Deck 21: Galaxy Evolution

Question 1

What is a central dominant galaxy?

A)a galaxy around which many other smaller galaxies orbit
B)a giant spiral galaxy that exerts large tidal forces on other nearby galaxies
C)a spiral galaxy from which many smaller galaxies form when it is stripped apart by tidal forces
D)a giant elliptical galaxy at the center of a dense cluster
E)a hypothesized galaxy type that no longer exists but once dominated the structure of the universe

Answer 1

D

Question 2

Which of the following processes slowed the collapse of protogalactic clouds?

A)the formation of the first generation of stars
B)the conversion of gravitational potential energy into kinetic and thermal energy as the cloud collapsed
C)the shock waves from the exploding supernovae of the earliest stars
D)the pull of gravity of the mass of the cloud material
E)the radiating away of thermal energy

Answer 2

C

Question 3

How do observations of distant galaxies help us learn about galaxy evolution?

A)Observations at different distances show galaxies of different ages and therefore different stages of evolution.
B)We can observe the birth of galaxies.
C)We can observe the evolution of a single galaxy over time.
D)We can observe two galaxies merging and what the result is,helping us learn how mergers affect evolution.
E)We can see what our galaxy used to look like and therefore theorize about the physical processes that led to its current appearance.

Answer 3

A

Question 4

What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?

A)observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies
B)the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies
C)observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy
D)observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies
E)all of the above

Question 5

In the 1960s,Maarten Schmidt determined that quasars were very distant objects by

A)determining how luminous they were.
B)determining how small the source of light was from its variations in luminosity.
C)discovering that they were embedded in distant galaxies.
D)determining their redshifts.
E)determining their parallax angles.

Question 6

Why should galaxy collisions have been more common in the past than they are today?

A)Galaxies were more active in the past and therefore would have collided with each other more frequently.
B)Galaxies were much bigger in the past since they had not contracted completely.
C)Galaxies were closer together in the past because the universe was smaller.
D)Galaxies attracted each other more strongly in the past because they were more massive;they had not yet turned most of their mass into stars and light.
E)Galaxy collisions shouldn't have been more common in the past than they are now.

Question 7

Why do we believe that starburst galaxies represent a temporary stage in galaxy evolution?

A)We observe starbursts to last only a few years at a time.
B)Such galaxies produce so much light that they would have consumed all their gas long ago if they had always been forming stars at this high rate.
C)We don't see any nearby starburst galaxies.
D)All starburst galaxies look like normal spiral galaxies,aside from the starbursts.

Question 8

Why are telescopes sometimes called "time machines"?

A)because the author,H.G.Wells,used the term to describe telescopes in a book
B)because some of the oldest telescopes are still in use today
C)because observations of distant objects reveal them as they were in the past
D)because astronomers can use telescopes to see the Milky Way as it was when it was much younger
E)It's a journalistic misnomer: you cannot travel into the past or the future.

Question 9

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

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

Question 10

What evidence supports the theory that elliptical galaxies come from denser clouds?

A)Elliptical galaxies are denser than spiral galaxies.
B)Elliptical galaxies are generally larger than spiral galaxies.
C)Elliptical galaxies at high redshifts lack young,blue stars.
D)Elliptical galaxies have more gas than spiral galaxies.
E)Elliptical galaxies have denser stars than spiral galaxies.

Question 11

If we represent the Milky Way Galaxy as the size of a grapefruit (10-cm diameter),the distance to the Andromeda Galaxy would be about

A)10 cm.
B)3 m.
C)30 m.
D)1 km.
E)100 km.

Question 12

Starburst galaxies produce most of their light in the wavelength range of

A)X-rays.
B)the ultraviolet.
C)the visible.
D)the infrared.
E)all wavelengths.

Question 13

Why is a dense cloud more likely to produce an elliptical galaxy than a spiral galaxy?

