Stellar Astronomy Sample Questions for Exam 4

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1 Stellar Astronomy Sample Questions for Exam 4 Chapter Emission nebulas emit light because a) they absorb high energy radiation (mostly UV) from nearby bright hot stars and re-emit it in visible wavelengths. b) they are burning hydrogen and helium gas. c) they are gravitationally collapsing and are thus heating up. d) emission nebula is a misnomer, they do not emit at all. 2. Interstellar reddening is due to a) light with blue wavelengths scattering more efficiently off small interstellar dust particles than red wavelengths. b) light with red wavelengths scattering more efficiently off small interstellar dust particles than blue wavelengths. c) the gas in interstellar space emitting red wavelengths. d) the gas in interstellar space absorbing blue wavelengths. 3. The most common gas found in interstellar space is a) oxygen. b) nitrogen. c) hydrogen. d) helium. 4. An H II region is a) a region of heavy atoms and molecules in the core of stars. b) a region of neutral hydrogen in a giant molecular cloud. c) a region of ionized hydrogen gas near very hot stars. d) the core of a protostar where hydrogen is almost ready to burn. 5. Stars are formed in a) deep space that is free of all dust and gas. b) cold dark clouds of gas and dust. c) deep space that contains hot ionized gas. d) in the cores of red supergiants. 6. The path a contracting low mass protostar on an H-R diagram a) first moves horizontally right to left then straight downward. b) first moves horizontally left to right then moves straight up. c) first moves almost straight down then horizontally right to left. d) first moves almost straight up then horizontally right to left.

2 7. A Bok globule is a) a hot pocket of low density gas on the surface of a red supergiant. b) a pocket of cold dense gas and dust where a protostar is forming. c) a glowing region of ionized hydrogen. d) a giant cloud of gas and dust that can be a thousand lightyears across 8. A protostar is formed by a) the rapid expansion of gas from an exploding star. b) the gravitational collapse of a rotating interstellar cloud. c) the ignition of thermonuclear fusion in an expanding nebula. d) the remnants of a red giant star. 9. Giant molecular clouds are composed of a) mostly carbon molecules with traces of hydrogen and helium. b) mostly interstellar dust and organic molecules. c) mostly molecular hydrogen and helium with small amounts of complex carbon compounds and other heavy elements and compounds. d) exclusively hydrogen molecules and nothing else. 10. Giant molecular clouds are a) giant clouds of ionized hydrogen and multiply ionized atoms. b) giant clouds of mostly water vapor and ice crystals. c) giant clouds of hot hydrogen, helium and other heavy elements. d) giant clouds of cold gas and dust where stars are born. 11. Bipolar outflows are a) low speed gas flows passing through the equatorial planes of old stars. b) high speed gas flows out the polar axis of protostars. c) beams of gamma and x-rays shooting out the polar axis of neutron stars. d) high speed gas flows into a collapsing molecular cloud. 12. Herbig-Haro objects are a) old stars near the end of their life. b) young stars that form jets shooting out along their polar axis. c) middle aged stars that have planetary systems in orbit around them. d) young stars that are fairly quiescent and are still shrouded in a cocoon of gas and dust. Short Answer Questions 1. Describe the formation of a star from a clump of gas and dust in a GMC through the protostar stage and finally to a full fledged star. 2. Describe some of the observational evidence we have which support the theories for the formation of stars in GMC s.

3 3. Describe a Herbig-Haro object. What does it look like? Why does it look like it does? What kind of star is involved with a HH object? 4. How can a star end up with only a small fraction of the mass that was contained in the original clump of gas and dust it formed from? Describe some of the mechanisms of mass loss in protostars and newborn high-mass stars. Chapter Main sequence stars are a) stars whose mass is less than 5 solar masses. b) stars of all masses which are burning hydrogen in their core. c) stars whose mass is greater than 5 solar masses. d) stars which are more luminous than the Sun. e) stars which are less luminous than the Sun. 2. A Zero-age main sequence star is a) the same size it will be late in its life on the main sequence. b) much larger than it will be late in its life on the main sequence. c) smaller than it will be late in its life on the main sequence. d) a star that is very near the end of its life. 3. In general, the more massive the star a) the smaller it will be. b) the cooler it will burn. c) the shorter it will live. d) the farther away it is. 4. Which of the following stars will have the longest life? a) A two solar mass star. b) A 0.5 solar mass star. c) A 50 solar mass star. d) A 10 solar mass star. 5. When a one solar mass star burns up all the hydrogen in its core a) the core expands and cools while the outer region of the star contracts and heats up. b) it immediately starts burning helium in the core. c) it explodes in a supernova. d) the core contracts and heats up while the outer region of the star expands and cools to become a red giant. 6. Degenerate matter has the property that a) all the lowest electron energy levels are filled. b) the more mass that is added, the smaller the object becomes in size. c) the density of the matter is extremely high.

