Astro 4

The very strong source of radio waves at the center of our Galaxy is called

Sagittarius A

Which of the following objects is considered useful to astronomers as a "standard bulb" for determining distances?

a. type Ia supernovae

The astronomer who first solved the problem of the strange red-shifts seen in quasar spectra and thus helped us understand that the quasars must be distant objects was

b. Maarten Schmidt

The first astronomer to show that spiral nebulae (today called spiral galaxies) have large Doppler shifts was

b. Vesto Slipher

According to Hubble's Law, if two galaxies are not part of our Local Group, and galaxy B is three times farther away from us as Galaxy A, then Galaxy B will

c. move away from us three times faster than A

How do astronomers now explain the fact that the energy emitting regions for quasars are so small?

c. quasars are the result of matter falling into a black hole; the event horizons of even supermassive black holes are extremely small on the cosmic scale

Which of the following statements about the different types (shapes) of galaxies is correct?

collisions and mergers between galaxies can sometimes change a galaxy's type (shape)

When quasars "shine" (in visible light and other kinds of radiation) with a lot of energy, where (what location) does this huge amount of energy come from?

d. from an accretion disk around a supermassive black hole

An astronomer who loved reading the Guinness Book of World Records when she was a child becomes obsessed with quasars and wants desperately to find the most distant quasar ever (the one with the largest redshift.) Where should she be looking to have the best chance of finding such a quasar?

d. in or near a distant cluster of galaxies that can act like a gravitational lens

How are galaxies and quasars related?

d. quasars are active supermassive black holes at the centers of galaxies

Which of the following observations is a convincing argument for the idea that quasars are located inside galaxies?

d. relatively nearby quasars show "fuzz" around them with the same spectra and redshift as the quasar

The type of galaxy that consists almost entirely of old stars and is thus less blue (more yellow and reddish) than the other types is:

elliptical

What method would astronomers use to find the distance to a galaxy so far away that individual stars are impossible to make out (resolve)?

finding the redshift and using Hubble's Law

Where would you look for the youngest stars in the Milky Way Galaxy?

in the disk

Our Milky Way Galaxy is what type of galaxy?

spiral

A "galactic year" as defined by astronomers is:

the time it takes the Sun to revolve once around the center of the Milky Way Galaxy

Which of the following is NOT a characteristic of a spiral galaxy?

when we take spectra of its stars, they have far less of the heavier elements than the Sun

The scientist who made the first telescopic survey of the Milky Way and discovered that it is composed of a huge number of individual stars was

Galileo Galilei

Your weird cousin, who is really into astronomy, decides that the return address he uses on his letters is incomplete! To his city, state, and country, he begins to add: "North America, Earth, Solar System..." If he now wants to include the name of the Galaxy's spiral-structure feature in which the Earth is located, how should his address end?

Orion Spur

Which of the following statements about dark matter in the Galaxy is FALSE?

While the dark matter cannot be observed with our present-day instruments, we still have a pretty good idea what it consist of

Astronomers today know a lot about the size and shape of the Milky Way Galaxy. Which of the following common objects most resembles the shape of our Galaxy?

a CD or DVD

About two thirds of the nearby spiral galaxies (which we can study in more detail) don't have a round central bulge, but instead show

a central bulge with a bar of stars in the middle

Objects orbiting around the center of the Milky Way obey Kepler's 3rd Law. This means that:

a cloud of gas or star that is further from the center will generally take more time to orbit

Astronomers making observations in our Galaxy have been able to rule out a number of suggestions for what the dark matter in the Galaxy might be. Which of the following have we NOT been able to rule out (which suggestion is still "in the running")?

a new kind of subatomic particle

The central region of our Galaxy is not as flat as its main disk of stars. Which of the following has roughly the same shape as our central region of stars?

a peanut

A Congressman from Texas visits our National Observatory in Tucson, Arizona, and wants to be shown an object in the universe with the "biggest darn redshift you ever saw". What type of object should the astronomers show him?

a quasar

You suddenly get an uncontrollable urge to find out more about the other side of the Milky Way Galaxy (the regions beyond the center). Where should you rush off to?

a radio telescope that can observe at 21-cm wavelengths

Galaxies that we see as they were 11 billion years ago or more, as compared to galaxies today, are generally:

a. bluer and smaller

The Tully-Fisher method for measuring the distance to galaxies relies on the observed relationship between the luminosity of a spiral galaxy and

a. its rotational velocity (as determined from the width of the 21-cm line)

