Phys 1403 (Test 3)

Front 1

What are the main constituents of interstellar gas

Back 1

Hydrogen and helium

Front 2

Which constituent of interstellar matter obscures visible light?

Back 2

Dust

Front 3

What makes up 90 percent of interstellar gas?

Back 3

Hydrogen

Front 4

Which of the following describes the distribution of interstellar matter in the Galaxy?

Back 4

It is patchy throughout most of the Galaxy.

Front 5

Why are reflection nebulae blue and emission nebulae red?

Back 5

Reflection nebulae scatter blue light, and emission nebulae emit red light

Front 6

What type of nebula contains stars of spectral types O and B?

Back 6

An emission nebula

Front 7

Why is 21-cm radiation important?

Back 7

It enables us to study dark clouds in the interstellar medium.

Front 8

CO, HCN, NH3, H2O, and H2CO are examples of interstellar ________ observed by radio radiation coming from large, cold clouds.

Back 8

Molecules

Front 9

Which of the following best describes the shape of interstellar dust particles?

Back 9

Rodlike

Front 10

What observation has enabled astronomers to determine the approximate shape of interstellar dust particles?

Back 10

How they polarize light

Front 11

If you took a large sample of interstellar material and compressed it to the density and temperature typical of Earth's atmosphere, how would it probably appear?

Back 11

Much more opaque than Earth's air

Front 12

If an interstellar cloud lies between Earth and a hot star, we can detect its presence in the stellar spectrum of the star. Which of the following properties of the cloud CANNOT be determined from the stellar spectrum?

Back 12

All of the above properties can be determined.

Front 13

Despite its low density, dust can completely block starlight because of which of the following?

Back 13

The large distances involved

Front 14

The chemical composition of the interstellar medium is basically similar to that of _____.

Back 14

The Sun

Front 15

The density of atoms in the interstellar medium is most similar to _____.

Back 15

The interior of a TV tube

Front 16

Of the following objects, the one that shines most like an emission nebula shines is _____.

Back 16

A glowing fluorescent light tube

Front 17

Stars interact with emission nebulae by ____.

Back 17

Exciting their atoms enough to emit light

Front 18

A dark interstellar globule is about the same size as ____.

Back 18

The Oort cloud

Front 19

The Ophiuchi cloud, shown in Figure 18.13 ("Dark Dust Cloud"), is dark because ____.

Back 19

Starlight from behind the cloud does not penetrate the cloud

Front 20

If a proton and an electron within a hydrogen atom initially have parallel spins, then change to have antiparallel spins, the atom must ____.

Back 20

Emit energy

Front 21

The telescope best suited to observing dark dust clouds is _____.

Back 21

A radio telescope

Front 22

The largest interstellar clouds are _____.

Back 22

Molecular clouds

Front 23

Molecular clouds are routinely studied using spectral lines from all but which of the following?

Back 23

Molecular hydrogen

Front 24

As a clump of interstellar gas contracts to become a main-sequence star, its changing position on the H-R diagram tells us __________.

Back 24

How its outward appearance is changing

Front 25

After it reaches its highest point on the H-R diagram, how do the protostar's surface temperature and luminosity change as it approaches the main sequence?

Back 25

Its surface temperature increases, but its luminosity decreases.

Front 26

When does a newly forming star have the greatest luminosity?

Back 26

When it is a shrinking protostar with no internal fusion.

Front 27

When a newly forming star is at its greatest luminosity, what is its energy source?

Back 27

Gravitational contraction.

Front 28

How do the properties of long-lived stars compare to those of short-lived stars?

Back 28

-Long-lived stars begin their lives with less mass and a smaller amount of hydrogen fuel.

-Long-lived stars are less luminous during their main-sequence lives.

Front 29

A main-sequence star twice as massive as the Sun would last __________.

Back 29

Much less than half as long as the Sun.

Front 30

If stars A and B are both main-sequence stars and star A has a greater fusion rate than star B, which of the following statements hold(s)?

Back 30

-Star A must be more luminous than star B.

