astr121 exam 3

What created the Cosmic Microwave Background, or CMB?

Heat left over from the Big Bang

Where should you see open clusters in the Milky Way on the sky?

In the disk

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

If you want to check on what conditions were like in the universe a few hundred thousand years after the Big Bang, what sort of instrument would it be best to use:

a satellite with infrared and microwave telescopes on board

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

bluer and smaller

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

Factoring in everything we currently know about the history of the universe, our best estimate for the age of the universe is

about 13.8 billion years

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

Which of the following statements about dark matter is FALSE:

astronomers have a pretty good idea what the dark matter is made of

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

Astronomers believe that the large elliptical galaxies formed

from the collision and merger of many smaller fragments

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

Which are thought to be very old?

globular cluster planetary nebulae

Which occur only in spiral arms?

group of O and B stars giant molecular cloud open cluster

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 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

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?

in a globular cluster high above the Galaxy's disk

If I looked on a large scale and plotted the position of galaxy clusters, I would find them arranged:

in filaments and empty areas like a web

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

in the disk

Why do we call dark matter "dark?"

it doesn't emit or absorb light of any wavelength that we have been able to detect

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

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

How many galaxies show a red-shift?

nearly all of them

Which of the following is not a way that astronomers can find how much dark matter there is in cluster of galaxies?

observe the radio waves coming from all dark matter; from the strength of the radio waves from each cluster, estimate the amount of dark matter needed to produce them

Which are thought to be very young?

open cluster group of O and B stars giant molecular cloud

When do astronomers now think that the "dark energy" began to accelerate the expansion of the universe?

several billion years after the Big Bang

Which of the following did NOT happen during the first few minutes after the Big Bang?

some very massive early stars formed

Our Milky Way Galaxy is what type of galaxy?

spiral

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

spiral

Why do galaxies collide, while stars almost never do?

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

Which of the following is pretty good evidence that the universe began with a Big Bang?

the 3-degree cosmic microwave background radiation

The reciprocal of the Hubble constant (1/H) is a rough measure of the:

the age of the universe

How do astronomers currently think the amount of detectable (observable) matter in the universe compares to the amount of dark matter and dark energy? (Be careful here, we're taking dark energy into account)

the amount of detectable matter is far less than the amount of dark matter & energy (<5%)

Which of the following statements about our modern ideas of how spiral galaxies form and develop is TRUE?

the central bulges of spiral galaxies formed first and their disks formed later

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

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

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

their shape

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

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

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

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

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

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

What is the present best estimate of Hubble's constant?

~70 km/s/Mpc

Which have the hottest stars?

-young open clusters -some giant molecular clouds (those with stars) -group of O and B stars -planetary nebulae (remember they have a central stellar core leftover)

The Milky Way shows evidence that over its history it has merged with and "cannibalized" smaller galaxies.

True

The objects that made it possible for astronomers to discover the acceleration in the expansion of the universe were

Type Ia supernovae

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

At first, right after the Big Bang, the universe was too hot for nuclei and electrons to combine into the kinds of neutral atoms that are familiar to us today. How soon after the beginning did it become cool enough for neutral atoms to form? (i.e. nucleons with electrons, not just the nucleons)

a few hundred thousand years

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

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? i.e. Which type of emission will more easily make it through all the gas and dust in the galaxy?

a radio telescope that can observe at 21-cm wavelengths

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?

about 35 times the size of the Sun (0.3 AU)

Roughly how many galaxies make up our Local Group?

about 60 or so

What fraction of the Galaxy's mass is in a form that does not emit electromagnetic radiation?

about 85%

The rate of expansion of the universe is?

accelerating

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 these

The Population I stars in the Milky Way Galaxy...

all of these options

In the very distant future, given our best model of the accelerating universe, what will the universe look like?

all the stars will die and the galaxies will be dark

Astronomers now know that surrounding the main body of our Galaxy and our fainter halo of stars there is

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

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

According to the models of the universe we discussed in this course, why do the galaxies move apart (why do we have Hubble's law)?

as a result of the Big Bang, space itself is stretching, and this stretching carries the galaxies away from each other

In our modern view of the expansion of the universe, we understand that it is space that is stretching; individual galaxies don't speed away from each other as if they were rockets. In that case, why do galaxies show a red-shift?