Why do astronomers think that there are fewer quasars today than there were billions of years ago?

a. quasars are seen when the supermassive black hole at the center of a galaxy has a lot of "food to eat" (stars and gas) and the amount of available food tends to decrease with time

The Hubble Space Telescope has enabled astronomers to explore an active galaxy such as M87 in remarkable detail. Which of the following observations of M87 is NOT an important part of the web of evidence that shows it must have a supermassive black hole at the center?

a. the discovery of a gravitational lens in M87

How do astronomers explain the energetic jets that come out of quasars and active galactic nuclei in opposite directions?

a. the jets are "spit out" from the chaotic accretion disks of supermassive black holes in directions that are perpendicular to the disk

For galaxies that have super-massive black holes at their centers, how do astronomers find that the mass of the host galaxy and the mass of the black hole are related?

a. the more massive the galaxy, the more massive the central black hole

After several decades of observation, astronomers have concluded that quasars are

a. very powerful and compact sources of energy at the centers of distant galaxies

Astronomers now think that there is a black hole with more than 4 million times the mass of our Sun at the center of our Galaxy? Roughly how large would the event horizon of such a supermassive black hole be? a. the size of our Moon

about 17 times the size of the Sun

In the future, astronomers believe that the Milky Way Galaxy has additional collisions in store. Which of the following nearby galaxies are eventually going to collide with our own?

all of the above

The Population I stars in the Milky Way Galaxy

all of the above

Astronomers now know that surrounding the main body of our Galaxy (which our various kinds of telescopes have shown to us) and our fainter halo of stars there is

an invisible halo made of what astronomers are calling "dark matter"

An astronomer claims that the large redshifts of all quasars are caused by some new mechanism and not the expansion of the universe. The redshift tells us nothing, he says, about where any quasar is located. Which of the following would be a way to disprove his view of quasars?

b. find a number of cases where a quasar seen in a cluster of galaxies has the same redshift as all the galaxies in the cluster

If I want to find a sizeable collection of Population II stars in the Milky Way Galaxy, where would be a good place to look?

b. in a globular cluster high above the Galaxy's disk

There is some irony in the fact that the Hubble Space Telescope has shown that Edwin Hubble's classification scheme for galaxy shapes only works in the later stages of the universe. What have really deep pictures (going way back in time) taken with the Hubble Telescope shown about galaxies long ago (in the first few billion years after the Big Bang)?

b. long ago, galaxy shapes were not (for the most part) regular and organized; galaxies looks chaotic and lumpy

How can supermassive black holes at the centers of galaxies help new stars to form in that galaxy?

b. new stars can form when the flow of particles from a black hole accretion disk or jet compresses the material some distance away from the black hole and starts the "clumping" that leads to the formation of stars

What observation in astronomy, made AFTER the discovery of quasars, was a big help to astronomers in figuring out what quasars really were?

b. the discovery that the Milky Way Galaxy has a black hole at the center with enough mass for 4 million Suns

If a very distant galaxy looks blue overall to astronomers, from this they can conclude that:

b. the galaxy must have a lot of young stars and thus active star formation must still be going in it

Before you can use Hubble's Law to get the distance to a galaxy, what observation must you make of that galaxy?

b. you must take a spectrum of the galaxy and measure the red shift

Astronomers observe the Small Magellanic Cloud (SMC), a not very dense, rather small galaxy near us. They notice that even those stars that formed recently have relatively few heavier elements (when compared to such recent stars in our Milky Way.) What is the likely explanation for this deficiency?

because the SMC is small and its stars are widely spaced, the rate of star formation (and star death) is much slower there

One of the most important observations in the history of astronomy was the one by Edwin Hubble that established that there are other galaxies, quite removed from the Milky Way. How did Hubble show this?

by observing a Cepheid variable in a nearby galaxy and using it to get the distance

The astronomer who assisted Edwin Hubble at the Mount Wilson Observatory and helped him establish the expansion of the universe was:

c. Milton Humason

Why is the use of Hubble's Law to measure distances to galaxies so important to astronomers?

c. Most galaxies are so far away, the only way to get distances to them is to use Hubble's Law

Which is one reason that the typical galaxy's mass-to-light ratio (in units of the Sun's mass over the Sun's luminosity) generally greater than 1?