A)The higher density of gas has a stronger force of gravity,and therefore the cloud collapses more quickly.
B)The force of gravity can pull the material into a more spherical shape.
C)The more frequent collisions between particles randomize the particle orbits.
D)The thickness of the dense cloud prevents a disk from forming.
E)The higher gas density forms stars more efficiently,so all the gas is converted into stars before a disk can form.

Question 14

I observe a galaxy that is 100 million light-years away: what do I see?

A)the light from the galaxy as it is today,but it is blueshifted
B)the light from the galaxy as it is today,but it is redshifted
C)the light from the galaxy as it was 100 million years ago and it it blueshifted
D)the light from the galaxy as it was 100 million years ago and it is redshifted
E)Nothing: the galaxy lies beyond the cosmological horizon.

Question 15

How many more stars does a starburst galaxy form,in one year,than the Milky Way?

A)a few
B)about ten
C)about a hundred
D)about a thousand
E)about the same,but it does so for much longer

Question 16

What evidence suggests that small galaxies in our Local Group have undergone two or more starbursts in the past?

A)We observe several small galaxies currently undergoing massive star formation.
B)We see small galaxies in which many stars have one age and many others have another age that is billions of years older.
C)We see evidence that small galaxies in our Local Group have experienced several collisions in the past.
D)We see evidence that several small galaxies were shot out of larger galaxies in our Local Group during an age of starburst activity.
E)We do not have any evidence that galaxies in our Local Group were once starburst galaxies.

Question 17

Which of the following is not true of quasars?

A)Some quasars are more than a thousand times more luminous than the Milky Way.
B)Quasars were more common in the past.
C)Quasars are powered by the energy radiated by matter falling into a central black hole.
D)Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time.
E)Some quasars can change their brightness every few hours.

Question 18

What is a quasar?

A)a starlike object that actually represents a bright patch of gas in the Milky Way
B)a very large galaxy thought to be formed by the merger of several smaller galaxies,typically found in the center of a galaxy cluster
C)a specialized astronomical instrument for observing distant stars
D)the extremely bright center of a distant galaxy,thought to be powered by a supermassive black hole
E)another name for very bright stars of spectral type O

Question 19

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

A)The beginning of the universe is modeled after a supernova explosion,and all the elements were produced in the proper quantities by the star.
B)Hydrogen and helium filled all of space,and certain regions of the universe were slightly denser than others.
C)Hydrogen and helium filled all of space,and all the universe was exactly the same density.
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 20

Which of the following is not a strong argument for the theory that some large elliptical galaxies formed as the result of galaxy collisions?

A)Elliptical galaxies dominate the population in dense galaxy clusters.
B)Some ellipticals have stars and gas that rotate opposite to the rest of the galaxy.
C)Some elliptical galaxies are surrounded by shells of stars.
D)Computer simulations predict that the product of a galaxy collision is generally an elliptical galaxy.
E)Galaxy collisions are common and most galaxies in the universe are elliptical.

Question 21

A protogalactic cloud with very little angular momentum is more likely to form an elliptical galaxy than a spiral galaxy.

Question 22

Galaxy mergers take hundreds of millions of years to complete.

Question 23

What are the typical features seen in quasar absorption lines of intergalactic clouds?

A)The hydrogen line is wider and lines from heavy elements are weaker at higher redshifts.
B)The hydrogen line is narrower and lines from heavy elements are weaker at higher redshifts.
C)The hydrogen line is wider and lines from heavy elements are stronger at higher redshifts.
D)The hydrogen line is narrower and lines from heavy elements are stronger at higher redshifts.
E)A few weak absorption lines are always seen at higher redshift than the quasar.

Question 24

The most active galactic nuclei are usually found at large distances from us;relatively few nearby galaxies have active galactic nuclei.What does this imply?

A)Supermassive black holes existed only when the universe was young and no longer exist today.
B)Active galactic nuclei tend to become less active as they age.
C)Active galactic nuclei can form only at large distances from the Milky Way.
D)The jets seen in many active galactic nuclei must cause them to move far away from us.

