Final Exam

Front 1

Suppose you tried to determine where we are in the galaxy by looking in different directions to see how many stars you could see. You would find ____

Back 1

Us in the center of the galaxy

Front 2

Why does a simple survey, such as described in the previous question, give a FALSE answer

Back 2

Interstellar dust blocks your view. We are in the center of what we can see, but we miss a lot of the Milky Way

Front 3

Since dust scatters blue light more than red, stars seen through a lot of interstellar dust would look ___

Back 3

redder than expected for their spectral type

Front 4

Why is it difficult to get a good picture of what our Milky Way galaxy looks like

Back 4

All of the above

Front 5

How do we get a good picture of what our Milky Way galaxy looks like

Back 5

We use infrared or microwaves to penetrate the dust and we use radio telescopes to see whre clouds of hydrogen gas are

Front 6

About how long does light take to reach us from the nearest star besides the Sun

Back 6

About 4 years

Front 7

About how long does light take to cross the disk of out Milky Way galaxy

Back 7

About 120,000 years

Front 8

Give several viable ways to estimate the mass of our galaxy

Back 8

Make an estimate of the number of stars and multiply by the average mass of a star and Observe the speed of rotation using the Doppler shift. Knowing the orbital size and speed, calculate the mass with Kepler's law

Front 9

When you calcuate the Milky Way's mass using the two correct methods from the previous question, what do you find

Back 9

The mass you estimate for all the visible stars is only about 1/10 the mass you get from observing motions

Front 10

Stars we see in the halo of our galaxy (or in globular clusters) formed even before the Milky Way collapsed into a disk. Since we see them now, they must be

Back 10

old and low mass

Front 11

How do the elements produced in massive stars get into other stars

Back 11

Supernovae blow them out into space, red giant winds blow them into space, the star-gas cycle circulate them

Front 12

Infrared telescopes penetrate dust and show us that stars at the center of the MWG are orbiting very fast. Which answer below best explains this behavior

Back 12

There probably is a massive black hole at our galaxy's center, with strong activity

Front 13

Which ONE of the following statements about types of galaxies is NOT true

Back 13

Elliptical galaxies are bluer and contain more dust than spiral galaxies

Front 14

The most basic difference between elliptical galaxies and spiral galaxies is that

Back 14

elliptical galaxies lack anything resembling the disk of a spiral galaxy

Front 15

Hubble's galaxy classification diagram (the tuning fork)

Back 15

relates galaxies according to their shapes, but not according to any evolutionary status

Front 16

Using the technique of main-sequence fitting to determine the distance to a star cluster requires that

Back 16

we have telescopes powerful enough to allow us to identify the spectral types of many individual main-sequence stars in the cluster

Front 17

Suppose we observe a Cepheid variable in a distant galaxy. The Cepheid brightens and dims with a regular period of about 10 days. What good will this observation do us?

Back 17

We will be able to use its period to determine its luminosity and hence (if we also measure the apparent brightness) to calculate the distance to its galaxy

Front 18

In 1924, Edwin Hubble proved that the Andromeda Galaxy lay far beyond the bounds of the Milky Way, thus putting to rest the idea that it might have been a cloud within our own galaxy. How was he able to prove this?

Back 18

He observed individual Cepheid variable stars in Andromeda and applied the period-luminosity relation to determine their distance

Front 19

Does Hubble's law work well for galaxies in the Local group?

Back 19

No, because galaxies in the local group are gravitationally bound together

Front 20

Why are white dwarf supernovae more useful for measuring cosmic distances than massive star supernovae

Back 20

White dwarf supernovae all have roughly the same true peak luminosity, while massive supernovae come in a wide range of peak luminosities (due to their wide range of masses)

Front 21

Suppose an elliptical galaxy is so far away that we cannot see even its brightest stars individually. Which of the following techniques could allow us to measure its distance

Back 21

We could use a white dwarf supernova as a standard candle

Front 22

What does cosmological redshift do to light

Back 22

Stretches its wavelength

Front 23

The lookback time of the cosmological horizon is

Back 23

the age of the universe

Front 24

Why can't we see past the cosmological horizon

Back 24

Beyond the cosmological horizon, we would be looking back to a time before the universe was born

Front 25

Why do we call dark matter "darkk?"

Back 25

It emits no radiation of any wavelength that we have been able to detect

Front 26

The flat rotation curves of spiral galaxies tell us that they contain a lot of dark matter. Do they tell us anything about where the dark matter is located within the galaxy

Back 26

Yes, they tell us that the dark matter is spread throughout the galaxy, with most located at large distances from the galactic center; that is, out in the halo that surrounds the disk.