4 d) the temperature is the same everywhere because it is such a good heat conductor. e) All of the above. 7. A star moves off the main sequence when a) helium fusion begins. b) hydrogen fusion in the core ends. c) nuclear reactions begin. d) carbon fusion begins. e) None of the above, stars are always on the main sequence. 8. To burn helium by the triple alpha process in the core of a star requires a temperature of at least a) 20 million Kelvin. b) 100 million Kelvin. c) 1 billion Kelvin. d) 1 million Kelvin. 9. When a one solar mass star has burned all the helium in its core a) it collapses into a black hole. b) it blows off its outer layers to form a planetary nebula and becomes a white dwarf. c) it explodes in a supernova and leaves nothing behind. d) it begins burning carbon in its core. 10. When a one solar mass star dies, it leaves a corpse that is a) a spinning neutron star. b) a black hole. c) a brown dwarf. d) a white dwarf. 11. A planetary nebula is a) the expanding shell of gas from a Type II supernova. b) the expanding shell of gas from a Type Ia supernova. c) the expanding shell of gas thrown off during the last stages of life of a low mass star (core mass less than 1.4 solar masses). d) the material from planets that are destroyed during a Type II supernova.

5 12. A planetary nebula is formed when a) a massive star explodes in a supernova. b) a GMC contracts to form a protostar. c) a brown dwarf star stops fusing hydrogen into helium. d) a star like our sun reaches the end of its life. 13. The Chandrasekhar limit is a) the maximum mass of a white dwarf star. b) the minimum mass of a white dwarf star. c) the maximum mass of a neutron star. d) the maximum mass of a black hole. 14. A white dwarf star is composed of a) pure neutrons. b) elements heavier than iron. c) a degenerate electron gas of mostly carbon and oxygen. d) a degenerate electron gas of hydrogen. 15. If a star is born with a mass 4 times the mass of the Sun, when it becomes a white dwarf its mass is a) just barely less than 4 solar masses. b) exactly the same. c) greater than 4 solar masses. d) much less than 4 solar masses. 16. When two stars orbit very close to each other a) mass can be transferred from one star to the other through the Lagrange point. b) the smaller star always gets completely swallowed by the larger star. c) the two stars exchange mass until they are both the same size and then their evolutionary tracks become parallel. d) the two stars always eventually collide and explode in a gamma ray burster. 17. A Type Ia supernova occurs for a) a black hole. b) a low mass red dwarf. c) a star on the main sequence. d) a white dwarf in a binary system.

6 Short Answer Questions 1. Describe the lifecycle of a one solar mass star from ZAMS to the end of helium burning 2. Discuss how an H-R diagram of a cluster can be used to determine the age of the cluster. 3. Describe some of the difference between regular matter and degenerate matter. 4. Describe the formation and evolution of a planetary nebula from the ABG stage to a lone white dwarf star. 5. Describe a white dwarf star. What is it composed of? How big is it? How does its size depend on its mass? How does it evolve? 6. Briefly describe how stars in a binary system can exchange mass. How is it possible for a binary system to have a main sequence star more massive than its more evolved companion? 7. Describe a Type I supernova. What kind of star does it occur for, what is the difference between it and an ordinary nova, what is left behind after the supernova? 8. What is the Chandrasekhar Limit? What kind of matter does it apply to? What happens if something exceeds it? Chapter When a massive star (core mass >1.4 solar masses) nears the end of its life a) the core is composed of a degenerate electron gas of helium. b) the core continues to burn hydrogen to the very end. c) the core is composed of super heavy elements heavier than uranium. d) the core becomes layered with iron in the center and layers of silicon, oxygen, carbon and helium as you move outward. 2. In a supernova, the process of combining electrons and protons to form neutrons is called a) electron liberation. b) neutrino decay. c) neutron capture. d) reverse beta decay. 3. A Type II supernova occurs for a) a lone white dwarf. b) a black hole. c) a low mass red dwarf. d) a massive red or blue supergiant.

