Ch 11 Name___________________________________ TRUE/FALSE. Write 'T' if the statement is true and 'F' if the statement is false. 1) There is as much mass in the voids between the stars as in the stars themselves. 1) 2) The dust particles have exactly the same chemical composition as the gases of the interstellar 2) medium. 3) Emission nebulae are created by gas absorbing ultraviolet energy from the hot young stars within 3) them, such as in the Orion Nebula. 4) O and B type stars are usually found associated with emission nebulae. 4) 5) Young open clusters contain a lot of hot, young blue-white stars. 5) MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 6) Some regions along the plane of the Milky Way appear dark because 6) A) there are no stars in these areas. B) stars in that region are hidden by dark dust particles. C) many brown dwarfs in those areas absorb light, which they turn into heat. D) many black holes absorb all light from those directions. E) stars in that region are hidden by interstellar gas. 7) The gas density in an emission nebula is typically about how many particles per cc? 7) A) hundred B) million C) dozen D) hundred thousand E) thousand 8) What information does 21-cm radiation provide about the gas clouds? 8) A) their density B) their temperature C) their motion D) their distribution E) all of these 9) During the T-Tauri phase of a protostar, it 9) A) lies on the main sequence. B) changes its spin direction. C) begins a period of reduced activity. D) may develop very strong winds. E) expands dramatically. 1 10) At what core temperature does hydrogen begin to fuse to helium? 10) A) 5,800 K B) 10 million K C) 3,000 K D) 1 million K E) 100 million K 11) On an H-R diagram, a protostar would be 11) 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) above and near the upper left of the main sequence. E) below and near the right side of the main sequence. 12) Why are star clusters ideal "laboratories" for stellar evolution? 12) A) Their stars are all about the same mass and temperature. B) The combined light of all the stars makes them easier to see. C) Their stars are all about the same age, composition, and distance from us. D) Their stars are all the same composition and stage in evolution. E) Like our Sun, they lie in the plane of the Milky Way. SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 13) Interstellar reddening and extinction are due to ________ in the interstellar medium. 13) 14) Red sunset, red lunar eclipses, blue skies, and reflection nebulae are all the result of the 14) ________ of visible light off tiny dust particles. 15) The Pleiades (or Seven Sisters) an example of an ________. 15) ESSAY. Write your answer in the space provided or on a separate sheet of paper. 16) Contrast the chemical composition of interstellar gas with that of interstellar dust. 17) A typical protostar may be several thousand times more luminous than our Sun; where does this energy come from? 18) What is a brown dwarf? 19) How does the mass of the protostar impact its future evolution? 20) Contrast open and globular star clusters. 2 Answer Key Testname: CH 11 1) TRUE 2) FALSE 3) TRUE 4) TRUE 5) TRUE 6) B 7) A 8) E 9) D 10) B 11) A 12) C 13) dust 14) scattering 15) open cluster 16) Gas is almost all hydrogen and helium, but the dust is clumps of heavier elements, condensed out as grains much like the material of the Earth. 17) From the release of gravitational energy as the protostar shrinks in stages 2 and 3. 18) A protostar of insufficient mass (less than 8% of the Sun's mass) that does not get hot enough from gravitational contraction to reach 10 million degrees and reach stage 7 as a stable main sequence star. 19) The higher the mass, the greater its gravity, so the faster it shrinks and heats up to reach the main sequence. Once there, it will fall to the top left of the H-R diagram, and as a spendthrift star, rapidly deplete its supply of hydrogen and leave the main sequence, evolving into a red giant such as those that dominate the globular clusters. 20) 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. 3.