Question 25

How do we know that there are intergalactic clouds between a distant quasar and us?

A)We see hydrogen emission lines at redshifts smaller than that of the quasar.
B)We see hydrogen absorption lines at redshifts smaller than that of the quasar.
C)We see hydrogen emission lines at redshifts greater than that of the quasar.
D)We see hydrogen absorption lines at redshifts greater than that of the quasar.
E)We see that the emission lines from the quasar are lessened by intervening gas and dust.

Question 26

Which of the following types of protogalactic clouds is most likely to form a spiral galaxy?

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

Question 27

All of the following are true.Which of these gives evidence that quasars were more common in the early stages of the universe?

A)They are more common at very great distances.
B)They are very bright.
C)They are active galactic nuclei.
D)We don't see them in every galaxy.

Question 28

Which of the following is not a piece of evidence supporting the conclusion that active galactic nuclei are powered by accretion disks around supermassive black holes?

A)Observed radiation from the galactic center varies significantly in brightness in times as short as a few days.
B)Infrared observations show that many stars are forming near the centers of active galaxies.
C)Radio observations sometimes show long jets of material extending millions of light-years out from the galactic center.
D)The total amount of radiation coming from the galactic center is,in some cases,comparable to the amount of radiation put out by 10 billion or more ordinary stars.
E)Spectral lines from the galactic center indicate that clouds of gas are orbiting a central object at very high speed.

Question 29

Which of the following is evidence for supermassive black holes in active galaxies?

A)the discovery of powerful jets coming from a compact core
B)rapid changes in the luminosity of the galaxy nucleus
C)quasars emit approximately equal power at all wavelengths from infrared to gamma rays
D)very high speed orbital motions around galactic nuclei
E)all of the above

Question 30

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

A)The X-ray source is a quasar.
B)The X-ray source contains a black hole with an accretion disk.
C)The X-ray source is no more than a few light-days in diameter.
D)The X-ray source must have a strong,rapidly varying magnetic field.
E)We are seeing the rapid orbit of two stars in a binary system.

Question 31

Galaxy collisions were more common in the past.

Question 32

Where are the X-rays produced that are emitted by quasars and other active galactic nuclei?

A)in hot gas in an accretion disk around a central black hole
B)in ionization nebulae of interstellar gas that surround the accretion disk
C)in dust grains in molecular clouds that encircle the active galactic nucleus
D)in fast-moving electrons that jet from the active galactic nucleus
E)all of the above

Question 33

The collision of two spiral galaxies will likely result in a single giant spiral galaxy.

Question 34

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

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

Question 35

If an object doubles its luminosity in 10 hours,how large can the emitting source of light be?

A)about 10 light-years across
B)about 10 parsecs across
C)about 10 light-hours across
D)varies depending on how luminous the object is
E)varies depending on how far away the object is

Question 36

How is the energy that powers radio galaxies,quasars,and other active galactic nuclei produced?

A)by nuclear fusion near a central black hole
B)by magnetic fields that trap and accelerate charged particles,which then radiate high amounts of energy
C)by matter that has been converted to pure energy being shot out as jets by a central black hole
D)by gravity,which converts potential energy of matter falling toward a central black hole into kinetic energy,which is then converted to thermal energy by collisions among the particles of matter
E)by matter-antimatter annihilation near a central black hole

Question 37

Galaxies at very large distances from the Milky Way often look distorted.

Question 38

What is a galactic wind?

A)a jet of ionized particles shot out of a starburst galaxy
B)hot gas erupting into intergalactic space from a large superbubble
C)the heat (infrared radiation)emitted by dust grains in the large molecular clouds of starburst galaxies
D)the cooler gas pushed out of a starburst galaxy by the intense radiation pressure
E)a wind created by the expansion of the universe that can move galaxies around

Question 39

Some galaxies in the Local Group stopped forming stars for several billion years but then started again.

Question 40

A protogalactic cloud with slow star formation is more likely to form a spiral galaxy than an elliptical galaxy.