-Star A must be more massive than star B.

Front 31

What happens when an interstellar cloud fragment contracts?

Back 31

All of the above answers are correct. (Its pressure increases, its density increases, its temperature rises).

Front 32

Which of the following statements best describes globular clusters?

Back 32

They contain from hundreds of thousands to millions of stars and have a typical size of about 50 parsecs

Front 33

A small group of atoms does not collapse into a clump because ________ quickly disperses them.

Back 33

Heat

Front 34

What process characterizes the T Tauri phase of protostellar evolution?

Back 34

Violent surface activity resulting in strong protostellar winds

Front 35

What temperature is required to initiate nuclear fusion in a stellar core?

Back 35

10,000,000 K

Front 36

For gravity to contract a spinning interstellar cloud, what must be present in sufficient amount?

Back 36

Mass

Front 37

What event must occur in order for a protostar to become a full-fledged star?

Back 37

The onset of hydrogen fusion

Front 38

What event must occur in order for a protostar to become a full-fledged star?

Back 38

The onset of hydrogen fusion

Front 39

What is the key factor that determines the temperature, density, radius, luminosity, and pace of evolution for a prestellar object?

Back 39

Mass

Front 40

What is the meaning of zero-age main sequence?

Back 40

It is the band on the H-R diagram in which stars are arranged as they begin their extended period of stable nuclear fusion.

Front 41

What are brown dwarfs?

Back 41

Low-mass objects that never become stars

Front 42

How do astronomers know that stars (and their planetary systems) form from concentrations of interstellar material?

Back 42

All the pieces of evidence listed here contribute to this conclusion.

Front 43

How do high-mass stars aid in the star formation process?

Back 43

They create shock waves that compress the surrounding gas and trigger collapse.

Front 44

Why do star clusters provide excellent tests for theories of stellar evolution?

Back 44

The stars in any particular cluster formed at roughly the same time from the same primary material and under the same environmental conditions.

Front 45

Which of the following statements best describes open clusters?

Back 45

They typically contain a few hundred to a few tens of thousands of stars and are a few parsecs across.

Front 46

Why do stars tend to form in groups?

Back 46

A large interstellar cloud fragments into smaller clouds that eventually form star

Front 47

A star is in hydrostatic equilibrium when the outward push of pressure due to core burning is exactly in balance with the inward pull of gravity. When the hydrogen in a star’s core has been used up, burning ceases, and gravity and pressure are no longer in balance. This causes the star to undergo significant changes. Which of the following evolutionary changes would bring a star back into hydrostatic equilibrium?

Back 47

1) A small increase in the star’s internal pressure and temperature causes the star’s outer layers to expand and cool.

2) A small decrease in the star’s internal pressure and temperature causes the star’s outer layers to contract and heat up.

Front 48

Why don't stars live forever?

Back 48

They run out of nuclear fuel in their cores.

Front 49

Why is the depletion of hydrogen in the core of a star such an important event?

Back 49

The star will begin to change its structure drastically.

Front 50

When a star depletes its core supply of hydrogen, ________ dominates in the core and ________ dominates in the envelope.

Back 50

gravity; pressure

Front 51

Hydrogen-shell burning proceeds increasingly faster due to which of the following?

Back 51

Heat released from the core's contraction

Front 52

As a low-mass main-sequence star runs out of fuel in its core, it actually becomes brighter. How is this possible?

Back 52

The outer layers expand due to the higher rate of fusion in a shell around the dead core.

Front 53

What is the region of the Hertzsprung-Russell diagram known as the horizontal branch?

Back 53

It is a region of the H-R diagram where stars remain for a time as they undergo helium core fusion.

Front 54

How do astronomers explain the existence of "blue stragglers"?

Back 54

They are main-sequence stars whose evolution has been altered by mergers or binary companions, causing them to live longer than usual for a star of their spectral type.

Front 55

In a white dwarf, what is the source of pressure that ultimately halts its contraction?

Back 55

Electrons packed so closely that they become incompressible

Front 56

What is the primary composition of a white dwarf?