as space stretches, the waves of radiation in space also stretch and their wavelength increases

Which of the following statements about the early universe (as envisioned by the standard model of cosmology) is FALSE?

at the very beginning, the energies were so great that the universe was actually contracting for a while

Which occur only in the parts of the Galaxy other than the spiral arms?

globular cluster planetary nebulae (most)

Which of the following is the Earth not located in?

globular cluster M-13

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

If the universe were decelerating, our calculated age of the universe would be:

less than 1/H

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

When we determine the age of the universe using the Hubble Time, what important simplifying assumption goes into our calculations?

that the expansion of the universe has been happening at the same rate - neither speeding up or slowing down

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

According to the most recent data from satellites making precise measurements of the properties of the cosmic microwave background

the dark energy makes up just a little less than 70% of the density of the universe, making it the most significant constituent of the mass-energy

After the Big Bang, in order for the universe to become transparent to light and other electro-magnetic radiation, what had to happen?

the density of the universe had to decrease (to 1000 nuclei per cubic centimeter or less)

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

If a very distant galaxy looks blue overall to astronomers, from this they can conclude that: (be careful with this one)

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

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 several smaller galaxies that were its neighbors

Recent observations indicate that the universe is expanding faster today than it was a few billion years ago (that, in other words, the expansion of the universe is accelerating.) What kind of observations have led astronomers to this surprising conclusion?

the measurement of galaxy distances using Type Ia supernovae

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

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

The estimated age of the Milky Way galaxy is about ___.

13 billion years

How do we think our Universe will end?

A big rip!

What is the Hubble tuning fork diagram?

A classification system for different types of galaxies based on their differences in visual appearance.

Of the normal matter in the Milky Way, the vast majority of the mass is in the form of gas and dust.

False

Why is the use of Hubble's Law to measure distances to galaxies so important to astronomers? (This one may require looking through your textbook since I've had to skip over most methods for determining distance)

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

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

Today, we believe that only a small number of elements were actually formed during the Big Bang. Which of the following was NOT one of these:

carbon

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)

Hubble's law indicates that...

All of these.

According to the density-wave theory, spiral arms are blue because they

Contain a lot of young stars formed from clouds compressed by the density wave.

What have scientists suggested is causing the Universe to expand faster?

Dark Energy

How does the Milky Way rotate?

Differentially

One of the reasons that Kapetyn underestimated the size of the Milky Way and Shapley overestimated it is that they did not recognize the ____.

Dimming effect of interstellar dust

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

Dwarf Elliptical

Astronomers can measure the diameter of our Milky Way Galaxy by plotting the position of globular star clusters.

True

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

Rotational velocity outside the visible boundary of our Galaxy is _____ than would be expected on the basis of observed stars and gas, indicating the presence of _____.

Higher; dark matter

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

Why is it not possible to use visible light to investigate the center of our Galaxy?

Intervening gas locating in the disk of the Galaxy blocks our view of the galactic center.

The cosmic microwave background is sometimes referred to as "relic radiation" -- light left over from a truly ancient time. But it isn't a relic of the universe's first moments, of the hot plasma posited by theorists; instead, it's thought to come from about 380,000 years after the very beginning, just after an epoch called "recombination." What happened during this time period?

Neutral hydrogen and helium atoms formed.

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

Sagittarius A

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

Which of the following statements about the spiral arms of the milky way is true?

The arms are populated by a large number of O and B type stars and they are sites of recent and ongoing star formation.

What is meant in cosmology by "critical density"?

The density that determines whether the Universe expands forever or re-collapses.

Why is the CMB so cool now?

The expansion of the Universe has cooled the radiation and stretched its wavelengths

What does a larger red-shift indicate?

The galaxy is moving away faster

The Milky Way is tilted on the sky because

The solar system is tilted compared to the disk of the galaxy.

Based on many surveys of the average density of matter in the universe (regular matter and dark matter), astronomers now conclude that the average density of the universe is: (To answer this, think about the role an increase in density (and thus gravity) has on the expansion of the universe)

essentially equal to zero (density is super low)

Where in space did the expansion of the universe begin?

everywhere at once