Astronomy- Ch. 27&28

isotropic

The same in all directions

merger (Galaxies)

a collision between galaxies (of roughly comparable size) that combine to form a single new structure

starburst

a galaxy or merger of multiple galaxies that turns gas into stars much faster than usual

supercluster

a large region of space (more than 100 million light-years across) where groups and clusters of galaxies are more concentrated; a cluster of clusters of galaxies

galactic cannibalism

a process by which a larger galaxy strips material from or completely swallows a smaller one

void

a region between clusters and superclusters of galaxies that appears relatively empty of galaxies

Local Group

a small cluster of galaxies to which our Galaxy belongs

15. The Hubble Space Telescope has enabled astronomers to explore an active galaxy such as M87 in remarkable detail. Which of the following observations of M87 is NOT an important part of the web of evidence that shows it must have a supermassive black hole at the center? a. the discovery of a gravitational lens in M87 b. the discovery that the distribution of stars in the galaxy becomes densely concentrated at the center (much more so than in normal elliptical galaxies) c. the discovery of an inner disk of rapidly swirling gas in the center of the galaxy d. the Doppler shifts measured for spectral lines coming from rapidly moving gas e. evidence that M87 may have grown to be a giant elliptical through collisions with other, smaller galaxies, some of whose material may have fallen into M87's center

a. the discovery of a gravitational lens in M87

19. How do astronomers explain the energetic jets that come out of quasars and active galactic nuclei in opposite directions? a. the jets are "spit out" from the chaotic accretion disks of supermassive black holes in directions that are perpendicular to the disk b. the jets are produced when a whole series of massive stars near the galaxy's center explode at the same time as supernovae c. the jets are connected with the dark matter in distant galaxies; this dark matter is in two large bubbles above and below the galaxy d. the jets are a kind of astronomical mirage, produced by gravitational lensing by a large mass between us and the quasar e. there is no current explanation for these jets; they are an unsolved mystery

a. the jets are "spit out" from the chaotic accretion disks of supermassive black holes in directions that are perpendicular to the disk

7. After several decades of observation, astronomers have concluded that quasars are a. very powerful and compact sources of energy at the centers of distant galaxies b. projectiles shot out of our own Galaxy and moving out into intergalactic space c. energetic collisions of comets in the Oort Cloud d. anti-matter stars in the halo of the Milky Way Galaxy e. a completely baffling mystery with no hint of an answer

a. very powerful and compact sources of energy at the centers of distant galaxies

dark energy

an energy that is causing the expansion of the universe to accelerate; the source of this energy is not yet understood

quasar

an object of very high redshift that looks like a star but is extragalactic and highly luminous; also called a quasi-stellar object or QSO

4. The astronomer who first solved the problem of the strange red-shifts seen in quasar spectra and thus helped us understand that the quasars must be distant objects was a. Carl Sagan b. Maarten Schmidt c. Edwin Hubble d. S. Chandrasekhar e. Vesto Slipher

b. Maarten Schmidt

10. An astronomer claims that the large redshifts of all quasars are caused by some new mechanism and not the expansion of the universe. The redshift tells us nothing, he says, about where any quasar is located. Which of the following would be a way to disprove his view of quasars? a. observe one quasar at all wavelengths of the electromagnetic spectrum b. find a number of cases where a quasar seen in a cluster of galaxies has the same redshift as all the galaxies in the cluster c. find a number of quasars that seem associated with a galaxy that has a different redshift from the quasar d. measure carefully how long the quasar takes to undergo regular changes in its light output e. demonstrate by observing many quasars that brighter-looking quasars have higher redshifts

b. find a number of cases where a quasar seen in a cluster of galaxies has the same redshift as all the galaxies in the cluster

