Stellar Astronomy Sample Questions for Exam 5

Transcription

1 Stellar Astronomy Sample Questions for Exam 5 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 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. 2. 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. 3. 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. 4. 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. 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.

4 6. 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. 7. 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. 8. 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. 9. 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. 10. 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. 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.

5 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. 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.

6 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.

7 11. 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. 12. 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. 13. 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). 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. 16. The Equivalence Principle state a) Mass and energy are equivalent. b) The speed of light is the speed limit of the universe. c) You cannot distinguish between an acceleration and gravity. d) It is impossible to determine who is moving and who is stationary.

8 17. 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. 18. One of the basic principles of Einstein s Special Relativity is a) The speed of light depends on the relative speed between the source and the observer. b) It is always possible determine who is moving and who is stationary. c) The observed laws of physics are the same regardless of any constant velocity at which you move. d) It is possible to move at speeds greater than the speed of light. 19. If an observer is stationary on the surface of the Earth and watches a spacecraft moving past at 9 /10 the speed of light he sees a) simultaneous flashes on the spacecraft appear simultaneous to both him and the person on the spacecraft b) the stationary observer sees the moving clock as running fast. c) the stationary observer sees the moving length as long. d) the stationary observer sees the moving clock as running slow. 20. General Relativity is a) a theory that explains what happens when objects move at speeds close to the speed of light. b) a theory that explains the internal structure of the atom. c) a theory that explains how mass effects the shape of spacetime. d) a process of tracing ones relatives back to ancient times. 21. If one atomic clock is at sea level and another is placed on top of Mount Everest, which of the following is true? a) The clock on Mount Everest runs slower than the one at sea level. b) The clock at sea level runs slower than the one on Mount Everest. c) Both clocks keep exactly the same time. d) The clock on Mount Everest will stop because of the high altitude. 22. Gravitational redshift is a) the cause of red skies at sunset and sunrise. b) the reason supergiant stars are usually red in color. c) the stretching of the wavelength of light due to the source moving away from the observer. d) the stretching of the wavelength of light due to an intense gravitational field.

9 23. The event horizon of a black hole is a) the point where the escape velocity equals the speed of light for a black hole. b) the instant in time when the star collapses into a black hole. c) the size of the star before it collapses into a black hole. d) the curvature of space near a black hole. 24. Matter falling into a black hole emits in x-rays because a) it is heated to very high temperatures by friction due to the very high velocities it is accelerated to. b) it is passing through regions of space where time is slowed down due to the extreme curvature of space-time. c) the black hole is emitting in gamma rays which are absorbed by the matter and then re-emitted in x-rays. d) the matter is annihilated as it crosses the event horizon of the black hole. 25. The point of no escape from a non-rotating black hole is a) the Schwarzschild radius of the black hole. b) the singularity of the black hole. c) 10 AU from the singularity of the black hole. d) 1 AU from the singularity of the black hole. Short Answer Questions 1. Describe the sequence of events in a Type II supernova beginning with an onion-layered core through the formation of a pulsar. 2. 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? 3. Describe an X-ray burster. Why is it creating x-rays? Why is it bursting? What type of system does it occur in? 4. Briefly discuss Einstein s General Theory of Relativity. What is the difference between General Relativity and Special Relativity? What is the basic principle of General Relativity? What are some of the consequences of General Relativity? 5. Describe a black hole and under what conditions it is possible to see a black hole. Chapter The person(s) most responsible for developing the galaxy classification scheme we still use was a) Albert Einstein. b) Ejnar Hertzsprung and Henry Norris Russell. c) Edwin Hubble. d) Harlow Shapley.

10 2. The three types of galaxies are a) spiral, elliptical and irregular. b) small, medium and large. c) round, square and triangular. 3. Most elliptical galaxies contain a) stars of all ages with lots of gas and dust. b) mostly young stars and lots of gas but no dust. c) mostly old stars and lots of dust but no gas. d) mostly old stars, very little gas and almost no dust. 4. An SBa galaxy is a) a barred spiral with a large nucleus and tightly wound arms. b) a barred spiral with a small nucleus and loosely wound arms. c) a plain spiral with a small nucleus and loosely wound arms. d) a giant elliptical that is only slightly out of round. 5. Most irregular galaxies have unusual shapes because a) they are exploding because of the quasar located in their center. b) they have been involved in galactic collisions. c) they evolved that way in isolation. d) they are being pulled apart by dark matter. 6. Studies of the orbital velocity of stars in spiral galaxies reveals a) most of the mass is visible mass that is located in their nuclear bulge. b) most of the mass is visible mass that is located in the disk of galaxies. c) most of the mass is dark matter located in a spherical halo around the galaxies d) most of the mass is in the supermassive black hole at the center of the galaxies. 7. Most of the dark matter in the spiral galaxies is a) black holes of stellar mass located in the halo. b) old, non-rotating neutron stars located in the halo. c) cold gas and dust located in the halo. d) protostars not yet undergoing fusion located in the halo. e) None or all of the above, we don t know what dark matter is. 8. The spiral arms of galaxies a) rotate like a solid disk. b) are caused by the winding up of the stars since they all have roughly the same orbital speed. c) are a density wave that travels around the galaxy at a slower speed than the stars. d) are only a temporary feature that will disappear completely in a few thousand years.

11 9. Collisions between galaxies are a) rare events that have never been observed. b) very common events that are important in the formation of galaxies. c) catastrophic events that result in numerous collisions between stars and the destruction of all galaxies involved. d) gentle events in which the galaxies simply pass through each other unscathed by the collision. 10. Quasars are a) extremely luminous objects located very far away due to their large redshift. b) very luminous objects located in the solar system. c) very luminous objects located in the Milky Way galaxy. d) very luminous objects located in nearby galaxies. 11. The size of a quasar is a) about the size of the Earth. b) about the size of the solar system. c) about the size of the Milky Way galaxy. d) billions of lightyears across. 12. The brightness of some quasars can vary significantly in a) milliseconds. b) a few seconds to a few minutes. c) a few hours. d) a few weeks to a few months. 13. Galaxies with AGN are a) galaxies with no nucleus. b) galaxies with active nuclei. c) galaxies with no activity in their nuclei. d) exploding galaxies. 14. Radio lobes are a) radio transmitters you attach to your ear lobes. b) gas and dust in intergalactic space that emit in radio waves due to jets of materials being shot into them from nearby galaxies. c) red giant stars that emit radio waves along their equator. d) stars that act as radio receivers. 15. The central energy source of an AGN is a) a multimillion solar mass neutron star. b) a multimillion solar mass globular cluster. c) a multimillion solar mass black hole. d) a megastar of several hundred solar masses.

12 Short Answer Questions 1. Discuss the density wave theory of the spiral arms of the galaxy. How does the theory lead to the formation and perpetuation of spiral arms in a galaxy? How does the theory explain the winding dilemma? 2. Briefly describe the galaxy classification scheme. Discuss the differences between S, SB, E and Ir galaxies as well as the difference between Sa, Sb and Sc galaxies and the different types of E galaxies. 3. Describe a typical quasar: its luminosity, redshift, spectra, distance away and variability. 4. Describe the process that creates radio lobes. Where does the energy to power them come from, how big are they, around what kind of objects are they observed. 5. Describe the similarities between quasars, blazers and Seyfert galaxies. What are the differences between them? What is the source of power for all of them?