Question 41

According to observations,what type of galaxy was much more common when the universe was 2 billion years old?

A)elliptical galaxies
B)spiral galaxies
C)irregular galaxies
D)We can't say,because we are living at a time when the universe is 14 billion years old,not 2 billion years.

Question 42

How do jets produced by radio galaxies differ from those of protostars?

Question 43

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

Question 44

How does a starburst end? What might happen to the galaxy afterwards?

Question 45

Quasars radiate most of their energy as radio emission.

Question 46

Why do spiral galaxy mergers often trigger starbursts?

Question 47

Briefly explain how we think quasars produce so much energy.

Question 48

Explain why galaxy interactions are far more common than star-star interactions.

Question 49

Observations of quasar absorption lines show that intergalactic clouds were more common in the past.

Question 50

Process of Science: Explain how we can use telescopes as time machines to directly test theories of galaxy formation.

Question 51

Telescopes being planned for the study of the earliest stages in galactic lives will be optimized for observations in

A)visible light.
B)infrared light.
C)radio waves.
D)X-rays.

Question 52

Collisions between galaxies typically unfold over a period of

A)several days.
B)several months.
C)thousands of years.
D)hundreds of millions of years.

Question 53

Briefly explain why starburst galaxies appear fairly ordinary when they are observed in visible light but extraordinary when they are observed in infrared light.

Question 54

Give examples demonstrating the role of "nature" and "nurture" in galaxy evolution.

Question 55

Process of Science: In the discovery of quasars,the radio source 3C273 was found to have strong emission lines at wavelengths that did not correspond to any known element on Earth.Suppose a scientist postulated that they had discovered a new element that only existed in these powerful radio sources.How would you test this?

Question 56

Which of the following is an important starting assumption in models of galaxy formation?

A)Galaxies form first,then black holes.
B)All galaxies start out as spiral galaxies.
C)Black holes form first,seeding the formation of galaxies.
D)Some regions in the universe start out denser than others.

Question 57

How are the jets produced by radio galaxies similar to those from protostars?

Question 58

Starburst galaxies produce most of their light in the infrared.

Question 59

What information about protogalactic gas clouds is contained in quasar absorption lines?

Question 60

Process of Science: What evidence do scientists have that supermassive black holes exist?

Question 61

13)According to the theory that active galactic nuclei are powered by supermassive black holes,the high luminosity of an active galactic nucleus primarily consists of

A)light emitted by hot gas in an accretion disk that swirls around the black hole.
B)intense radiation emitted by the black hole itself.
C)the combined light of thousands of young,high-mass stars that orbit the black hole.
D)radio waves emitted from radio lobes found on either side of the galaxy we see in visible light.

Question 62

Hubble Space Telescope observations have shown that when the mass of the central black hole is very large,then

A)the mass of the halo and disk of the host galaxy is also very large.
B)the host galaxy is eventually completely consumed by the black hole.
C)the galaxy is always a spiral galaxy.
D)the mass of the bulge of the host galaxy is also very large.

Question 63

The distinguishing feature of a starburst galaxy is

A)the presence of an unusually large number of binary star systems containing X-ray bursters.
B)a very large luminosity compared to the total luminosity of the Milky Way.
C)strong radio emission from "lobes" of material well outside the visible boundaries of the galaxy.
D)a rate of star formation that may be 100 or more times greater than that in the Milky Way.

Question 64

If the Andromeda Galaxy collided with the Milky Way,what would most likely happen to Earth?

A)The Sun and all its planets would be crushed by collisions with stars and planets from the Andromeda Galaxy.
B)Nothing.
C)The Sun would not be disturbed,but the solar system would be ripped apart.
D)The Sun will turn into a red giant and explode.

Question 65

Which of the following features is not a feature of central dominant galaxies?

A)They're found in clusters of galaxies.
B)They are often spiral galaxies.
C)They often have multiple galactic nuclei near their centers.
D)They are thought to form by the merger of several smaller galaxies.

