27.3.0 Quasars as Probes of Evolution in the Universe

22. Why do astronomers think that there are fewer quasars today than there were billions of years ago? a. quasars are seen when the supermassive black hole at the center of a galaxy has a lot of "food to eat" (stars and gas) and the amount of available food tends to decrease with time b. quasars are supermassive black holes at the centers of galaxies, and such black holes are constantly losing mass and thus getting less and less able to pull on anything c. quasars tend to merge all the time, and so there are fewer and fewer of them as time goes on d. quasars are caused by many supernovae going off at the same time, and massive stars only exploded in the early history of the universe; they don't explode today e. no one has the slightest idea on how to answer this question; it is completely unsolved

a. quasars are seen when the supermassive black hole at the center of a galaxy has a lot of "food to eat" (stars and gas) and the amount of available food tends to decrease with time

26. For galaxies that have super-massive black holes at their centers, how do astronomers find that the mass of the host galaxy and the mass of the black hole are related? a. the more massive the galaxy, the more massive the central black hole b. the more massive the galaxy, the less massive the central black hole c. all super-massive black holes have roughly the same amount of mass d. once the mass of a galaxy reaches a certain size, it is not possible to form a black hole in the center at all; only galaxies smaller than this limit can have central black holes e. none of the above

a. the more massive the galaxy, the more massive the central black hole

25. How can supermassive black holes at the centers of galaxies help new stars to form in that galaxy? a. new stars can form in the accretion disk just before they are pulled into the black hole b. new stars can form when the flow of particles from a black hole accretion disk or jet compresses the material some distance away from the black hole and starts the "clumping" that leads to the formation of stars c. such supermassive black holes often explode and their huge explosion can force the forming of new stars d. after billions of years, when black holes no longer have an active accretion disk, they can turn into a cluster of new stars e. so much material comes out of the event horizon of supermassive black holes, there is more than enough new material for generations of stars

b. new stars can form when the flow of particles from a black hole accretion disk or jet compresses the material some distance away from the black hole and starts the "clumping" that leads to the formation of stars

27. An astronomer who loved reading the Guinness Book of World Records when she was a child becomes obsessed with quasars and wants desperately to find the most distant quasar ever (the one with the largest redshift.) Where should she be looking to have the best chance of finding such a quasar? a. in the centers of nearby galaxies b. in the constellation of Sagittarius, the direction where we see the center of the Milky Way c. right next to 3C273, the first quasar that was understood d. in or near a distant cluster of galaxies that can act like a gravitational lens e. there is simply no way that she can improve her chances of finding such a quasar; such discoveries are completely random

d. in or near a distant cluster of galaxies that can act like a gravitational lens

24. How are galaxies and quasars related? a. quasars can be seen in front of galaxies, but they have nothing to do with them b. quasars can only be seen behind galaxies, but they have nothing to do with them c. quasars and galaxies are never seen together and they have nothing to do with each other d. quasars are active supermassive black holes at the centers of galaxies e. quasars are a complete mystery; so it is not possible to say how they might be related to galaxies

d. quasars are active supermassive black holes at the centers of galaxies

23. If a nearby galaxy still acts like a quasar today, what is the most likely explanation? a. the galaxy was formed recently, and is just now going through its "adolescence" b. the galaxy must have an enormous Doppler shift and must have traveled here from a large distance away c. the galaxy must be made entirely of very massive stars; very few low mass stars exist in it d. the galaxy must be undergoing a collision with another galaxy that is providing fresh fuel for its central black hole e. the dark matter in the galaxy must be undergoing a transformation into matter we can see

d. the galaxy must be undergoing a collision with another galaxy that is providing fresh fuel for its central black hole

21. How do quasars demonstrate that the universe evolves with time? a. there were very few quasars long ago, and their numbers have been growing since b. quasars began emerging only about a billion years ago, and now there are many more than ever c. quasars have been around since the big bang, but the radiation they give off gets stronger and stronger as time in the universe goes on d. the number of quasars reached a maximum some time ago, and now the numbers have been declining e. quasars actually don't demonstrate any evolution; the number of quasars has been pretty constant for the entire history of the universe

d. the number of quasars reached a maximum some time ago, and now the numbers have been declining

20. When astronomers make counts of how many quasars there are at different distances from us, what do they find? a. there are more quasars closer to us than farther away b. the largest number of quasars can be found at about a distance of 1 million LY away from us c. the number of quasars is pretty much the same at every range of distances (as many are close to us as far away) d. the largest number of quasars were found exactly at the time of the big bang (when the universe began); quasars have been declining steadily in numbers ever since e. the largest number of quasars can be seen at about the distance corresponding to a time when the universe was only 20% its current age (a time when the universe was still young)

e. the largest number of quasars can be seen at about the distance corresponding to a time when the universe was only 20% its current age (a time when the universe was still young)