Physics130 Astronomy Exam #3 November 19, 2004

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1 Physics130 Astronomy Exam #3 November 19, 2004 Name 1. The star that is seen at the center of a planetary nebula is a.) a planet in the process of formation. b.) A small, hot, and dense, white dwarf star. c.) The accretion disk around a black hole. d.) Composed almost entirely of neutrons, and is spinning rapidly. 2. How does a white dwarf generate its energy? a.) Nuclear fusion of hydrogen into helium is producing energy within its core. b.) Nuclear fussion of heavy elements in the central core is releasing energy. c.) It no longer generates energy, but is slowly cooling as it radiates away its heat. d.) Gravitational potential energy is released as the star slowly contracts. 3. A pulsar is most probably formed a.) at the center of a supernova explosion. b.) in the high-temperature core of a star as it evolves through its main sequence phase. c.) just after the formation of a protostar by gravitational condensation. d.) Within a huge gas cloud, by the collision between stars. 4. Which of the following statements is NOT a property of neutron stars? a.) They are composed almost entirely of neutrons b.) They emit relatively narrow beams of light and other radiation. c.) They contain weak gravitational fields. d.) They rotate from about one to thirty times each second. 5. What prevents a neutron star from collapsing and becoming a black hole? a.) Gravity in the neutron star is balanced by an outward force due to neutron degeneracy. b.) Neutron stars are held up by the centrifugal force due to their rapid rotation. c.) Gravity in a neutron star is balanced by an outward force due to ideal gas pressure, as in the sun. d.) Neutron stars are solid, and like any solid sphere are held up by the repulsive force between atoms in a solid. 6. The escape velocity of matter from near the center of a black hole whose mass is 3 solar masses is a.) quite small. b.) about half the speed of light. c.) much greater than the speed of light. d.) always exactly equal to the speed of light. 1

2 7. Which effects have been useful in the search for black holes in the universe? a.) Their gravitational influence on nearby matter, particularly companion stars. b.) Their magnetic fields and the influence of these fields on nearby matter. c.) The effect of their angular momentum or spin on nearby matter. d.) The influence of their intense gravitational field on atoms that are emitting light from the event horizons of the black holes. 8. Cepheid stars are useful to astronomers as indicators of a.) the existence of black holes. b.) distance, particularly to nearby galaxies. c.) white dwarf star behavior. d.) Stars with very high speed motion. 9. Galaxies throughout the Universe appear to be distributed a.) mostly in a single spherical shell surrounding a void in space, presumed to have been caused by a vast explosion. b.) uniformly throughout space. c.) In groups and surfaces surrounding vast voids, much like the surfaces of giant bubbles. d.) Around a single point in space, the presumed location of the original Big Bang, which created the Universe. 10. The one component of the material of the Milky Way Galaxy that prevents us from seeing and photographing the galactic center at optical wavelengths is a.) very cold hydrogen gas. b.) interstellar dust. c.) the glare of light from nearby stars. d.) hot hydrogen gas. 11. The Milky Way is an example of which type of galaxy? a.) Elliptical b.) Spiral c.) Irregular d.) L enticular, SO type 12. Which components of our Galaxy best outline the spiral arms? a.) Young O and B type stars. b.) Globular clusters. c.) Predominantly solar-type stars. d.) White dwarfs. 2

3 13. Which two parameters of star motion in the Milky Way are represented by its rotation curve? a.) Orbital period of the stars as a function of their distance from the galactic center. b.) Star position above or below the galactic plane a function of distance from the galactic center. c.) Orbital speed as a function of star distance from the galactic center. d.) Orbital speed of the stars as a function of their individual masses. 14. Much of the mass of our Galaxy appears to be in the form of dark matter of unknown composition. At present, this matter can be detected because a.) its gravitational pull affects orbital motions in the Galaxy b.) it blocks out the light from distant stars in the plane of our Galaxy. c.) It bends light from distant quasars d.) It emits synchrotron radiation of radio wavelengths. 15. What is the Hubble classification for a spiral galaxy with a small nuclear region and loosely wound arms? a.) Sc b.) Sb c.) Sba d.) Sa 16. Why is it strange to find spiral arms in spiral galaxies? a.) spiral arms require new stars, and previous new stars should have already used up all of the interstellar medium; no new stars should be forming now. b.) There is no known mechanism to generate spiral arms. c.) Their motion and differential rotation should have wound up their arms and made them blend and disappear. d.) Galaxies are not rotating fast enough to form the observed spiral arms. 17. According to the Hubble classification scheme, an E4 galaxy has a.) a disk and central bulge, with a smooth light distribution and no spiral arms. b.) A round or spherical shape with a smooth light distribution and no disk or central bulge. c.) An elliptical shape (flattened circle) with a smooth light distribution. d.) An irregular shape. 18. There is little or no interstellar dust or gas in which of the following galaxy types? a.) Spirals b.) Barred spirals c.) Ellipticals d.) Irregular 3

