Universe Tenth Edition Chapter 18 The Birth of Stars Roger Freedman Robert Geller William Kaufmann III Clicker Questions We see an emission nebula via A.reflected blue light from a nearby star. B.reflected red light from a nearby star. C.blue light emitted by hot (excited) hydrogen atoms. D.red light emitted by hot (excited) hydrogen atoms. E.x-rays emitted by hot (excited) hydrogen atoms. Q18.1 We see an emission nebula via A.reflected blue light from a nearby star. B.reflected red light from a nearby star. C.blue light emitted by hot (excited) hydrogen atoms. D.red light emitted by hot (excited) hydrogen atoms. E.x-rays emitted by hot (excited) hydrogen atoms. A18.1 The Orion nebula is A.a reflection nebula illuminated by newly formed stars. B.an emission nebula heated by newly formed stars. C.a supernova remnant. D.an emission nebula heated by a supernova remnant. E.a dark nebula composed of dust. Q18.2 The Orion nebula is A.a reflection nebula illuminated by newly formed stars. B.an emission nebula heated by newly formed stars. C.a supernova remnant. D.an emission nebula heated by a supernova remnant. E.a dark nebula composed of dust. A18.2 The dark regions in this photo of the Trifid nebula are caused by A.hot hydrogen gas. B.cold hydrogen gas. C.dust and cold gas obscuring the light. D.a supernova remnant. E.dark matter. Q18.3 The dark regions in this photo of the Trifid nebula are caused by A.hot hydrogen gas. B.cold hydrogen gas. C.dust and cold gas obscuring the light. D.a supernova remnant. E.dark matter. A18.3 The bright red regions in this photo of the Trifid nebula are caused by A.hot hydrogen gas. B.cold hydrogen gas. C.dust and cold gas obscuring the light. D.a supernova remnant. E.dark matter. Q18.4 The bright red regions in this photo of the Trifid nebula are caused by A.hot hydrogen gas. B.cold hydrogen gas. C.dust and cold gas obscuring the light. D.a supernova remnant. E.dark matter. A18.4 Astronomers discover an object that emits most of its electromagnetic radiation at infrared wavelengths. What could this object be? A.A protostar B.A main-sequence star of spectral class G C.A supergiant star of spectral class G D.A main-sequence star of spectral class B E.More than one of the above Q18.5 Astronomers discover an object that emits most of its electromagnetic radiation at infrared wavelengths. What could this object be? A.A protostar B.A main-sequence star of spectral class G C.A supergiant star of spectral class G D.A main-sequence star of spectral class B E.More than one of the above A18.5 Which of the following are thought to be mechanisms that can cause a giant molecular cloud to collapse and form a protostar? A.The shock wave from a nearby supernova B.The shockwave from a newly formed high-mass star that is nearby C.The shockwave experienced by the cloud as it passes through a spiral arm D.All of the above E.None of the above Q18.6 Which of the following are thought to be mechanisms that can cause a giant molecular cloud to collapse and form a protostar? A.The shock wave from a nearby supernova B.The shockwave from a newly formed high-mass star that is nearby C.The shockwave experienced by the cloud as it passes through a spiral arm D.All of the above E.None of the above A18.6 High-mass protostars evolve into main-sequence stars A.more quickly than low-mass protostars because their stronger gravity speeds up their collapse. B.more quickly than low-mass protostars because their higher core temperature speeds up their collapse. C.more slowly than low-mass protostars because their stronger gravity slows their collapse. D.more slowly than low-mass protostars because their higher core temperature slows their collapse. E.at the same rate as low-mass protostars. Q18.7 High-mass protostars evolve into main-sequence stars A.more quickly than low-mass protostars because their stronger gravity speeds up their collapse. B.more quickly than low-mass protostars because their higher core temperature speeds up their collapse. C.more slowly than low-mass protostars because their stronger gravity slows their collapse. D.more slowly than low-mass protostars because their higher core temperature slows their collapse. E.at the same rate as low-mass protostars. A18.7 What happens when a protostar joins the main sequence? A.Its surface area increases significantly. B.Its luminosity increases significantly. C.Its luminosity and surface area both increase significantly. D.Nuclear fusion begins in its core. E.Nuclear fission begins in its core. Q18.8 What happens when a protostar joins the main sequence? A.Its surface area increases significantly. B.Its luminosity increases significantly. C.Its luminosity and surface area both increase significantly. D.Nuclear fusion begins in its core. E.Nuclear fission begins in its core. A18.8 Main-sequence stars have masses greater than about 0.08 solar masses. The reason for this is that gas clouds smaller than 0.08 solar masses A.do not develop the necessary high temperature and pressure required for nuclear fusion when they collapse. B.are too small to begin to collapse. C.generate enough energy that they fragment into smaller mass objects when they collapse. D.become white dwarf stars. E.do not exist as far as we know. Q18.9 Main-sequence stars have masses greater than about 0.08 solar masses. The reason for this is that gas clouds smaller than 0.08 solar masses A.do not develop the necessary high temperature and pressure required for nuclear fusion when they collapse. B.are too small to begin to collapse. C.generate enough energy that they fragment into smaller mass objects when they collapse. D.become white dwarf stars. E.do not exist as far as we know. A18.9 Why do protostars eventually stop their gravitational collapse? A.Their core temperature becomes high enough that nuclear fusion starts. This causes high pressure in the inner layers of the star, which halts the collapse. B.All the gravitational energy is used up. C.The strong (nuclear) force stops any further collapse when the atoms get too close together. D.The high pressure generated by the weight of the surface layers forces the interior to become solid and rigid. Q18.10 Why do protostars eventually stop their gravitational collapse? A.Their core temperature becomes high enough that nuclear fusion starts. This causes high pressure in the inner layers of the star, which halts the collapse. B.All the gravitational energy is used up. C.The strong (nuclear) force stops any further collapse when the atoms get too close together. D.The high pressure generated by the weight of the surface layers forces the interior to become solid and rigid. A18.10 This H-R diagram of the Pleiades indicates that this star cluster is A.so young that most of its cool, low- mass stars have not yet arrived at the main sequence. B.so young that most of its hot, low- mass stars have not yet arrived at the main sequence. C.old enough that all of its cool, low- mass stars have arrived at the main sequence. D.old enough that all of its cool, high- mass stars have arrived at the main sequence. E.None of these options is correct. Q18.11 This H-R diagram of the Pleiades indicates that this star cluster is A.so young that most of its cool, low- mass stars have not yet arrived at the main sequence. B.so young that most of its hot, low- mass stars have not yet arrived at the main sequence. C.old enough that all of its cool, low- mass stars have arrived at the main sequence. D.old enough that all of its cool, high- mass stars have arrived at the main sequence. E.None of these options is correct. A18.11