ray source is a quasar. 
C) The X- ray source contains a black hole with an accretion disk. 
D) The X- ray source is no more than a few light- days in diameter.

Question 10

Which of the following is not true of quasars?

Accepted Answer

A) The light produced by quasars comes from an accretion disk surrounding a supermassive black hole. 
B) Quasars were more common in the past. 
C) Some quasars are more than a thousand times more luminous than the Milky Way. 
D) Some quasars can change their brightness on the timescale of hours. 
E) Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time. 
A) The light produced by quasars comes from an accretion disk surrounding a supermassive black hole. 
B) Quasars were more common in the past. 
C) Some quasars are more than a thousand times more luminous than the Milky Way. 
D) Some quasars can change their brightness on the timescale of hours. 
E) Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time.

Question 11

In a uniformly expanding universe, which statement best describes the situation as viewed from an observer in Galaxy C (not the Milky Way Galaxy)?

Accepted Answer

A) Galaxy C observer sees some galaxies moving away, some moving towards itself. 
B) Galaxy C observer sees all galaxies moving away from the Milky Way Galaxy. 
C) Galaxy C observer sees all other galaxies moving away from itself. 
A) Galaxy C observer sees some galaxies moving away, some moving towards itself. 
B) Galaxy C observer sees all galaxies moving away from the Milky Way Galaxy. 
C) Galaxy C observer sees all other galaxies moving away from itself.

Question 12

All of the following observations are real. Which one does not support the theory that active galactic nuclei are powered by accretion disks around massive black holes?

Accepted Answer

A) The most luminous active galactic nuclei have huge redshifts. 
B) Spectra of active galactic nuclei show that clouds of gas are orbiting a central object at very high speed. 
C) X- ray emission from active galactic nuclei can vary significantly in times as short as a few days. 
D) The total luminosity of an active galactic nucleus can be as high as about 10 billion times that of the Sun. 
A) The most luminous active galactic nuclei have huge redshifts. 
B) Spectra of active galactic nuclei show that clouds of gas are orbiting a central object at very high speed. 
C) X- ray emission from active galactic nuclei can vary significantly in times as short as a few days. 
D) The total luminosity of an active galactic nucleus can be as high as about 10 billion times that of the Sun.

Question 13

This figure shows the Cepheid period- luminosity relation. A Cepheid star with a period of 30 days has the same apparent brightness as a nearby G2 star. How many times further away is the Cepheid star?

Accepted Answer

A) The Cepheid star is 100 times further away than the nearby G2 star. 
B) The Cepheid star is 10,000 times further away than the nearby G2 star. 
C) The Cepheid star is 10 times further away than the nearby G2 star. 
D) The Cepheid star is actually a factor of 10 times closer than the nearby G2 star. 
A) The Cepheid star is 100 times further away than the nearby G2 star. 
B) The Cepheid star is 10,000 times further away than the nearby G2 star. 
C) The Cepheid star is 10 times further away than the nearby G2 star. 
D) The Cepheid star is actually a factor of 10 times closer than the nearby G2 star.

Question 14

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

Accepted Answer

A) ellipticals 
B) irregulars 
C) lenticulars 
D) spirals 
A) ellipticals 
B) irregulars 
C) lenticulars 
D) spirals

Question 15

According to the theory that active galactic nuclei are powered by supermassive black holes, the energy released as light comes from .

Accepted Answer

A) gravitational potential energy released by matter that is falling toward the black hole 
B) jets emerging from the accretion disk 
C) nuclear fusion in the accretion disk surrounding the black hole 
D) matter- antimatter annihilation occurring just outside the event horizon of the black hole 
A) gravitational potential energy released by matter that is falling toward the black hole 
B) jets emerging from the accretion disk 
C) nuclear fusion in the accretion disk surrounding the black hole 
D) matter- antimatter annihilation occurring just outside the event horizon of the black hole

Question 16

Give several observations supporting the idea that the high redshifts of quasars really do imply great distances.

Accepted Answer

(a)We see many quasars with high redshif

Question 17

What two quantities did Edwin Hubble compare for a sample of galaxies to discover the expansion of the universe?

Accepted Answer

A) velocity and temperature 
B) luminosity and distance 
C) velocity and distance 
D) age and distance 
E) luminosity and temperature 
A) velocity and temperature 
B) luminosity and distance 
C) velocity and distance 
D) age and distance 
E) luminosity and temperature

Question 18

Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy?

Accepted Answer

A) a very massive cloud with any density and a lot of angular momentum 
B) a dense cloud with quite a bit of angular momentum 
C) a low- density cloud with quite a bit of angular momentum 
D) a dense cloud with very little angular momentum 
E) a very low- density cloud with very little angular momentum 
A) a very massive cloud with any density and a lot of angular momentum 
B) a dense cloud with quite a bit of angular momentum 
C) a low- density cloud with quite a bit of angular momentum 
D) a dense cloud with very little angular momentum 
E) a very low- density cloud with very little angular momentum

Question 19

The observed relationship between the masses of central black holes and the bulge masses of galaxies implies that .

Accepted Answer

A) quasars were more common 10 billion years ago than they are today 
B) the black hole will eventually suck in the rest of the galaxy 
C) galaxy formation and supermassive black hole formation must be related somehow 
D) the biggest galaxies have the most luminous quasars 
A) quasars were more common 10 billion years ago than they are today 
B) the black hole will eventually suck in the rest of the galaxy 
C) galaxy formation and supermassive black hole formation must be related somehow 
D) the biggest galaxies have the most luminous quasars

Question 20

One possible explanation for a galaxy's type invokes the angular momentum of the protogalactic cloud from which it formed. Suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum. Assuming its type has not changed due to other interactions, we'd expect this galaxy to be .

