Chapter 11 Review TRUE/FALSE. Write 'T' if the statement is true and 'F' if the statement is false. 1) Light from distant stars that must pass through dust arrives bluer than when it left its star. 1) 2) Interstellar matter is distributed very evenly throughout the galaxy. 2) 3) The gas in the interstellar medium consists of mostly heavy elements. 3) 4) Emission nebulae are created by gas absorbing ultraviolet energy from the hot young stars within them, such as in the Orion Nebula. 4) 5) O and B type stars are usually found associated with emission nebulae. 5) 6) Emission nebulae get their red color from the red supergiants forming in them. 6) 7) We usually find dark molecular clouds beside bright emission nebulae. 7) 8) Dark dust clouds are optically invisible, but give off radio energy. 8) 9) 21-cm radiation is a result of an electron in hydrogen flipping its spin direction. 9) 10) Stars evolve along the main sequence. 10) 11) Young open clusters contain a lot of hot, young blue-white stars. 11) 12) Globular clusters contain mostly blue stars. 12) 13) A star cluster with a lot of hot, blue stars must be relatively young. 13) MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 14) Interstellar gas is composed mainly of 14) A) ammonia, methane, and water vapor. B) 90% hydrogen, 9% helium by weight. C) only hydrogen. D) 10% hydrogen, 90% helium by numbers of atoms. E) some hydrogen, but mainly carbon dioxide. 15) What happens to light passing through even thin clouds of dust? 15) A) The light that passes through them is blue shifted due to the cloud's approach. B) Its motion causes the light of stars beyond to twinkle. C) Its motion causes all light to be red shifted as it passes through these clouds. D) Even a little can completely block all light, such as the Horsehead Nebula. E) It dims and reddens the light of all more distant stars. 1
16) Some regions along the plane of the Milky Way appear dark because 16) A) stars in that region are hidden by dark dust particles. B) stars in that region are hidden by interstellar gas. C) many black holes absorb all light from those directions. D) there are no stars in these areas. E) many brown dwarfs in those areas absorb light, which they turn into heat. 17) The spectra of interstellar gas clouds show that they have the same basic composition as 17) A) Earth's atmosphere. B) the Martian polar caps. C) interstellar dust. D) stars. E) asteroids. 18) What two things are needed to create an emission nebula? 18) A) cool stars and much interstellar dust B) interstellar gas and dust C) hydrogen gas and carbon dust D) hydrogen fusion and helium ionization E) hot stars and interstellar gas, particularly hydrogen 19) The most common molecule in a molecular cloud is 19) A) water, H2O. B) carbon monoxide, CO. C) ammonia, NH3. D) molecular hydrogen, H2. E) methane, CH4. 20) Complex molecules in the interstellar medium are found 20) A) only around the supergiant stars like Betelgeuse that make their heavy atoms. B) uniformly throughout the disk of the Galaxy. C) on the surfaces of the coolest class K and M stars only. D) primarily in the dense dust clouds. E) scattered evenly throughout the universe, a product of the Big Bang itself. 21) The average temperature of the typical dark dust cloud is about 21) A) 0 K. B) 6,000 K. C) 2.73 K. D) 3,000 K. E) 100 K. 22) When an electron in a hydrogen atom changes its spin from the same to the opposite direction as the proton, it A) absorbs a radio wave photon. B) emits an X-ray photon. C) absorbs a visible light photon. D) emits a radio wave photon. E) neither emits nor absorbs a photon. 22) 2
23) During the T-Tauri phase of a protostar, it 23) A) expands dramatically. B) may develop very strong winds. C) begins a period of reduced activity. D) lies on the main sequence. E) changes its spin direction. 24) At what core temperature does hydrogen begin to fuse to helium? 24) A) 10 million K B) 100 million K C) 1 million K D) 5,800 K E) 3,000 K 25) On an H-R diagram, a protostar would be 25) A) above and to the right of the main sequence. B) below and to the left of the main sequence. C) on the main sequence at the extreme lower right. D) below and near the right side of the main sequence. E) above and near the upper left of the main sequence. 26) The single most important determinant of the temperature, density, radius, luminosity, and pace of evolution of a protostar is its A) magnetic field. B) molecular composition. C) chemical composition. D) mass. E) spin. 26) 27) A cloud fragment too small to collapse into a main sequence star becomes a 27) A) pulsar. B) T-Tauri object. C) brown dwarf. D) white dwarf. E) planet of another star. 28) What are the characteristics of an open cluster of stars? 28) A) mostly found above and below the galactic plane B) All stars are about the same age and luminosity. C) a few hundred, mostly main-sequence stars D) All stars are much more massive than our Sun. E) old age and millions of members 29) Which is characteristic of globular star clusters? 29) A) no remaining main sequence stars, but millions of white dwarfs B) old age and hundreds of thousands of stars, only about 30 ly wide C) only brown dwarfs in a yellow ball 100 ly across D) a mix of old and young stars, about 100,000 ly across E) bright blue main sequence stars, and thousands of them 3
