5) What spectral type of star that is still around formed longest ago? 5) A) F B) A C) M D) K E) O

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1 HW2 Name MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) The polarization of light passing though the dust grains shows that: 1) A) the dust grains are elongated in shape. B) the dust grains are aligned by a weak interstellar magnetic field. C) the dust grains are chiefly made of iron. D) Both A and B are correct. E) All of the above are correct. 2) What makes the subject of star formation so difficult and complex? 2) A) It is so slow that no visible proof of it exists. B) Shock waves disrupt the orderly evolution of stars. C) Clouds, fragments, protostars, stars, and nebulae all interact and influence each other. D) Star formation is too expensive to study in detail. E) Stars live too long to be observed from birth to death. 3) A star (no matter what its mass) spends most of its life: 3) A) as a red giant or supergiant. B) as a protostar. C) as a main sequence star. D) as a T Tauri variable star. E) as a planetary nebula. 4) When a star's inward gravity and outward pressure are balanced, the star is said to be: 4) A) in rotational equilibrium. B) in thermal expansion. C) a stage 2 protostar. D) in gravitational collapse. E) in hydrostatic equilibrium. 5) What spectral type of star that is still around formed longest ago? 5) A) F B) A C) M D) K E) O 6) What spectral type of star that is still around formed most recently? 6) A) K B) A C) F D) M E) O 7) At which stage in a Sun-like star's life is its core the least dense? 7) A) Planetary Nebula B) Helium Fusion C) White Dwarf D) Main Sequence E) Subgiant Branch 8) Which of the following elements contained in your body is NOT formed in the cores of stars during thermonuclear fusion? A) aluminum B) carbon C) calcium D) hydrogen E) iron 8) 9) What temperature is needed to fuse helium into carbon? 9) A) 5,800 K B) one billion K

2 C) 15 million K D) 100 million K E) 100,000 K 10) The "helium flash" occurs at what stage in stellar evolution? 10) A) in the middle of the main sequence stage B) planetary nebula C) when the T Tauri bipolar jets shoot out D) horizontal branch E) red giant 11) During the hydrogen shell burning phase: 11) A) hydrogen is burning in the central core. B) helium is burning in the core. C) the core is expanding. D) the star grows more luminous. E) the star becomes less luminous. 12) A star is on the horizontal branch of the H-R diagram. Which statement is true? 12) A) It is burning both hydrogen and helium. B) The star is contracting. C) It is about to experience the helium flash. D) The star is about to return to the main sequence. E) It is burning only helium. 13) What inevitably forces a star like the Sun to evolve away from being a main sequence star? 13) A) Helium builds up in the core, while the hydrogen burning shell expands. B) The star uses up all its supply of hydrogen. C) The carbon detonation explodes it as a type I supernova. D) The core begins fusing iron. E) The core loses all its neutrinos, so all fusion ceases. 14) Just as a low-mass main sequence star runs out of fuel in its core, it actually becomes brighter. How is this possible? A) Its outer envelope is stripped away and we see the brilliant core. B) It immediately starts to fuse helium. C) It explodes. D) Helium fusion gives more energy than hydrogen fusion does, based on masses. E) The core contracts, raising the temperature and increasing the size of the region of hydrogen shell-burning. 14)

3 15) Refer to the figure above. What is the name of the path between the points labeled 8 and 9? 15) A) planetary nebula B) red giant branch C) horizontal branch D) asymptotic giant branch E) white dwarf 16) Refer to the figure above. What is the name of the path between the points labeled 10 and 11? 16) A) planetary nebula B) red giant branch C) horizontal branch D) asymptotic giant branch E) white dwarf 17) Our Sun, along with most of the stars in our neighborhood, probably formed: 17) A) at the beginning of the universe. B) hundreds of millions of years ago. C) about 10 million years ago. D) billions of years ago. E) a few million years ago. 18) What is the force that keeps a main sequence star from blowing apart? 18) A) radiation pressure B) magnetism C) gravitation D) electron degeneration pressure E) the strong force 19) Which event marks the birth of a star? 19) A) collapse of an interstellar cloud