12. What observation in astronomy, made AFTER the discovery of quasars, was a big help to astronomers in figuring out what quasars really were? a. the understanding that most stars become white dwarfs when they die and white dwarfs are much smaller than main-sequence stars b. the discovery that the Milky Way Galaxy has a black hole at the center with enough mass for 4 million Suns c. the discovery that the galaxies mostly show a red shift d. the discovery of exoplanets (planets orbiting other stars) throughout the Galaxy e. the discovery of Herbig-Haro objects around newly forming stars

b. the discovery that the Milky Way Galaxy has a black hole at the center with enough mass for 4 million Suns

14. Today, astronomers find compelling evidence that the energy source of the quasars and active galaxies is a. antimatter and matter colliding at the center of a galaxy b. chain reactions of supernova explosions c. matter falling toward a supermassive black hole at the center of a galaxy d. the left-over (and stored) energy of the big bang explosion e. you can't fool me; astronomers have no explanation for what the energy source is for the quasars -- they are completely baffled

c. matter falling toward a supermassive black hole at the center of a galaxy

17. How do astronomers now explain the fact that the energy emitting regions for quasars are so small? a. quasars are just optical illusions caused by gravitational lensing effects b. quasars are the result of three or four galaxies colliding: the collision squeezes the quasar to become much smaller than it normally would be c. quasars are the result of matter falling into a black hole; the event horizons of even supermassive black holes are extremely small on the cosmic scale d. quasars are caused by the actions of neutron stars and neutron stars have been squeezed so much that they are very, very small e. you can't fool me, there is no plausible explanation for the small sizes of quasar energy regions

c. quasars are the result of matter falling into a black hole; the event horizons of even supermassive black holes are extremely small on the cosmic scale

9. What makes astronomers believe that the energy source in quasars is only a few light months across (the distance light travels in a few months)? a. we have only seen the light from such quasars for a few months so far b. a few light months is about the size of a typical galaxy, and astronomers think quasars are active galaxies c. quasars show variations in their energy output that have a period of a few months d. 10 light months is about the size of the belt of comets around the solar system, and that is where we believe quasars are located e. the Hubble Law requires objects with high red shifts (like quasars) to be pretty close to us

c. quasars show variations in their energy output that have a period of a few months

5. Today we know that what all quasars have in common is that they appear to be small sources of energy with a. strong radio emission showing regular pulses b. no lines in the spectrum at all c. redshifts that indicate they are far away d. tremendous proper motion (apparent motion across the sky) e. gravitational lenses clearly visible around them

c. redshifts that indicate they are far away

13. Astronomers have established that quasars and active galaxies have a lot of mass at their centers in a very small volume of space. Why can't this mass be in the form of a cluster of stars that are quite close to each other? a. all the clusters of stars are at the outer edges of galaxies; we have never seen any clusters of stars toward the middle of galaxies b. things at the centers of galaxies all move so fast, the stars in the cluster would be launched outward and would never remain at the center c. to fit as much matter into the cluster as we observe, the stars in the cluster must be so close to each other they would merge into a superstar and soon collapse into a black hole d. we could easily observe such a star cluster in distant galaxies, and we don't see them e. none of the above

c. to fit as much matter into the cluster as we observe, the stars in the cluster must be so close to each other they would merge into a superstar and soon collapse into a black hole

3. A distant quasar shows a large redshift -- one so large, in fact, that the features we now see in the visible-light region of the spectrum would be invisible to us, were it not for the redshift. What band of the electro-magnetic spectrum were these features most likely in, before the spectrum was redshifted? a. radio b. infrared c. ultraviolet d. microwaves e. gamma-ray

c. ultraviolet

evolution (of galaxies)

changes in individual galaxies over cosmic time, inferred by observing snapshots of many different galaxies at different times in their lives