c. galaxies contain many more stars that shine much less brightly than the Sun

If a galaxy contains a great deal of "dark matter," what will that do the galaxy's mass-to-light ratio?

c. increase it quite a bit

Today, astronomers find compelling evidence that the energy source of the quasars and active galaxies is

c. matter falling toward a supermassive black hole at the center of a galaxy

What makes astronomers believe that the energy source in quasars is only a few light months across (the distance light travels in a few months)?

c. quasars show variations in their energy output that have a period of a few months

Today we know that what all quasars have in common is that they appear to be small sources of energy with

c. redshifts that indicate they are far away

Why do galaxies collide, while stars almost never do?

c. stars are much further apart (compared to how big they are) than galaxies are

An astronomer is observing a distant galaxy which looks blue. Which of the following can she conclude from this observation?

c. the galaxy must have a lot of star formation going on at the time we are seeing it

With enormous effort, a team of astronomers manages to collect enough light from a galaxy far, far away to produce a spectrum. That spectrum has lines from the elements carbon, silicon, and sulfur. This tells the team that

c. the galaxy must have had an entire generation of stars that was born, lived, and died

Astronomers have established that quasars and active galaxies have a lot of mass at their centers in a very small volume of space. Why can't this mass be in the form of a cluster of stars that are quite close to each other?

c. to fit as much matter into the cluster as we observe, the stars in the cluster must be so close to each other they would merge into a superstar and soon collapse into a black hole

What method would astronomers use to find the distance to a remote quasar? a. parallax

d. finding the redshift and using Hubble's Law

Which of the following statements about the implications of Hubble's Law is FALSE?

d. if you were observing the universe from a distant galaxy, you would NOT see all the galaxies (except those in your own group) moving away from YOU

If we want to see what galaxies looked like at a time close to the beginning of the universe, where should we look?

d. in a direction away from the plane of the Milky Way, where we can see very faint galaxies that are more than 10 billion light years away

Compared to the mass of our own Milky Way Galaxy, the total mass we estimate for the Andromeda Galaxy is

d. somewhat bigger

The new instrument that made it possible for Edwin Hubble to demonstrate the existence of other galaxies in the early 1920's was:

d. the 100-inch reflector on Mount Wilson

A friend of yours who is a science fiction fan hears you talk about the fact that astronomers now believe that the mechanism for the large energy output of quasars involves a supermassive black hole. He challenges you, saying something like "Oh come on, every science fiction fan knows that nothing, not even light, can escape from a black hole! How can a black hole be an energy source?" How would you respond to his objection?

d. the energy we see from quasars comes from regions where matter is falling in; these regions are still outside the event horizon

If a nearby galaxy still acts like a quasar today, what is the most likely explanation?

d. the galaxy must be undergoing a collision with another galaxy that is providing fresh fuel for its central black hole

How do quasars demonstrate that the universe evolves with time?

d. the number of quasars reached a maximum some time ago, and now the numbers have been declining

The reason type Ia supernovae are useful to astronomers for determining distances to other galaxies is that

d. they are very bright, and generally reach the same peak luminosity

One important way astronomers can learn in some detail about what happens when galaxies collide is

d. to simulate galaxy collisions on a large computer and watch what the simulation predicts

Which type of galaxy is very difficult to see, but (astronomers recently realized) may be very common?

dwarf elliptical

Which of the following was not done by Edwin Hubble?

e. discovering the relationship between period and luminosity of a cepheid variable

If quasars are at the distances most astronomers believe they are, then (for the most luminous ones) their luminosities must be:

e. like the combined luminosity of a hundred trillion (1014) Suns

Edwin Hubble was able to show that (with the exception of our nearest neighbors) the farther a galaxy is from us, the

e. the faster it is moving away from us

When astronomers make counts of how many quasars there are at different distances from us, what do they find?

e. the largest number of quasars can be seen at about the distance corresponding to a time when the universe was only 20% its current age (a time when the universe was still young)

If quasars often resemble little blue stars, what was it about them that so surprised astronomers when they were discovered?

e. their spectral lines were at first hard to recognize and then turned out to have large redshifts

Astronomers can now report that active star formation was going on at a time when the universe was only 20% as old as it is today. When astronomers make such a statement, how can they know what was happening inside galaxies way back then?

e. they examine the spectra of galaxies (or the overall colors of galaxies) with the highest redshifts they can find

Which type of galaxy is observed to contain mostly older stars?