Question 66

According to current understanding,what is a quasar?

A)an active galactic nucleus that is particularly bright
B)a very large galaxy thought to be formed by the merger of several smaller galaxies,typically found in the center of a galaxy cluster
C)any object with an extremely large redshift is called a quasar
D)a galaxy with an unusually high rate of star formation

Question 67

The best evidence for the existence of supermassive black holes is

A)very high orbital velocities in a very compact region.
B)evidence for jet velocities that approach the speed of light.
C)large quantities of high-energy emission such as X-rays and gamma rays,and radio emission from relativistic electrons.
D)huge dark regions in the centers of galaxies,where black holes have been sucking in the galaxy from the inside out.

Question 68

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

Question 69

Interactions among galaxies also are thought to influence a galaxy's type in at least some cases.Which of the following does not support the idea that interactions can shape galaxies?

A)the fact that more distant galaxies have larger redshifts
B)computer modeling of collisions between galaxies
C)the fact that galaxies with distorted appearances are more common at great distances than nearby
D)the presence of features such as "tails" extending out of galaxies,bridges between galaxies,and rings of stars around galaxies

Question 70

Which of the following statements is not an assumption used in models of galaxy formation?

A)The universe started out filled almost uniformly with hydrogen and helium.
B)Some regions in the universe were slightly more dense than others.
C)The universe is expanding.
D)Gas contracted to form the disks of galaxies before any stars were born.

Question 71

Which of the following phenomena are not thought to be results of collisions or other interactions between galaxies?

A)the presence of very large,central dominant galaxies in clusters of galaxies
B)the fact that elliptical galaxies are more common in clusters of galaxies than outside clusters
C)starbursts
D)the fact that spiral galaxies have both disk and halo components

Question 72

Which of the following phenomena is probably not related to the presence of a supermassive black hole?

A)quasars
B)the radio emission from radio galaxies
C)the huge jets seen emerging from the centers of some galaxies
D)the large sizes of central dominant galaxies

Question 73

Intergalactic hydrogen clouds are easiest to study by looking at

A)21 cm radio emission.
B)radio emission from molecular hydrogen.
C)X-ray emission.
D)absorption lines in quasar spectra.

Question 74

Why are collisions between galaxies more likely than collisions between stars within a galaxy?

A)Relative to their sizes,galaxies are closer together than stars.
B)Galaxies are much larger than stars.
C)Galaxies travel through space much faster than stars.
D)Galaxies have higher redshifts than stars.

Question 75

The unusually bright centers found in some galaxies are called

A)active galactic nuclei.
B)halos.
C)supermassive black holes.
D)starbursts.

Question 76

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

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

Question 77

Current understanding holds that a galaxy's type (spiral,elliptical,or irregular)

A)is always determined by the angular momentum of the protogalactic cloud that formed it.
B)may either be the result of conditions in the protogalactic cloud that formed it or the result of later interactions with other galaxies.
C)is determined by whether the galaxy is located in a cluster where collisions are likely or outside a cluster where collisions are less likely.
D)may either be a result of the mass of the protogalactic cloud that formed it or the result of the heavy element abundance in that cloud.

Question 78

We can study how galaxies evolve because

A)galaxies are transparent to visible light.
B)we are really smart astronomers.
C)we can watch as they interact in real time.
D)the farther away we look,the further back in time we see.

Question 79

Two ways in which the starting conditions in a protogalactic cloud might cause it to become an elliptical (rather than spiral)galaxy are if the cloud begins with either

A)relatively little angular momentum or relatively high density.
B)relatively high angular momentum or relatively low density.
C)relatively high mass and a relatively low abundance of heavy elements.
D)relatively low mass and a relatively high abundance of heavy elements.

Question 80

The mass of a supermassive black hole thought to power a typical bright active galactic nucleus is roughly

A)3 solar masses.
B)10 solar masses.
C)1 trillion solar masses.
D)1 billion solar masses.