1. A Congressman from Texas visits our National Observatory in Tucson, Arizona, and wants to be shown an object in the universe with the "biggest darn redshift you ever saw". What type of object should the astronomers show him? a. a comet in the Kuiper Belt b. one of the galaxies in our Local Group of galaxies c. a star with a very low surface temperature d. a quasar e. an active galaxy that is in a rich cluster of galaxies just beyond the Local Group

d. a quasar

6. What method would astronomers use to find the distance to a remote quasar? a. parallax b. Cepheid variables c. measuring the size of its dark matter halo d. finding the redshift and using Hubble's Law e. the turnoff point of the main sequence on an H-R diagram

d. finding the redshift and using Hubble's Law

18. When quasars "shine" (in visible light and other kinds of radiation) with a lot of energy, where (what location) does this huge amount of energy come from? a. from the outer spiral arms of the galaxy in which the quasar is located b. from inside the event horizon of a supermassive black hole c. from supernova explosions (a whole bunch of them all at once) in the galaxy in which the quasar is located d. from an accretion disk around a supermassive black hole e. from a much more distant object that happens to lie behind the quasar and fools us into thinking the quasar is shining

d. from an accretion disk around a supermassive black hole

11. Which of the following observations is a convincing argument for the idea that quasars are located inside galaxies? a. quasars have been discovered in more than one direction in space b. quasars appear to be small in angular extent (they look like points) c. quasars vary in brightness with time d. relatively nearby quasars show "fuzz" around them with the same spectra and redshift as the quasar e. you can't fool me; there is no evidence whatsoever that quasars are connected with galaxies

d. relatively nearby quasars show "fuzz" around them with the same spectra and redshift as the quasar

16. A friend of yours who is a science fiction fan hears you talk about the fact that astronomers now believe that the mechanism for the large energy output of quasars involves a supermassive black hole. He challenges you, saying something like "Oh come on, every science fiction fan knows that nothing, not even light, can escape from a black hole! How can a black hole be an energy source?" How would you respond to his objection? a. you're right, my explanation doesn't make sense; I wonder why astronomers didn't think of that? b. light can't escape from the event horizon of a regular black hole; but it can easily escape from the event horizon of a supermassive black hole c. it isn't light that escapes from the black holes in quasars, but x-rays and gamma-rays, which work by completely different rules d. the energy we see from quasars comes from regions where matter is falling in; these regions are still outside the event horizon e. quasars act like gravitational lenses and bend spacetime until light and other radiation CAN emerge from a black hole in unexpected ways

d. the energy we see from quasars comes from regions where matter is falling in; these regions are still outside the event horizon

8. If quasars are at the distances most astronomers believe they are, then (for the most luminous ones) their luminosities must be: a. like the Sun b. like the combined luminosity of a cluster of a hundred stars c. much fainter than the Sun d. like the accretion disk of a black hole formed from a single star (like Cygnus X-1) e. like the combined luminosity of a hundred trillion (1014) Suns

e. like the combined luminosity of a hundred trillion (10^14) Suns

2. If quasars often resemble little blue stars, what was it about them that so surprised astronomers when they were discovered? a. their surface temperatures were among the lowest measured b. they show absolutely no lines in the spectrum c. they all showed a blue-shift in their spectra d. they were all located in globular clusters e. their spectral lines were at first hard to recognize and then turned out to have large redshifts

e. their spectral lines were at first hard to recognize and then turned out to have large redshifts

active galactic nuclei (AGN)

galaxies that are almost as luminous as quasars and share many of their properties, although to a less spectacular degree; abnormal amounts of energy are produced in their centers

active galaxies

galaxies that house active galactic nuclei

homogeneous

having a consistent and even distribution of matter that is the same everywhere

Hot dark Matter

massive particles, not yet identified, that don't absorb, emit, or reflect light or other electromagnetic radiation; hot dark matter is faster-moving material than cold dark matter

cold dark matter

slow-moving massive particles, not yet identified, that don't absorb, emit, or reflect light or other electromagnetic radiation

cosmological principle

the assumption that, on the large scale, the universe at any given time is the same everywhere—isotropic and homogeneous