Accepted Answer

A) a torn and incoherent galaxy 
B) a spiral galaxy 
C) an elliptical galaxy 
D) an irregular galaxy 
A) a torn and incoherent galaxy 
B) a spiral galaxy 
C) an elliptical galaxy 
D) an irregular galaxy

List at least three qualities that make an astronomical object a good standard candle.

Based on the number of galaxies visible in the Hubble Deep Field (Figure 16.1 in your textbook), the estimated number of galaxies in our observable universe is about .

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

Which of the following cannot be true of the very first stars formed in the universe?

Which of the following gives the two main assumptions of theoretical models of galaxy evolution?

Why do elliptical galaxies appear yellow or red?

Why can't we see past the cosmological horizon?

Ming measures a recession velocity of 2000 km/sec for a galaxy. About how far away is that galaxy if the Hubble constant is 20 km/sec/million light years? (Hint: be sure to check the units in your calculation.)

Suppose we observe a source of X- rays that varies substantially in brightness over a period of a few days. What can we conclude?

Which of the following is not true of quasars?

In a uniformly expanding universe, which statement best describes the situation as viewed from an observer in Galaxy C (not the Milky Way Galaxy)?

All of the following observations are real. Which one does not support the theory that active galactic nuclei are powered by accretion disks around massive black holes?

This figure shows the Cepheid period- luminosity relation. A Cepheid star with a period of 30 days has the same apparent brightness as a nearby G2 star. How many times further away is the Cepheid star?

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

According to the theory that active galactic nuclei are powered by supermassive black holes, the energy released as light comes from .

Give several observations supporting the idea that the high redshifts of quasars really do imply great distances.

What two quantities did Edwin Hubble compare for a sample of galaxies to discover the expansion of the universe?

Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy?

The observed relationship between the masses of central black holes and the bulge masses of galaxies implies that .

One possible explanation for a galaxy's type invokes the angular momentum of the protogalactic cloud from which it formed. Suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum. Assuming its type has not changed due to other interactions, we'd expect this galaxy to be .

A Modern View of the Universe

Discovering the Universe for Yourself

The Science of Astronomy

Making Sense of the Universe: Understanding Motion, Energy, and Gravity

Light: the Cosmic Messenger

Formation of the Solar System

Earth and the Terrestrial Worlds

Jovian Planet System

Asteroids, Comets, and Dwarf Planets: Their Nature, Orbits, and Impacts

Other Planetary Systems: the New Science of Distant Worlds

Our Star

Surveying the Stars

Star Stuff

The Bizarre Stellar Graveyard

Our Galaxy

The Birth of the Universe

Dark Matter, Dark Energy, and the Fate of the Universe

Life in the Universe

Filters

Exam 16: A Universe of Galaxies

List at least three qualities that make an astronomical object a good standard candle.

Based on the number of galaxies visible in the Hubble Deep Field (Figure 16.1 in your textbook), the estimated number of galaxies in our observable universe is about .

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

Which of the following cannot be true of the very first stars formed in the universe?

Which of the following gives the two main assumptions of theoretical models of galaxy evolution?

Why do elliptical galaxies appear yellow or red?

Why can't we see past the cosmological horizon?

Ming measures a recession velocity of 2000 km/sec for a galaxy. About how far away is that galaxy if the Hubble constant is 20 km/sec/million light years? (Hint: be sure to check the units in your calculation.)

Suppose we observe a source of X- rays that varies substantially in brightness over a period of a few days. What can we conclude?

Which of the following is not true of quasars?

In a uniformly expanding universe, which statement best describes the situation as viewed from an observer in Galaxy C (not the Milky Way Galaxy)?

All of the following observations are real. Which one does not support the theory that active galactic nuclei are powered by accretion disks around massive black holes?

This figure shows the Cepheid period- luminosity relation. A Cepheid star with a period of 30 days has the same apparent brightness as a nearby G2 star. How many times further away is the Cepheid star?

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

According to the theory that active galactic nuclei are powered by supermassive black holes, the energy released as light comes from .

Give several observations supporting the idea that the high redshifts of quasars really do imply great distances.

What two quantities did Edwin Hubble compare for a sample of galaxies to discover the expansion of the universe?

Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy?

The observed relationship between the masses of central black holes and the bulge masses of galaxies implies that .

One possible explanation for a galaxy's type invokes the angular momentum of the protogalactic cloud from which it formed. Suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum. Assuming its type has not changed due to other interactions, we'd expect this galaxy to be .

A Modern View of the Universe

Discovering the Universe for Yourself

The Science of Astronomy

Making Sense of the Universe: Understanding Motion, Energy, and Gravity

Light: the Cosmic Messenger

Formation of the Solar System

Earth and the Terrestrial Worlds

Jovian Planet System

Asteroids, Comets, and Dwarf Planets: Their Nature, Orbits, and Impacts

Other Planetary Systems: the New Science of Distant Worlds

Our Star

Surveying the Stars

Star Stuff

The Bizarre Stellar Graveyard

Our Galaxy

The Birth of the Universe

Dark Matter, Dark Energy, and the Fate of the Universe

Life in the Universe

Filters