Back 56

Carbon

Front 57

What is a planetary nebula?

Back 57

An expanding shell of gas around a white dwarf star

Front 58

In its last stage of evolution, what will the Sun become?

Back 58

White dwarf

Front 59

What is the size of the core of a typical white dwarf star?

Back 59

About the size of Earth

Front 60

What property of a star cluster helps determine its age?

Back 60

Main-sequence turnoff

Front 61

What is the age range among the globular clusters associated with our Galaxy?

Back 61

The globular clusters range from 10 to 12 billion years old.

Front 62

What is a contact binary?

Back 62

Two nuclear-burning stellar cores surrounded by a single continuous common envelope

Front 63

If a newly forming star has an excess of heat, then it will likely have______.

Back 63

A slower contraction rate

Front 64

The gravitational contraction of an interstellar cloud is primarily the result of its_____.

Back 64

Mass

Front 65

The interstellar cloud from which our Sun formed was_______.

Back 65

Thousands of times more massive than the Sun

Front 66

A protostar that will eventually turn into a star like the Sun is significantly_________.

Back 66

More luminous

Front 67

Prestellar objects in which nuclear fusion never starts are referred to as________.

Back 67

Brown dwarfs

Front 68

The current theory of star formation is based upon______.

Back 68

Amassing evidence from many different regions of our Galaxy

Front 69

If the initial interstellar cloud in Figure 19.14 ("Generations of Star Formation") were much more massive, the result would be_______.

Back 69

The formation of more stars

Front 70

One of the primary differences between the Pleiades cluster, shown in Figure 19.17(a), and Omega Centauri, shown in Figure 19.18(a), is that the Pleiades cluster is much_______.

Back 70

Younger

Front 71

If the H-R diagram shown in Figure 19.18(b) ("Globular Cluster") were redrawn to illustrate a much younger cluster, the main-sequence turnoff would shift to__________.

Back 71

Higher temperature

Front 72

A typical open cluster will dissolve in about the same amount of time as the time since______.

Back 72

Dinosaurs walked on Earth

Front 73

A star will evolve off the main sequence when it uses up_____.

Back 73

Most of the hydrogen in the core

Front 74

On the main sequence, massive stars_____.

Back 74

Burn their hydrogen fuel more rapidly than the Sun

Front 75

Compared to other stars on the HR diagram, red-giant stars are so named because they are _____.

Back 75

Cooler

Front 76

When the Sun is on the red-giant branch, it will be found at the _____.

Back 76

Upper right

Front 77

After the core of a Sun-like star starts to fuse helium on the horizontal branch, the core becomes _____.

Back 77

Hotter

Front 78

If the evolutionary track in Overlay 3, showing a Sun-like star, were instead illustrating a significantly more massive star, it's starting point (stage 7) would be _____.

Back 78

Up and to the left

Front 79

A white dwarf is supported by the pressure of tightly packed _____.

Back 79

Electrons

Front 80

When the Sun leaves the main sequence, in Figure 20.3, "Red Giant on the H-R Diagram," It will become _____.

Back 80

Brighter

Front 81

A star like the Sun will end up as a _____.

Back 81

White dwarf

Front 82

Compared to the Sun, stars plotted near the bottom left of the H-R diagram are much _____.

Back 82

Denser

Front 83

Extinction

Back 83

Cloud blocking starlight

Front 84

Reddening

Back 84

A red hue appears on stars on edge of the cloud of gas - the same effect as the sunset.

Front 85

Doppler Broadening

Back 85

Wider spectral lines due to heated (more active) atoms moving quickly and causing a doppler shift.

Hot gas = wide spectral lines

Cool gas = thin spectral lines

Front 86

As a protostar collapses, it becomes_____.

Back 86

Smaller, hotter, and dimmer

Front 87

A star will eventually stabilize, meaning that for every bit of energy leaving, new energy is created. This marks the beginning of the_____.

Back 87

Main sequence

Front 88

Stars cannot form from protostars that are too_____.

Back 88

Big or small