Galaxies and Cosmology Review Game Questions. 2. Approximately how far is the Sun from the center of our galaxy?

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1 Galaxies and Cosmology Review Game Questions 1. Cepheid stars are useful to astronomers as indicators of. 2. Approximately how far is the Sun from the center of our galaxy? 3. What are the dimensions of the disk of our Milky Way galaxy? 4. Where in space would you look for a globular cluster? 5. Where in the Milky Way would you expect most star formation to be taking place? 6. The Milky Way is an example of which type of galaxy? 7. The possible presence of a very large amount of unseen ( dark ) matter in the halo of our galaxy is deduced from 8. Since dark matter cannot be seen, how can we detect its presence? 9. What type of object has been proposed to explain the tremendous activity detected at the center of our galaxy? 10. What evidence now exists for a supermassive black hole at the center of our galaxy? 11. How has the presence of a supermassive black hole at the center of our galaxy been deduced? 12. How did Hubble determine the distance to the Andromeda Galaxy (M31)? 13. The Milky Way is an example of which type of galaxy? 14. What is the basic shape of a spiral galaxy? 15. Which type of galaxy contains little or no interstellar dust or gas? 16. An elliptical galaxy contains mostly what kind of stars? 17. Describe the primary evidence for the Expanding Universe concept. 18. What is the Local Group? 19. Which types of galaxies are most spherical in shape? 20. What does Hubble s law state? 21. Describe how galaxies are distributed through the universe. 22. What evidence is there for considerable extra mass within galaxies which does not produce visible light the so-called dark matter? Page 1

2 23. Describe the characteristics of a quasar. 24. The fact that quasars can be detected from distances where even the biggest and most luminous galaxies cannot be seen means that 25. A quasar is now thought to be. 26. Compared with stars in the disk, orbits of stars in the halo 27. galaxies are essentially featureless; their light shows the presence of only old red Main Sequence stars and red giant stars. 28. What observational fact convinces astronomers that the source of energy in a typical quasar is physically very small? 29. A radio galaxy, viewed from a position so that the observer is looking down one of the jets toward the galaxy, is a. 30. Where do we find supermassive black holes? 31. The central engine of an active galaxy appears to be. 32. Why are Cepheid variables important? 33. If double radio sources, quasars, and blazars are considered to be the same basic object, why do they appear to us to have very different and distinct properties? 34. Explain the main difference between quasars, blazars, and radio galaxies in the unified model of active galaxies. 35. Explain how gravitational lensing occurs. 36. What is the question asked in Olber's paradox of cosmology? 37. In stating his paradox, Olber expected the night sky to be bright and not dark as we see it because he thought that. 38. The resolution of Olber's paradox (i.e., the reason why the sky is dark at night) is that 39. Astronomers currently estimate the age of the universe to be. 40. What are two key observational facts that led to the widespread acceptance of the Big Bang model? 41. What is the cosmic microwave background radiation? 42. What significant event occurred about 380,000 years after the Big Bang started? 43. In cosmology, to what does the phrase critical density refer? Page 2

3 44. Recent results from very bright supernovae in very distant galaxies seem to indicate that the expansion of the universe is. 45. To an astronomer, what is a standard candle? 46. How do observations of distance galaxies help us learn about galaxy evolution? 47. What process slowed the collapse of protogalactic clouds? 48. Why were galaxy collisions believed to be more common in the past? 49. In the distance ladder, how do we determine distances to nearby stars? 50. Briefly explain why we think white-dwarf supernovae are useful for measuring cosmic distances. Page 3

4 Galaxies and Cosmology Review Game Answers 1. distance, particularly to stars in our galaxy and to nearby galaxies ,000 ly 3. diameter 100,000 light-years; disk thickness, 1000 light-years. 4. in the Milky Way halo 5. the disk and spiral arms 6. spiral 7. the rotation curve of our galaxy, which indicates higher than expected orbital speeds in the outer regions of the galaxy. 8. gravitational influence on visible stars. 9. a supermassive black hole 10. very rapid motion of matter close to the nucleus of the galaxy, requiring a very massive body to hold it in orbit 11. the very high orbital speed of stars close to the galactic center. 12. Hubble used observation of Cepheid variable stars and applied the period- luminosity relationship. 13. a barred spiral galaxy 14. a round, flat disk containing long lanes of stars that curve outward in a spiral shape from the edge of a round, nuclear region of uniform brightness 15. elliptical 16. primarily old, metal-poor stars 17. the redshift of light from distant galaxies, which increases with distance of the galaxy from Earth. 18. a cluster of about 40 galaxies of which the Milky Way is a member 19. Elliptical galaxies 20. Hubble s Law states that the velocity of a galaxy is proportional to its distance; more distance galaxies are moving away from us faster. 21. they are grouped in clusters, which are grouped into linked superclusters around huge voids (like soap bubbles). 22. The rotation curve of galaxies, showing orbital speeds of material, remains flat to large distances from the galactic center. 23. they are very distant, intrinsically luminous objects which give off more light than thousands of galaxies combined from a small region, and they are moving away from Earth at very high speeds. 24. they must be intrinsically far more luminous than the brightest galaxies. 25. the central core of an active galaxy. 26. are elliptical, with random orientation, like the orbits of comets in the Oort Cloud. 27. Elliptical 28. the rapid variation of the intensity of the source 29. blazar. 30. in the centers of both active and normal galaxies, both nearby and far away 31. a supermassive black hole at the center of an accretion disk, with jets of material being ejected perpendicular to the disk. 32. accretion disks around supermassive black holes. 33. Cepheids are pulsating variable stars and their pulsation periods are directly related to their true luminosities. Therefore we can use Cepheids as standard candles for distance measurements. 34. we see the accretion disk around the central black hole from a different angle in each Page 4

5 case face-on for blazars, edge-on for radio galaxies, and in between for quasars. 35. A massive object bends the light passing by from a more distant object behind it. 36. Why is the sky dark at night? 37. every line of sight should eventually intersect a star in an infinite universe randomly scattered with stars. 38. we cannot see those stars that are farther away from us than the distance that light has traveled since the beginning of the universe. 39. about 13.7 billion years old. 40. the background microwave radiation (CMB) and the high helium content of the universe; the CMB was emitted at the end of the era of nuclei as visible light (temp about 3,000K) and has been redshifted so that the peak of the radiation curve is in the millimeter wavelength which corresponds to a temperature of about 3K. The Big Bang theory predicts that the composition of the universe should be 75% hydrogen and 25% helium, by mass. No galaxy has a helium fraction lower than 25%. 41. radiation left over from the Big Bang, after the universe expanded and cooled 42. The universe became transparent to radiation. 43. the density of the universe above which the universe is bounded (closed) and below which it is unbounded (open) 44. accelerating (speeding up). 45. any type of object whose absolute magnitude is known 46. observations at different distances show galaxies of different ages and therefore different stages of evolution 47. the shock waves from the exploding supernovae of the earliest stars 48. galaxies were closer together when the universe was smaller (younger) 49. we find their distance using parallax which involves measuring the position of the star at six month intervals 50. They all come from explosions of WDs that reach the WD limit, so we expect them to have the same luminosity. Observations of nearby WD supernovae confirm this so we can use the apparent brightness of distant supernovae to calculate their distance from the luminositydistance formula. Page 5