Multiple-Choice Questions

1) Interstellar gas is composed mainly of

A) only hydrogen.

B) 90% hydrogen, 9% helium by weight.

C) 10% hydrogen, 90% helium by numbers of atoms.

D) some hydrogen, but mainly carbon dioxide.

E) ammonia, methane, and water vapor.

Page Ref: 11.1

2) What effect does even thin clouds of dust have on light passing through them?

A) The light that passes though them is blue shifted due to the cloud's approach.

B) It dims and reddens the light of all more distant stars.

C) Even a little can completely block all light, such as the Horsehead Nebula.

D) Its motion causes the light of stars beyond to twinkle.

E) Its motion causes all light to be red shifted as it passes through these clouds.

Page Ref: 11.1

3) Which statement about the dark nebulae is true?

A) Hydrogen and helium are the chief absorbing and scattering agents.

B) They block the vast majority of radio waves from our Galaxy. 

C) They can be penetrated only with longer wavelengths such as radio and infrared.

D) They comprise the majority of the mass of the Galaxy.

E) They can be penetrated only with shorter waves, such as UV and x-ray.

Page Ref: 11.1


4) Some regions along the plane of the Milky Way appear dark because

A) there are no stars in these areas.

B) stars in that region are hidden by interstellar gas.

C) stars in that region are hidden by dark dust particles.

D) many brown dwarfs in those areas absorb light which they turn into heat.

E) many black holes absorb all light from those directions.

Page Ref: 11.1


5) Due to absorption of shorter wavelengths by interstellar dust clouds, distant stars appear

A) bluer.

B) brighter.

C) redder.

D) larger.

E) to have a higher radial velocit

Page Ref: 11.1


6) Which statement is true about the interstellar medium?

A) Gas contains a lot of carbon atoms.

B) Dust blocks the longest electromagnetic wavelengths.

C) Gas obscures the light from distant stars.

D) We know more about the gas than the dust.

E) Dust is spread uniformly through the galaxy.

Page Ref: 11.1


7) Spectra of interstellar gas show it has the same basic composition as

A) interstellar dust.

B) Earth's atmosphere.

C) stars.

D) asteroids.

E) the Martian polar caps.

Page Ref: 11.1


8) Emission nebulae like M-42 occur only near stars that emit large amounts of

A) visible light.

B) microwaves.

C) ultraviolet radiation.

D) infrared heat.

E) x-rays and gamma rays.

Page Ref: 11.2


9) What is the primary visible color of an emission nebula?

A) yellow because of dust.

B) blue from the scattering of light off the tiny molecules

C) red due to ionized hydrogen atoms

D) colorless, for hydrogen is crystal clear

E) black, for the dust associated with them absorbs all visible light

Page Ref: 11.2


10) The density of interstellar dust is very low, yet it still blocks starlight because

A) it is so cold it absorbs higher energy photons.

B) there is 100 times more opaque gas than dust present in the ISM.

C) the dust particles are about the same size as the light waves they absorb.

D) the dust particles are irregular in shape.

E) ice particles reflect all light back toward their stars, not toward us.

Page Ref: 11.2


11) The gas density in an emission nebula is typically a few ________ particles per cc.

A) dozen

B) hundred

C) thousand

D) hundred thousand

E) million

Page Ref: 11.2


12) What two things are needed to create an emission nebulae?

A) interstellar gas and dust

B) hydrogen fusion and helium ionization

C) cool stars and much interstellar dust

D) hot stars and interstellar gas, particularly hydrogen

E) hydrogen gas and carbon dust

Page Ref: 11.2


13) A large gas cloud in the interstellar medium that contains several type O and B stars would appear to us as 

A) a dark nebula.

B) an emission nebula.

C) bright blue.

D) a reflection nebula.

E) a dark patch against a bright background.

Page Ref: 11.2


14) Which of these is not a consequence of dust in the interstellar medium?

A) red light from the emission nebulae

B) reddening of stars' light that passes through the dust

C) blue reflection nebulae around the Pleiades

D) the dark nebulae that block 90% of the Milky Way from us visually

E) terrestrial planets like our own

Page Ref: 11.2


15) The most common molecule in a molecular cloud is

A) molecular hydrogen, made of two H atoms.

B) carbon monoxide, with one carbon and an oxygen.

C) methane, with four hydrogens around a hydrogen.

D) water, with two hydrogens around an oxygen.

E) ammonia, with three hydrogens attached to a nitrogen.

Page Ref: 11.3


16) Why are dark dust clouds largely misnamed?

A) They contain much more gas than dust.

B) The cloud is an illusion, for the dust is evenly distributed around the Galaxy.

C) Dust clouds do radiate energy, but not as much light as the stars do.

D) It is ice, not dust, which make them look dark.

E) All of the above are correct.

Page Ref: 11.3


17) Complex molecules in the interstellar medium are found

A) uniformly throughout the disk of the Galaxy.

B) scattered evenly throughout the universe, a product of the Big Bang itself.

C) only around the supergiant stars like Betelguese that make their heavy atoms.

D) primarily in the dense dust clouds.

E) on the surfaces of the coolest class K and M stars only.

Page Ref: 11.3


18) What information does 21 cm radiation provide about the gas clouds?

