Deck 10: The Interstellar Medium

Question 1

Stars are born from the interstellar medium, and aging or dying stars return gas and dust back into the interstellar medium.

Answer 1

True

Question 2

At infrared wavelengths, the ISM glows with blackbody radiation emitted by the interstellar dust.

Answer 2

True

Question 3

Stars are born in reflection nebulae.

Answer 3

False

Question 4

Molecular clouds are mapped using _____ gas instead of the most-abundant hydrogen because it radiates at radio wavelengths more efficiently.

A) oxygen III
B) oxygen II
C) helium II
D) carbon monoxide
E) carbon dioxide

Question 5

Calculations of the Sun's future evolution indicate that it will blow away almost half of its mass in several relatively short episodes about 4 to 5 billion years from now before it is finally extinguished.

Question 6

The ground state of hydrogen has two closely-spaced energy levels, where one-electron is spinning up and the other is spinning down. This energy transition corresponds to releasing excess energy as a photon at what wavelength?

A) 21 centimeters
B) 21 millimeters
C) 21 meters
D) 22.2 centimeters
E) 22.2 millimeters

Question 7

Elements such as carbon, silicon and oxygen have been produced in stars and expelled as stars age in the interstellar medium. This is most likely due to these elements having cooled and condensed from aging stars to form dust grains, and carried out by a powerful winds.

Question 8

The composition of the interstellar dust suggests that it is formed primarily in the atmospheres of cool stars.

Question 9

H I clouds can be observed using _____.

A) optical telescopes above the Earth's atmosphere
B) 21-cm radiation
C) x-ray radiation
D) infrared radiation
E) ultraviolet radiation

Question 10

The emission lines from O III are called ____ because they are not visible laboratories on Earth due to the much greater pressure of the gas on Earth.

A) unique lines
B) unresolved lines
C) forbidden lines
D) unseen lines
E) "fathom" lines

Question 11

The interstellar medium is composed of mainly _____.

A) equal parts of gas and dust
B) mostly dust and some gas
C) mostly gas and some dust
D) dust only
E) gas only

Question 12

The ISM is easily visible to human eyes.

Question 13

H II Regions are also called emission nebulae.

Question 14

Because blue light has a shorter wavelength than red light, it will be more readily scattered.

Question 15

Nebula is just another name for the interstellar medium (ISM).

Question 16

X-rays come from certain regions of the interstellar medium because gas molecules in those regions are at a very high density.

Question 17

Observing at a wide range of wavelengths, astronomers have detected more than ______ different molecules in the ISM.

A) 10
B) 20
C) 50
D) 100
E) 150

Question 18

The coronal gas in the interstellar medium has very high temperatures similar to the Sun's corona.

Question 19

Interstellar extinction and the reddening of light by the interstellar medium (ISM) are both caused by _____.

A) atoms and molecules in the ISM
B) only atoms in the ISM
C) only molecules in the ISM
D) only dust in the ISM
E) dust, atoms, and molecules of the ISM

Question 20

The intercloud medium is believed to make up 90 percent of the mass of the interstellar medium.

Question 22

Coronal gas emits x-rays and has temperatures of ____.

A) 10⁶ K  o r  higher
B) more than 10⁴  K but less than 10⁶ K
C) 5000 K
D) between 1000 K to 5000 K
E) less than 500 K

Question 23

Large molecular clouds will form into protostars because of ____.

A) the thermal motions of the atoms in the gas cloud
B) gravitational contraction
C) radiation pressure from nearby stars
D) the temperature reaching a critical point
E) condensation of dust and gas

Question 24

Molecules in the interstellar medium emit radiation at what wavelengths?

A) radio
B) microwave
C) visible light
D) ultraviolet
E) X-ray

Question 25

What is the most abundant element in the interstellar medium?

A) carbon
B) iron dust
C) carbon dust
D) helium
E) hydrogen

Question 26

Which mission passed the bow shock in the Universe?

A) Cassini-Huygens
B) Interstellar Boundary Explorer
C) Voyager I
D) Voyager II
E) Kepler

Question 27

Which mission is mapping the heliosphere's boundary?

A) Cassini-Huygens
B) Interstellar Boundary Explorer
C) Voyager I
D) Voyager II
E) Kepler

Question 28

Which type of nebula is produced when a star, hotter than 25,000 K, excites the gas near it to produce an emission spectrum producing a distinctive pink color?

A) emission nebulae
B) H I
C) reflection nebulae
D) dark nebulae
E) spectral type B6

Question 29

If hydrogen (H₂) gas is the most common molecule found within the interstellar medium, then why do astronomers measure the amount of carbon monoxide (CO) gas to map molecular clouds?

Question 30

Which molecule has not been detected in molecular clouds?

A) ethyl alcohol
B) nitrous oxide
C) molecular hydrogen
D) carbon monoxide
E) All of these have been detected.

Question 31

List the three types of nebulae in the Interstellar Medium.

Question 32

The type of radiation that is emitted when the electron in a hydrogen atom experiences a spin flip is a(n) _______________.

Question 33

Which type of nebulae is produced when short-wavelength scatters from the dust and displays a blue hue?

A) emission nebulae
B) H I
C) reflection nebulae
D) dark nebulae
E) spectral type B6

Question 34

Which telescope imaged the center of the Milky Way Galaxy at a wavelength of 8 microns to reveal the distribution of the dusty interstellar medium?

A) Spitzer Space Telescope
B) infrared telescope
C) European Southern Observatory
D) X-ray telescope
E) radio telescope

Question 35

Which type of nebulaeare twisted and distorted clouds of gas and dust dense enough to obstruct the view of the more distant stars?

A) emission nebulae
B) H I
C) reflection nebulae
D) dark nebulae
E) spectral type B6

Question 36

Why doesn't warm, dense hydrogen emit 21-cm radiation?

Question 37

The _______________ is a high temperature, low density region in the interstellar medium around the Sun.

Question 38

Coronal gas radiates energy at ______________ wavelengths.

Question 39

The spacecraft ________ captured particles that scientists believe came from the ISM.

A) Chandra
B) Hubble
C) Interstellar Boundary Explorer
D) Voyager
E) Stardust

Question 40

The pressure of a gas depends on the ____ and ____ of the gas.

A) density; volume
B) temperature; density
C) temperature; mass
D) temperature; volume
E) density; mass

Question 41

Distinguish between pressure and density .   How are they related to each other?

Question 42

Which component of the interstellar medium has the greatest temperature?

Question 43

What observations indicate the presence of dust in the interstellar medium?

Question 44

What produces the coronal gas?

Question 45

Interstellar dust scatters _____________light more than _____________light.

Question 46

What observations demonstrate the existence of an interstellar medium?

Question 47

What are "forbidden lines"? Briefly describe how they form.

Question 48

Describe three ways in which astronomers can distinguish between interstellar absorption lines and stellar absorption lines.

Question 49

The interstellar reddening does not shift the _______________ of spectral lines, as does the Doppler effect.

Question 50

To an observer on Earth, dust in the interstellar medium will cause a star to appear _______________ and_______________than it really is.

Question 51

_______________ is believed to be produced by supernova explosions.

Question 52

______________ are cool, with temperatures of about 100 K and densities of ten to a few hundreds of atoms per cubic centimeter.

Question 53

H II emission nebula regions are found around _____________.

Question 54

Why is the sky blue during the day?

Question 55

_______________ require that a young hot star (T ≥ 25,000 K) be relatively nearby.

Question 56

Briefly discuss the gas-stars-gas cycle.