Chapter 21
Basic Skills/Definitions Quiz
Part A
The unusually bright centers found in some galaxies are called ______.
Hint A.1
Study Section 21.3
ANSWER:

active galactic nuclei. halos. supermassive black holes. starbursts.
Part B
Telescopes being planned for the study of the earliest stages in galactic lives will be optimized for observations in ______.
Hint B.1
Study Section 21.1
ANSWER:

X rays. radio waves. infrared light. visible light.
Part C
What is an important starting assumption in most models for galaxy formation?
Hint C.1
Study Section 21.1
ANSWER:

Galaxies form first, then black holes. Black holes form first, seeding the formation of galaxies. All galaxies start out as spiral galaxies. Some regions in the universe start out denser than others.
Part D
Galaxies 2 billion years after the Big Bang tend to look like __________.
Hint D.1
Study Section 21.1
ANSWER:

Irregular galaxies. Spiral galaxies. Nothing - we can't see galaxies within 2 billion years of the Big Bang because they are outside the observable universe. Elliptical galaxies.
Part E
Collisions between galaxies typically unfold over a period of ______.
Hint E.1
Study Section 21.2
ANSWER:

thousands of years. several months. several days. hundreds of millions of years.
Part F
Why are collisions between galaxies more likely than collisions between stars within a galaxy?
Hint F.1
Study Section 21.2
ANSWER:

Galaxies travel through space much faster than stars. Relative to their sizes, galaxies are closer together than stars. Galaxies are much larger than stars. Galaxies have higher redshifts than stars.
Part G
Current understanding holds that a galaxy's type (spiral, elliptical, or irregular) ______.
Hint G.1
Study Section 21.2
ANSWER:

may either be the result of conditions in the protogalactic cloud that formed it or the result of later interactions with other galaxies. is determined by whether the galaxy is located in a cluster where collisions are likely or outside a cluster where collisions are less likely. may either be a result of the mass of the protogalactic cloud that formed it or the result of the heavy element abundance in that cloud. is always determined by the angular momentum of the protogalactic cloud that formed it.
Part H
Which of the following features is NOT a feature of a central dominant galaxy?
Hint H.1
Section 21.2
ANSWER:

They often have multiple galactic nuclei near their centers. They are often spiral galaxies. They are thought to form by the merger of several smaller galaxies. They're found in clusters of galaxies.
Part I
Why should galaxy collisions have been more common in the past than they are today?
Hint I.1
Study Sections 21.2.
ANSWER:

Galaxies attracted each other more strongly in the past because they were more massive; they had not yet turned most of their mass into stars and light. Galaxies were much bigger in the past since they had not contracted completely. Galaxies were more active in the past and therefore would have collided with each other more frequently. Galaxies were closer together in the past because the universe was smaller.
Part J
The distinguishing feature of a starburst galaxy is:
Hint J.1
Study Section 21.2
ANSWER:

a very large luminosity compared to the total luminosity of the Milky Way. a rate of star formation that may be 100 or more times greater than that in the Milky Way. Strong radio emission that apparently comes from "lobes" of material well outside the visible boundaries of the galaxy. the presence of an unusually large number of binary star systems that appear to X-ray telescopes as X-ray bursters.
Part K
According to current understanding, what is a quasar?
Hint K.1
Study Section 21.3
ANSWER:

A galaxy with an unusually high rate of star formation. An active galactic nucleus that is particularly bright. A very large galaxy thought to be formed by the merger of several smaller galaxies, typically found in the center of a galaxy cluster. Any object with an extremely large redshift is called a quasar.
Part L
Which of the following phenomena is probably NOT related to the presence of a supermassive black hole?
Hint L.1
Study Section 21.3
ANSWER:

The huge jets seen emerging from the centers of some galaxies. The radio emission from radio galaxies. Quasars The large sizes of central dominant galaxies.
Part M
The mass of the supermassive black hole thought to power a typical active galactic nucleus would be around ______.
Hint M.1
Study Section 21.3
ANSWER:

1 trillion solar masses. 10 solar masses 1 billion solar masses. 3 solar masses
Part N
According to the theory that active galactic nuclei are powered by supermassive black holes, the high luminosity of an active galactic nucleus primarily consists of ______.
Hint N.1
Study Section 21.3
ANSWER:

the combined light of thousands of young, high-mass stars that orbit the black hole. light emitted by hot gas in an accretion disk that swirls around the black hole. intense radiation emitted by the black hole itself. radio waves emitted from radio lobes found on either side of the galaxy we see in visible light.
Part O
According to the theory that active galactic nuclei are powered by supermassive black holes, the source of energy that supplies the power is _____.
Hint O.1
Study Section 21.3
ANSWER:

gravitational potential energy released by matter that is falling toward the black hole. matter-antimatter annihilation occurring just outside the event horizon of the black hole. nuclear fusion in the accretion disk surrounding the black hole. jets emerging from the accretion disk.
Part P
Intergalactic hydrogen clouds are easiest to study by looking at ______.
Hint P.1
Study Section 21.3
ANSWER:

x-ray emission. absorption lines in quasar spectra. radio emission from molecular hydrogen. 21 cm radio emission
Part Q
Hubble Space Telescope observations have shown that when the mass of the central black hole is very large, then ________.
Hint Q.1
Study Section 21.3
ANSWER:

The galaxy is always a spiral galaxy. The mass of the halo and disk of the host galaxy is also very large. The host galaxy is eventually completely consumed by the black hole. The mass of the bulge, or the spheroidal component, of the host galaxy is also very large.
Part R
The best evidence for the existence of supermassive black holes is:
Hint R.1
Study Section 21.3
ANSWER:

Huge dark regions in the centers of galaxies, where black holes have been consuming the galaxy from the inside out. Evidence for jet velocities that approach the speed of light. Large quantities of high-energy emission such as X-rays and gamma rays, and radio emission from relativistic electrons. Very high orbital velocities in a very compact region.