Front 27

It is more difficult to determine the total amount of dark matter in an elliptical galaxy than in a spiral galaxy. Why

Back 27

Elliptical galaxies lack the atomic hydrogen gas that we use to determine orbital speeds at great distance from the centers of spiral galaxies

Front 28

We define the Sun to have a mass=-to-light ration of 1 (in solar units). Therfore, a red giant star that has the same mass as the Sun but is 1,000 times as luminous as the Sun has a mss-to-light ratio of

Back 28

.001

Front 29

What does the temperature of the gas between galaxies in galaxy clusters tell us about the mass of the cluster

Back 29

The temperature tells us the average speeds of the gas particles, which are held in the cluster by gravity, so we can use these speeds to determine the cluster mass

Front 30

How does gravitational lensing tell us about the mass of a galaxy cluster

Back 30

Using Einstein's general theory of relativity, we can calculate the cluster's mass from the precise way in which it distorts the light of galaxies behind it

Front 31

If WIMPs really exist and make up most of the dark matter in galaxies, which of the following is NOT one of their characteristics

Back 31

They travel at speeds close to the speed of light

Front 32

Why isn't space expanding within clusters of galaxies?

Back 32

Their gravity is strong enough to hold them together even while the universe as a whole expands

Front 33

Which of the following statements about galaxies and large-scale structures such as voids, clusters, superclusters, sheets and filaments is probably NOT true

Back 33

Clusters and superclusters appear to be randomly scattered about the universe, like dots sprinkled randomly on a wall

Front 34

According to current evidence, how does the actual average density of matter in the universe compare to the critical density

Back 34

The actual density of matter is many times higher than the critical density

Front 35

Which of the following statements BEST describes the current state of understanding regarding the apparent acceleration of the expansion of the universe

Back 35

We have strong observational evidence that the acceleration is real, but at this time we have little more than a name-dark energy-for what is causing this accelerated expansion.

Front 36

Some people think it would be better if we lived in a recollapsing universe that would eventually stop expanding and start contracting, rather than in an accelerating universe. For this to be the case, which of the following would have to be true?

Back 36

Dark energy does not exist and there is much more dark matter than we are aware of to date

Front 37

Components of the Milky Way Galaxy:

Back 37

flat disk; bright central bulge; spiral arms; dimmer, round halo surrounding everything; few hundred globular clusters circle the galaxy’s center

Front 38

stars in the disk all orbit in the

Back 38

same direction with a little up-and-down motion

Front 39

the Sun orbits the MWG once every

Back 39

230 Million years

Front 40

_____ give us a picture of our galaxy’s structure

Back 40

Radio mapping of neutral and ionized hydrogen regions

Front 41

ƒ____ maps the positions of globular clusters and correctly deduces that they center on a point 28,000 l-y from us, which must be the galactic center

Back 41

Harlow Shapley

Front 42

___—clouds of gas and dust—fill the galactic disk, obscuring our view in visible light

Back 42

The interstellar medium

Front 43

Because of the ___, astronomers were long fooled into thinking that our solar system was located near our galaxy’s
center

Back 43

interstellar medium

Front 44

The ____ is the center of our universe, not the Sun

Back 44

The MWG's globular clusters

Front 45

Our Sun lies in the outer part of the galactic disk, about _____ from its center.

Back 45

28,000 light years (8.5 kpc)

Front 46

Studying our galaxy is difficult because ____

Back 46

dust obscures our view and we are inside.

Front 47

A new survey by the Spitzer Space Telescope reveals that the Milky Way has only ___ main spiral arms, not the 4–5
previously thought.

Back 47

two

Front 48

The LMC and SMC are companion galaxies that orbit the MWG at distances of _____

Back 48

150,00 l-y (50 kpc)

Front 49

Another small galaxy—_____—lies even closer but is obscured from view by the MWG’s galactic plane.

Back 49

Sagittarius dwarf elliptical

Front 50

In the 1920s, ____ demonstrated that the MWG’s globular clusters are centered on a point thousands of
light years from our Sun. He correctly deduced that this point is the center of our galaxy, not our Sun

Back 50

Harlow Shapley

Front 51

___ lies in the outer part of the galactic disk, about 28,000 light years (8.5 kpc) from its center.

Back 51

Our Sun

Front 52

Studying our galaxy is difficult because

Back 52

dust obscures our view and we are inside

Front 53

The Sun is 28,000 l-y from the center of the galaxy and takes ___ to complete one orbit.