30) Why are star clusters ideal "laboratories" for stellar evolution? 30) A) Their stars are all about the same age, composition, and distance from us. B) The combined light of all the stars makes them easier to see. C) Like our Sun, they lie in the plane of the Milky Way. D) Their stars are all the same composition and stage in evolution. E) Their stars are all about the same mass and temperature. SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 31) Of all forms of electromagnetic energy, radiation gives us the least access to our entire Milky Way Galaxy. 31) 32) A region of ionized gas and dust, with imbedded hot young stars, is an. 32) 33) A reflection nebula appears blue because it scatters the light of the stars near it. 33) 34) Neutral hydrogen can be detected because its electron occasionally its spin and creates the 21-cm emission line for radio observers. 34) 35) Molecules are found only in the clouds of the interstellar medium. 35) 36) In its stage, the new protostar's solar winds will form bi-polar jets as the star's magnetic field intensifies. 36) 37) A star of five solar masses would reach the main sequence much than our Sun. 37) 38) Bright blue stars are typical of young star clusters. 38) 39) The Pleiades (or Seven Sisters) an example of an. 39) 40) In typical globular clusters, the brightest stars are. 40) ESSAY. Write your answer in the space provided or on a separate sheet of paper. 41) What is the critical temperature for stage 7; why? 42) Why do new stars generally form in close proximity? 43) Jupiter and the Sun have almost the same composition and density; why isn't Jupiter also a star? 44) Contrast the brightest stars of young open and old globular clusters. 45) Contrast the appearance of the H-R diagrams of a young open and old globular cluster. 46) Contrast open and globular star clusters. 4
Answer Key Testname: REVIEW11 1) FALSE 2) FALSE 3) FALSE 4) TRUE 5) TRUE 6) FALSE 7) TRUE 8) TRUE 9) TRUE 10) FALSE 11) TRUE 12) FALSE 13) TRUE 14) B 15) E 16) A 17) D 18) E 19) D 20) D 21) E 22) D 23) B 24) A 25) A 26) D 27) C 28) C 29) B 30) A 31) light or optical or visual 32) emission nebula 33) blue or shorter wavelength 34) flips or switches or reverses 35) darkest and densest and coldest. 36) T-Tauri or fifth 37) sooner or quicker 38) open 39) open cluster 40) red giants 41) The core must reach 15 million degrees K for the outward pressure generated by hydrogen fusion to balance the inward pull of gravity. 42) As a gas cloud collapses, it breaks into smaller fragments. Each of these fragments in turn break into still smaller fragments. As the process continues, the small fragments become protostars and then stars. 43) Jupiter does not have enough mass to generate the 10 million degree central core temperature to sustain the proton-proton chain necessary to become a star. 44) Hot, blue, main-sequence stars light up young open clusters, but aging globular clusters have long since lost such short-lived massive stars; they have red giants as their brightest, most evolved survivors. 5
Answer Key Testname: REVIEW11 45) In a young cluster, the main sequence is well defined, particularly to the top left, but as these massive stars evolved rapidly, in an old globular the top left portion is missing, and evolved red giants now populate the top right portion of the diagram. 46) Globular clusters are older (as old as the Galaxy, from 10-12 billion years old), contain many more stars (millions of stars for the richest ones), and are very poor in metals. Their brightest members have evolved into red giants, and their color magnitude diagram leaves the main sequence just above the Sun's position and curve into the giant branch to the top right. By contrast, most open clusters are much younger, with hot blue stars the brightest. They are made of a much larger fraction of heavy elements, produced by the many generations of supernovae that happened since the globular clusters formed. 6