4 B) formation of a photosphere C) instability in an interstellar cloud D) formation of the planetary nebula E) fusion of hydrogen atoms into helium atoms 20) What happens when an interstellar cloud fragment shrinks? 20) A) Temperature rises. B) Density rises. C) Pressure rises. D) It first becomes opaque. E) All of the above. 21) During a protostar's T Tauri phase, it: 21) A) begins a period of reduced activity. B) expands dramatically. C) changes its spin direction. D) lies on the main sequence. E) may develop very strong winds. 22) A newly formed protostar will radiate primarily at which wavelength? 22) A) ultraviolet B) infrared C) radio D) X-ray E) visible light 23) How long does it take for a star like our Sun to form? 23) A) 4.6 billion years B) fifty million years C) 100 thousand years D) two million years E) one billion years 24) A typical protostar may be several thousand times more luminous than the Sun. What is the source of this energy? A) the ionization of the gas as it heats up B) chemical combustion of hydrocarbons C) from the release of gravitational energy as the protostar continues to shrink D) nuclear fusion in its core E) from nearby hot stars or supernovae that have initiated the star formation process 24) 25) As a star forms, the photosphere first appears: 25) A) when contraction slows down. B) when the protostar forms. C) when nuclear fires ignite. D) when the planetary nebula is expelled. E) when the star reaches the main sequence. 26) At what stage of evolution do T Tauri stars occur? 26) A) just prior to the protostar stage B) just after the planetary nebula is expelled C) just as the collapsing cloud becomes luminous

5 D) after the star has established itself as a main sequence star E) when a protostar is on the verge of becoming a main sequence star 27) What is characteristic of a main sequence star? 27) A) The rate of nuclear energy generated in the hydrogen to helium fusing core equals the rate radiated from the surface. B) It has rapid rotation and a strong stellar wind. C) It has a mass less than the Sun's. D) Nuclear fusion in the core varies due to the amount of gravitational contraction that occurs and which heavy elements are produced. E) All of the above are correct. 28) On an H-R diagram, a protostar would be: 28) A) above and near the upper left of the main sequence. B) below and near the right side of the main sequence. C) above and to the right of the main sequence. D) below and to the left of the main sequence. E) on the main sequence at the extreme lower right. 29) Interstellar gas is composed of: 29) A) 90% hydrogen, 9% helium by weight. B) some hydrogen, but mainly carbon dioxide. C) 10% hydrogen, 90% helium by numbers of atoms. D) ammonia, methane, and water vapor. E) only hydrogen. 30) What effect do even thin clouds of dust have on light passing through them? 30) A) It dims and reddens the light of all more distant stars. B) Its motion causes the light of stars beyond to twinkle. C) The light that passes through them is blue shifted due to the cloud's approach. D) Even a little can completely block all light, such as the Horsehead Nebula. E) Its motion causes all light to be redshifted as it passes through these clouds. 31) The of light passing through thin dust clouds lets us map the Galaxy's magnetic field. 31) A) polarization B) absorption C) ionization D) granulation E) diffraction 32) Which of the following describes the shape of dust particles, based on polarization of light? 32) A) diamonds B) cubes C) rodlike D) spheres E) disks 33) Some regions along the plane of the Milky Way appear dark because: 33) A) stars in that region are hidden by interstellar gas. B) many black holes absorb all light from those directions. C) there are no stars in these areas. D) many brown dwarfs in those areas absorb light which they turn into heat. E) stars in that region are hidden by dark dust particles. 34) Due to absorption of shorter wavelengths by interstellar dust clouds, distant stars appear: 34) A) brighter.

6 B) redder. C) larger. D) bluer. E) to have a higher radial velocity. 35) Which statement is true about the interstellar medium? 35) A) Gas contains a lot of carbon atoms. B) Dust is spread uniformly through the galaxy. C) Gas obscures the light from distant stars. D) We know more about the gas than the dust. E) Dust blocks the longest electromagnetic wavelengths. 36) The spectra of interstellar gas clouds show that they have the same basic composition as: 36) A) Earth's atmosphere. B) interstellar dust. C) stars. D) the Martian polar caps. E) asteroids. 37) The density of interstellar dust is very low, yet it still blocks starlight because: 37) A) the dust particles are about the same size as the light waves they absorb. B) it is so cold it absorbs higher energy photons. C) there is 100 times more opaque gas than dust present in the ISM. D) ice particles reflect all light back toward their stars, not toward us. E) the dust particles are irregular in shape. 38) The overall dimming of starlight by interstellar matter is called: 38) A) absorption. B) scattering. C) extinction. D) emission. E) reddening. 39) In the Milky Way galaxy, gas and dust are found: 39) A) in emission nebulae. B) in neutral hydrogen clouds. C) in dark nebulae. D) in molecular clouds. E) everywhere. 40) Which is the least dense? 40) A) interstellar gas B) the atmosphere of the Sun C) the atmosphere of Earth D) the atmosphere of Jupiter E) interstellar dust

7 1) D 2) E 3) C 4) E 5) C 6) E 7) D 8) D 9) D 10) E 11) D 12) A 13) A 14) E 15) B 16) D 17) D 18) C 19) E 20) E 21) E 22) B 23) B 24) C 25) B 26) E 27) A 28) C 29) A 30) A 31) A 32) C 33) E 34) B 35) D 36) C 37) A 38) C 39) E 40) E