Back 53

230 million years

Front 54

____process of adding to the abundance of heavy elements.

Back 54

Chemical enrichment:

Front 55

Matter expelled from supernovae have enough velocity to escape our galaxy but interaction with the ____ keeps this matter (enriched with heavy elements) within the galaxy.

Back 55

interstellar medium

Front 56

ƒ_____ involves the following process: hot, ionized gas from exploding stars cools first to clouds of atomic hydrogen (H) and then cools further to clouds of
molecular hydrogen (H2)
ƒ these molecular clouds then can contract to form new stars more highly enriched in heavy elements
ƒ massive versions of these new stars will age and explode, beginning the process once again

Back 56

Star-gas-star cycle

Front 57

All stars return much of their mass to the interstellar medium via
ƒ

Back 57

stellar winds that blow throughout their lives “death events” of planetary nebulae or supernovae

Front 58

Recent observations show that our Sun is moving through a ____ as this cloud flows outwards
from the Scorpius-Centaurus Association star forming region. Our Sun may exit the Local Interstellar Cloud during the next 10,000 years.

Back 58

Local Interstellar Cloud

Front 59

___ ejected into space by winds from supergiants and supernovae sweeps up surrounding interstellar material, excavating a bubble of hot, ionized gas.

Back 59

High-speed gas

Front 60

Hot bubbles fill about ___ of the MWG’s disk

Back 60

20%–50

Front 61

The ___ is a cavity in the interstellar medium (ISM) of the Orion Arm of the Milky Way and is at least 300
light years across. The Solar System has been traveling through the ____ for the last 3 million years.

Back 61

Local Bubble

Front 62

The supernova shock wave can also accelerate electrons near to the speed of light, creating a radio emission called
_____.

Back 62

synchrotron radiation

Front 63

Supernovae can also generate ____, which are composed of electrons, protons, and atomic nuclei that are accelerated nearly to the speed of light.

Back 63

cosmic rays

Front 64

The ____ states that fountains of hot gas rise from the disk into the halo through elongated bubbles carved by blowouts. This model is difficult to verify at present.

Back 64

galactic fountain model

Front 65

Astronomers have detected over ___ different kinds of molecules, including water (H2O), ammonia (NH3), and ethyl alcohol (C2H5OH)

Back 65

120

Front 66

Gravitational forces in molecular clouds gather molecules into the ____ that eventually become protostars

Back 66

compact cores

Front 67

Once a few stars begin to form, UV radiation from high-mass stars ionize and heat the gas in the molecular cloud,
preventing much of the gas in the cloud from turning into stars. This process is called ____

Back 67

molecular cloud erosion.

Front 68

Hot blobs of gas—____are often found near these hot stars

Back 68

ionization nebulae (aka emission nebulae or H II regions)

Front 69

The most famous of the ionization nebulae is the ___

Back 69

Orion nebula

Front 70

_____—caused by light reflected off dust grains—appear blue because the red light is scattered by the
dust. A nice example is the nebulosity found around the main stars of the Pleiades cluster.

Back 70

Reflection nebulae

Front 71

____ are most likely caused by huge spiral density waves that cause gas, dust, and stars to bunch up into
long-term patterns.

Back 71

Spiral arms

Front 72

____ of the Milky Way excludes the dangerous inner regions and the metal poor outer regions of our
galaxy.

Back 72

Habitable zone

Front 73

ƒ often called Population II
ƒ most stars are old, red, dim, and smaller in mass than the Sun
ƒ heavy element concentrations 100X less (0.02% vs. 2%)
ƒ region is nearly gas-free compared to disk
ƒ stars formed early in the galaxy’s histor

Back 73

SPHEROIDAL POPULATION (HALO AND BULGE)

Front 74

ƒ often called Population I
ƒ contains both young and old stars all of which have heavy element proportions of 2%, like our Sun.

Back 74

Disk Population

Front 75

Our galaxy began as a giant ___ containing all the H and He that eventually became stars.

Back 75

protogalactic cloud

Front 76

Stars of the _____ formed first.

Back 76

spheroidal population

Front 77

____ from the galactic center suggest that tidal forces of suspected black holes occasionally tear apart chunks
of matter about to fall in.

Back 77

X-ray flares

Front 78

_____ are compact halos created as dust, gas and other debris are pulled toward a black hole
event horizon

Back 78

Black hole accretion disks

Front 79

The more massive a galaxy’s central bulge of stars, the heftier its supermassive black hole. Regardless of their size,
the bulges always turn out to be ___ as massive as the giant black holes at the hub of their galaxies.

Back 79

500 times