Astronomy 102 Test 4 study guide

Use Hubble's Law to calculate the recessional velocity of the Virgo cluster of galaxies. How fast are these galaxies receding away from us

1240 km/sec

The Andromeda Galaxy is the most distant celestial object that can be seen with the unaided eye. How far away from the Milky Way is the Andromeda Galaxy located

2.5 million light years

How far away are the galaxies of the Virgo cluster from the Milky Way

60 million light years

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

Maarten Schmidt

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

Milton Humason

What type of galaxy is NGC1317? (Use the diagram for Hubble's galaxy classification scheme to help you in answering this question

SBa

The rich galaxy cluster that is closest to our Local Group of galaxies is the

Virgo Cluster

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

How do astronomers know that there aren't significant amounts of dark matter within our solar system

a lot of dark matter would affect the motions (orbits) of our space craft as the move through the solar system

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

Roughly how many galaxies make up our Local Group

about 60 or so

. By examining rich clusters of galaxies, such as the Coma Clusters, astronomers have discovered that spiral galaxies

are found mostly in the outer regions of such clusters, not in the middle

When astronomers have examined rich clusters of galaxies with their instruments, they have found that these clusters

are more likely to contain giant elliptical galaxies than poor clusters

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

bluer and smaller

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 near by galaxy and using it to get the distance

According to our current understanding, giant elliptical galaxies form:

by the merger (or swallowing) of a number of smaller galaxies in a cluster of galaxies

The cosmological principle in astronomy

c. is confirmed by many observations done by Hubble and many other astronomers since

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

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

Which of the following was not done by Edwin Hubble

discovering the relationship between period and luminosity of a cepheid variable

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

dwarf elliptical

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

Which type of galaxy is observed to contain mostly older stars

elliptical

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

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

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

finding a redshift and using hubbles law

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

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

increase quiet a bit

How would you describe the shape of the Large Magellanic Cloud

irregular

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

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

most galaxies are so far away the only way to get distances to them is to use hubbles law

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

move away from us three times faster than A

How are galaxies and quasars related

quasars are active supermassive black holes at the centers of galaxies

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

redshifts that indicate they are far away

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

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

Our Milky Way Galaxy is what type of galaxy

spiral

If you wanted to write a complete "cosmic address" for yourself, including every location or structure you live in, which of the following would NOT be part of that address

the coma cluster

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

the discovery that the milky way galaxy has a black hole at the center with enough mass for 4 million suns

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

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?

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

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

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

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

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

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

An astronomer discovers a massive galaxy which has four nuclei. What is a likely explanation for a galaxy having more than one nucleus?

the galaxy must have swallowed the several smaller galaxies that were its neighbors

How do quasars demonstrate that the universe evolves with time?

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

In which of the following domains of the universe have astronomers NOT found evidence for the presence of dark matter today

the solar system

When astronomers say that the groups of galaxies are distributed isotropically, they mean that

the way galaxies are arranged in space looks the same in all directions

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

their shape

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

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

How does this elliptical galaxy differ in appearance from a spiral galaxy

there are no visible spiral arms

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

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

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

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

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

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

spiral galaxies

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

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

According to the Cosmological Principle, the universe

is isotropic and homogeneous

Which of the following is not true about the Local Group of galaxies (of which the Milky Way is a member)

it has about a thousand member galaxies

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

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

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

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

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)

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

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

somewhat bigger

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

spiral

How do astronomers currently think the amount of detectable (observable) matter in the universe compares to the amount of dark matter and dark energy

the amount of detectable matter is far less than the amount of dark matter and energy

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 hubbles law

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

from an accretion disk around the super massive black hole

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

galaxies contain many more stars that shine much less brightly than the sun

What do the surveys of the three-dimensional distribution of groups of galaxies reveal about how groups and clusters of galaxies are organized?

galaxy groups are organized into huge filaments with great voids between them something like the structure one would see taking a cross section of some soap bubbles

To map out how clusters of galaxies are distributed in the universe, astronomers needed to know where each cluster was in the sky AND

how far away from us each cluster was

Which of the following is a way that having an active galactic nucleus (AGN), with a supermassive black hole in the center, can affect the development of a galaxy

huge energetic jets from the accretion disk can disturb and lessen star formation in the galaxy

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

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

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

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

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?

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

For the Abell cluster of galaxies z = 0.14, and for the Virgo cluster z = 0.004. What can be said about the relationship between distance and redshift from this small sample of redshifts?

larger redshift values correspond to greater distance

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

like the combined luminosity of a hundred trillion (1014)suns

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)?

long ago, galaxy shapes were not (for the most part) regular and organized; galaxies looked chaotic and clumpy

Which of the following does NOT happen when two galaxies collide

many of the stars in one galaxy collide with the stars in the other

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

matter falling towards a super massive black hole at the center of the galaxy

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

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

. 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 location of the Milky Way galaxy is indicated. Extending outward in two directions from our Sun is an area called the Zone of Avoidance. This area does not appear to contain any galaxies. What might be the cause of this?

our view along this plane is obscured by gas and dust within the milky way

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

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

Why do galaxies collide, while stars almost never do

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

Sloan Digital Sky Survey

takes images and spectra of millions of objects, to find the positions and redshifts of as many galaxies and quasars as possible

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

the 100 inch reflector on mount wilson

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

the faster it is moving away from us

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

the jets are "spit out" from the chaotic accretion disks of super massive black holes in directions that are perpendicular to the disk

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

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

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?

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

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

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

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

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

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

type la supernova

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

The "great voids" that astronomers studying galaxies are finding are:

very large regions of intergalactic space, where relatively few galaxies or galaxy clusters can be found

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

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

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

vesto slipher

Which of the following can we NOT learn from studying the Doppler shifts in the spectrum of galaxies beyond our Local Group?

whether they have jupiter- mass planets around many of their stars