elliptical

An astronomer needs to measure the distance to a globular cluster of stars that is part of the Milky Way Galaxy. What method should she try to use to find the distance?

find a variable star (cepheid or RR Lyrae) in the cluster

One of the main projects being carried out by the Hubble Space Telescope is to measure the distances of galaxies located in groups dozens of millions of lightyears away. What method do astronomers use with the Hubble to find such distances?

finding Cepheid variables and measuring their periods

What objects did Harlow Shapley use as "signposts" to figure out the extent of the Milky Way Galaxy and the location of its center?

globular clusters

In a distant galaxy, whose light is just arriving from 10 billion light years away, our spectroscope should reveal that the most common element is

hydrogen

What was especially noteworthy about the Sagittarius Dwarf Galaxy when it was discovered among the small galaxies near the Milky Way?

it was on a collision course with the Milky Way and would be swallowed by it eventually

Radio astronomy has played a pivotal role in showing us the detailed structure of the Milky Way Galaxy. Which of the following techniques would a radio astronomer use as an essential part of an investigation of this structure?

measuring the Doppler shift of a line in a radio spectrum

If a galaxy contains a great deal of dark matter, then, compared to the mass-to-light ratio of the inner part, the mass-to-light ratio of the whole galaxy will be

more

A graduate student in astronomy needs to measure the mass of a spiral galaxy she is studying for her PhD thesis. Which of the following observations would be important for her to make?

obtain the speed at which stars or gas near the outer regions of the galaxy are moving around

The type of galaxy that sometimes has a distinct bar of stars running across the central region is

spiral

The Tully-Fisher relation (looking at rotation speeds) only works for:

spiral galaxies

Which of the following is NOT part of the growing chain of evidence that makes many astronomers suspect there is a black hole at the very center of the Milky Way Galaxy?

the Hubble Space Telescope has shown us a visible-light image of an accretion disk at the center of the Galaxy

Which of the following statements about the nuclear bulge of our Galaxy is FALSE?

the best way to learn more about it is to observe higher energy radiation, such as ultraviolet and x-rays

Astronomers believe that the center of our Galaxy has a black hole with enough mass inside to make almost 4 million Suns! How do astronomers think a black hole could acquire so much mass?

the center of our Galaxy is a much more crowded region than where the Sun is found; we still see material falling toward the center and material has fallen in for billions of years

William Herschel thought that the Sun and Earth were roughly at the center of the great grouping of stars we call the Milky Way. Today we know this is not the case. What was a key reason that Herschel did not realize our true position in the Milky Way?

the dust that extends throughout the disk of the Galaxy only allowed Herschel to see the small part of the Milky Way that surrounds us

Which of the following is evidence that the formation process of our Galaxy may have included collisions with smaller neighbor galaxies?

the observation of long moving streams of stars that continue to orbit through our Galaxy's halo

What leads astronomers to conclude that the proto-galactic cloud (the cloud from which our Galaxy formed) was roughly spherical?

the oldest stars in the Galaxy (Population II stars, globular clusters) form a spherical halo around the Galaxy; they outline the original shape of the cloud that gave the Galaxy birth

Edwin Hubble developed a classification scheme for galaxies. By what characteristic did he classify galaxies?

their shape

Recently, astronomers have observed stars and other objects that orbit the center of the Milky Way Galaxy farther out than our Sun, but move around faster than we do. How do astronomers think such an observation can be explained?

there must be a great deal of invisible dark matter outside the orbit of the Sun whose gravitational pull explains the faster motions we see out there

Among irregular galaxies, what makes the Large and Small Magellanic Cloud especially useful for astronomers?

they are (for galaxies) very close to us, so they are easy to study

How do astronomers measure the mass that the Galaxy contains inside the orbit of the Sun?

they measure the distance to the center of the Galaxy and the period of the Sun's orbit and then use Kepler's Third Law

The Andromeda Galaxy (our nearest spiral neighbor) has spectral lines that show a blue shift. From this we may conclude that:

this particular nearby galaxy is moving toward us

A distant quasar shows a large redshift -- one so large, in fact, that the features we now see in the visible-light region of the spectrum would be invisible to us, were it not for the redshift. What band of the electro-magnetic spectrum were these features most likely in, before the spectrum was redshifted?

ultraviolet

What have we learned from the work of Harlow Shapley and others about the location of the Sun in the Milky Way Galaxy?

we are in the disk of the Galaxy, about 3/5 of the way from the center