A) their motion

B) their distribution

C) their density

D) their temperature

E) all of these

Page Ref: 11.3


19) Neutral hydrogen atoms are best studied from their energy given off as

A) red hydrogen alpha emission, at 656.3 nm.

B) 121.3 nm as Lyman alpha emission in the UV.

C) 21 cm waves in the radio region.

D) .2 nm as x-rays.

E) Neutral hydrogen gives off no detectable radiation, since it is cold, not hot.

Page Ref: 11.3


20) The average temperature of the typical dark dust cloud is about

A) 0 K.

B) 2.73 K.

C) 100 K.

D) 3,000 K.

E) 6,000 K.

Page Ref: 11.3


21) Interstellar dust clouds are best observed at what wavelength?

A) Radio and infrared

B) visible only

C) UV and infrared

D) Radio and x-ray

E) Visible and UV

Page Ref: 11.3


22) When an electron in H changes its spin from the same to the opposite direction as the proton, it

A) emits an x-ray photon.

B) absorbs a radio wave photon.

C) emits a radio wave photon.

D) absorbs a visible light photon.

E) neither emits nor absorbs a photon.

Page Ref: 11.3


23) A newly formed protostar will radiate primarily at which wavelength? 

A) visible light

B) x-ray 

C) infrared

D) ultraviolet

E) radio

Page Ref: 11.4


24) During a protostar's T Tauri phase, it

A) begins a period of reduced activity.

B) expands dramatically.

C) lies on the main sequence.

D) may develop very strong winds.

E) changes its spin direction.

Page Ref: 11.4


25) What is the critical core contraction temperature for ZAMS stars?

A) 3,000 K

B) 5,800 K

C) 1 million K

D) 15 million K

E) 100 million K

Page Ref: 11.4


26) Which statement about the stages of starbirth is false?

A) At stage 1, only the cloud exists.

B) By stage 3, the star has formed a photosphere.

C) nuclear reactions begin in the core by stage 4.

D) The T-Tauri wind is prevalent in stage 5.

E) By stage 7, the star has reached the main sequence.

Page Ref: 11.4


27) On an H-R diagram, a protostar would be

A) above and to the right of the main sequence.

B) below and to the left of the main sequence.

C) below and near the right side of the main sequence.

D) above and near the upper left of the main sequence.

E) on the main sequence at the extreme lower right.

Page Ref: 11.4


28) The single most important determinant of the temperature, density, radius, luminosity, and pace of evolution of a protostar is its

A) chemical composition.

B) magnetic field.

C) spin.

D) mass.

E) molecular composition.

Page Ref: 11.5


29) A cloud fragment too small to collapse into a main sequence star becomes a

A) white dwarf.

B) pulsar.

C) T Tauri object.

D) brown dwarf.

E) planet of another star.

Page Ref: 11.5


30) How long does it take an M class star to reach the main sequence, compared to a solar type star?

A) a tenth as long

B) about the same, 30 million years

C) about twice as long

D) about twenty times longer

E) longer than the age of the Galaxy

Page Ref: 11.5


31) A fragment of a collapsing gas cloud that comes to equilibrium with a central temperature of 4 million K will become a

A) black hole.

B) brown dwarf

C) black dwarf

D) T Tauri star.

E) stage 1 protostar.

Page Ref: 11.5


32) All globular clusters in our Milky Way are about how old?

A) less than a million years

B) ten-fifty million years old

C) one to three billion years old

D) around ten billion years old

E) a variety of ages, from newly born to twenty billions years old

Page Ref: 11.6


33) What are the characteristics of an open cluster?

A) old age and tens of thousands of stars

B) no stars left on the main sequence, but millions of white dwarfs

C) a few hundred stars, most still on the main sequence

D) a star forming region, hundreds of light years across, with many blue MS stars

E) millions of stars, both young and old, spread out over 100,000 ly.

Page Ref: 11.6


34) Which is characteristic of globular star clusters?

A) old age and hundreds of thousands of stars, only about 30 ly wide

B) no remaining MS stars, but millions of white dwarfs

C) only brown dwarfs in a yellow ball 100 ly across

D) bright blue main sequence stars, and thousands of them

E) a mix of old and young stars, about 100,000 ly across

Page Ref: 11.6


35) Which of these would typically be the brightest star in a young open cluster?

A) G2V

B) B1V

C) A2Ib


E) M3Ia

Page Ref: 11.6


36) Why are star clusters ideal "laboratories" for stellar evolution?

A) The combined light of all the stars makes them easier to see.

B) Like our Sun, they lie in the plane of the Milky Way.

C) Their stars are all about the same age, composition, and distance from us.

D) Their stars are all about the same mass and temperature.

E) Their stars are all the same composition and stage in evolution.

Page Ref: 11.6


37) Most stars in our part of the Galaxy are formed

A) alone.

B) in open clusters of a few dozen.

C) in associations of thousands of stars across a spiral arm of the Galaxy.

D) in globular clusters of millions of stars.

E) in a singular event just after the Big Bang.

Page Ref: 11.6


38) Which of these would be the brightest star in an ancient globular cluster?

A) O3

B) B3

C) A4

D) K3

E) M5

Page Ref: 11.