4 19. The Local Group is a.) a cluster of galaxies in which the Milky Way is located. b.) The family of planets around the Sun. c.) The name of the spiral arm of our Galaxy in which the sun is located. d.) A star cluster to which the sun belongs. 20. The Hubble relation links which two characteristics of distant objects in the Universe? a.) Stellar mass and luminosity. b.) State of organization and age of clusters of stars. c.) Distance and velocity of recession. d.) Luminosity and surface temperature. 21. What method is used to determine the distances of very remote galaxies? a.) Measurement of the angular size of the galaxy and an assumption about the actual physical size of the galaxy? b.) Comparison of their apparent and absolute magnitudes. c.) Measurement of the apparent brightness and period of Cepheid variable stars within the galaxies. d.) Use of their spectral redshifts and the Hubble law. 22. to an astronomer, what is a standard candle? a.) Any type of object whose absolute magnitude is known. b.) A standard light source that is placed in a telescope, to which the brightness of stars and other objects can be compared. c.) An accurately defined brightness scale for stars and galaxies, such as the magnitude scale. d.) Any galaxy whose red shift has been measured accurately. 23. Which of the following objects are NOT used as standard candles for distance measurement to distant galaxies? a.) Cepheid variable stars. b.) Globular clusters. c.) Supernova explosions d.) Hot white dwarf stars. 24. Quasars all appear to be a.) moving towards us at high speeds, as high as 90% of the speed of light. b.) moving across our line of sight at very high speeds, as seen from time-lapse photographs. c.) moving away from us at very high speeds, at up to 90% of the speed of light. d.) extremely massive objects in our galaxy, their intense surface gravity having redshifted their spectra. 4

5 25. The emission lines in quasar spectra were difficult to identify initially because a.) they appeared to be created by elements which did not exist on Earth. b.) no one expected violet and ultraviolet spectral lines to be shifted so far toward the red. c.) they were very faint and could not be measured accurately. d.) emission lines of such intensity were not expect from astronomical sources. 26. Evidence obtained over the last few years indicates that quasars are a.) the remnant cores of exploding stars or supernovae. b.) evidence of very intense star-building activity in certain distant dust and gas clouds. c.) the focused image of a distant galaxy by the gravitational lens effect of a closer galaxy. d.) the central nuclei of very distant, very active galaxies. 27. Sychrotron radiation is produced whenever a.) electrons jump from level to level in an atom. b.) electrons are accelerated as they circle in spirals in a magnetic field. c.) electrons move in a transparent medium at a speed faster than the speed of light in that material. d.) atoms in a molecule vibrate back and forth. 28. In relation to the universe, what does isotropy mean? a.) The expansion is the same in all directions. b.) The speed of expansion is the same at all distances. c.) The speed of expansion at any given distance is the same at all times. d.) The universe is the same everywhere, neither expanding nor contracting. 29. What major problem would arise if the value of Hubble s constant turned out to be 100 km/s/mpc? a.) Galaxies would be traveling too fast for the universe to be gravitationally bound. b.) Galaxies would be traveling faster than observations allow. c.) The age of the universe would be less than the ages of some of the stars in it. d.) Some galaxies would be farther away than the edge of the universe. 5

6 30. Which single observation is perhaps the strongest argument against the steadystate model of the universe, and for the Big Bang model? a.) The universe is bathed in a sea of microwaves coming from the edge of the visible universe. b.) The number of supporters of the steady-state model is less than the number of supporters of the Big Bang model. c.) The universe is expanding. d.) We have not observed matter being created from nothing in the space around us. 31. Which of the four fundamental forces holds the electrons in the atom? a.) The gravitational force. b.) The strong nuclear force. c.) The electromagnetic force. d.) The weak nuclear force. 32. What are the particles that make up protons and neutrons? a.) Quarks b.) Neutrinos c.) Muons d.) Gravitons 33. When two gamma ray photons undergo pair production, What are the final final products? a.) an electron and a positron (the antielectron) b.) An electron and an antineutrino c.) A proton, an electron, and an antineutrino d.) Two x-ray photons, each with half the energy of the gamma rays. 34. When did the universe cool to a temperature of 3K? a.) About 1 million years after the Big Bang, when the universe became transparent to radiation. b.) 1 second after the start of the Big Bang, when pair production ceased. c.) 3 minutes after the start of the Big Bang, when primordial nuclear reactions ceased. d.) Very recently. 6

7 35. Why would we expect the rate of expansion of the universe to be slowing down? a.) The greater the distance between two objects (such as galaxies or superdusters), the harder it is to push them further apart. b.) Galaxies feel a kind of friction as they move through space, and this slows them down. c.) The gravitational pull of all objects in the universe on each would lead to a slow down. d.) All expansions after explosions just naturally slow down with time. 36. What condition is necessary for the universe to be unbounded (infinite in extent)? a.) The density of the universe must be greater than some critical value. b.) The density of the universe must be equal to some critical value. c.) The density of the universe must be equal to or less than some critical value. d.) The universe must have no mass in it. 37. What will happen if the universe is bounded? a.) The universe will expand past its maximum size, then fragment into miniuniverses. b.) The universe will eventually fall back in on itself, heading toward a Big Crunch. c.) The universe will reach a maximum size and remain there, like a balloon being blown up. d.) The universe will expand forever. 38. What kind of curvature (geometry of space) does the universe have if the universe is just bounded (or just unbounded, i.le., exactly critical density)? a.) Flat b.) Parabolic c.) Spherical d.) Hyperbolic. 7

8 TRUE OR FALSE: 39. The sun will eventually become a neutron star. 40. Degenerate gases are similar to normal (ideal) gases in that they expand when heated. 41. A white dwarf star more massive than 1.4 solar masses cannot exist. 42. A white dwarf that increases in mass will shrink in radius. 43. At a black hole singularity, density and pressure become zero. 44. The sun appears red at sunset because the blue light has been scattered away by the Earth s atmosphere. 45. The sun is a Population I star. 46. Globular clusters are Population II objects. 47. A spiral galaxy is usually at the center of rich clusters of galaxies. 48. The observed expansion of the universe proves that the Milky Way is at the. center of the universe. 49. The Hubble constant is directly related to the age of the universe. 50. The temperature of the 3K background radiation is 10K. 8

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