7 4. Elements heavier than iron are produced a) in the core of red dwarf stars on the main sequence. b) in the core of white dwarf stars. c) during supernovas. d) in the core of stars like our sun on the main sequence. 5. In a Type II supernova, most of the energy is carried away by a) the neutrinos produced when the electrons and protons in the core add to form neutrons. b) the expanding shell of gas that was the outermost layers of the star. c) the neutrons produced in the initial collapse. d) the electrons that are blown outward by the initial explosion. 6. A supernova remnant is a) the expanding shell of gas thrown off during the last stages of life of a low mass star (core mass less than 1.4 solar masses). b) the material from planets that are destroyed during a Type II supernova. c) the expanding shell of debris from a supernova (Type Ia, Ib, Ic or II). d) the spinning neutron star left behind after a Type Ib, Ic or II supernova. 7. A neutron star is composed of a) a degenerate electron gas of carbon. b) a degenerate electron gas of helium. c) a degenerate neutron gas. d) a degenerate proton gas. 8. A pulsar is a a) slowly rotating black hole. b) rapidly rotating neutron star. c) a dying white dwarf. d) a new born star (a ZAMS). 9. The maximum mass of a neutron star is a) about 2 3 solar masses. b) 1.4 solar masses. c) about 10 solar masses. d) less than 0.5 solar masses. e) None of the above, there is no limit to the mass of a neutron star. 10. The magnetic field of a new neutron star is a) about the same strength as the average field on the Sun. b) about the same as the average field on the Earth. c) about the same as the field in a sunspot. d) about a trillion times the strength of the average field on the Sun.

8 11. An isolated pulsar spins down because a) the pulsar radiates energy which comes out of the spin of the star. b) the pulsar is being slowed by matter falling onto its surface. c) the pulsar is being slowed by collisions with other neutron stars. d) Isolated pulsars do not spin down, they spin-up (rotate faster). 12. A pulsar pulses because a) the star is undergoing rapid increases and decreases in its surface temperature and diameter. b) the fusion process at the surface of the star is turning on and off at a rapid rate. c) the light from the star is being emitted from the magnetic poles of the star that are rotating around at a rapid rate. d) the light from the star is turning on and off at a rapid rate for some unknown reason. 13. The density of matter in a neutron star is a) about the same as the density of lead on the Earth. b) about the same as the density of matter in a white dwarf star. c) less than the density of normal matter on the Earth. d) about one hundred trillion times the density of water on Earth. 14. An x-ray burster is a) a blast of x-rays coming from the collapse of a white dwarf star that exceeds the Chandrasekhar limit. b) a blast of x-rays coming from a helium flash occurring at the surface of a neutron star. c) a blast of x-rays coming from a hydrogen flash occurring at the surface of a white dwarf star. d) a blast of x-rays coming from the collapse of a neutron star that exceeds its mass limit. 15. The H-R diagram of a very young stellar cluster will have a) stars scattered all over the graph. b) only main sequence stars of low mass and a few white dwarfs. c) main sequence stars up to 4 or 5 solar masses along with red giants and white dwarfs. d) main sequence stars of all masses, protostars still evolving towards the main sequence and very few of any other types.

9 16. The H-R diagram of a very old stellar cluster will have a) only low mass main sequence stars with a solar mass or less, a few red giants and lots of white dwarf stars. b) stars scattered all over the graph with a large number of supergiants and white dwarfs as well as main sequence stars of all mass. c) main sequence stars up to 4 or 5 solar masses along with red giants and white dwarfs. d) main sequence stars of all masses and very few of any other types. Short Answer Questions 1. Describe the CNO cycle. What is different about it and the proton-proton cycle? Why do only high mass stars burn hydrogen this way and not low mass stars? 2. Describe a Cepheid variable star. Why are these types of stars important to determining distances in astronomy? What kinds of stars are they? 3. Describe the sequence of events in a Type II supernova beginning with an onion-layered core through the formation of a pulsar. 4. Describe the lighthouse model of a pulsar. Why does it pulse, what causes it to radiate, what are the typical periods of the pulses and how long do the pulses last? 5. Describe an X-ray binary. Why is it creating x-rays? What type of system does it occur in? 6. Describe how an HR diagram of a cluster can be used to determine its age. Why is it important to observe lots of different clusters and do HR diagrams of them? What do we learn by observing a wide range of clusters?

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