Chapter 21: Galaxy Evolution

Flashcard maker : August Dunbar
How do observations of distant galaxies help us learn about galaxy evolution?
observations at different distances show galaxies of different ages and therefore different stages of evolution
Why are telescopes sometimes called “time machines”?
because observations of distant objects reveal them as they were in the past
I observe a galaxy that is 100 million light-years away: what do I see?
the light from the galaxy as it was 100 million years ago and it is redshifted
Which of the following gives the two main assumptions of theoretical models of galaxy evolution?
hydrogen and helium filled all of space and certain regions of the universe were slightly denser than others
Which of the following processes slowed the collapse of protogalactic clouds?
the shock waves from the exploding supernova of the earliest stars
Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy?
a dense cloud with very little angular momentum
Why is a dense cloud more likely to produce an elliptical galaxy than a spiral galaxy?
the higher gas density forms stars more efficiently so all the gas is converted into stars before a disk can form
What evidence supports the theory that elliptical galaxies come from denser clouds?
elliptical galaxies at high redshifts lack young blue stars
If we represent the Milky Way Galaxy as the size of a grapefruit (10-cm diameter), the distance to the Andromeda Galaxy would be about
3 m
Why should galaxy collisions have been more common in the past than they are today?
galaxies were closer together in the past because the universe was smaller
What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?
all of the above
Which of the following is not a strong argument for the theory that some large elliptical galaxies formed as the result of galaxy collisions?
galaxy collisions are common and most galaxies in the universe are elliptical
What is a central dominant galaxy?
a giant elliptical galaxy at the center of a dense cluster
How many more stars does a starburst galaxy form, in one year, than the Milky Way?
about a hundred
Why do we believe that starburst galaxies represent a temporary stage in galaxy evolution?
such galaxies produce so much light that they would have consumed all their gas long ago if they had always been forming stars at this high rate
Starburst galaxies produce most of their light in the wavelength range of
the infrared
What evidence suggests that small galaxies in our Local Group have undergone two or more starbursts in the past?
we see small galaxies in which many stars have one age and many others have another age that is billions of years older
In the 1960s, Maarten Schmidt determined that quasars were very distant objects by
determining their redshift
What is a quasar?
the extremely bright center of a distant galaxy thought to be powered by a massive black hole
Which of the following is not true of quasars?
they are powered by the intent production of large numbers of stars that can only be sustained for a relatively short time
Which of the following is evidence for supermassive black holes in active galaxies?
all of the above
The most active galactic nuclei are usually found at large distances from us; relatively few nearby galaxies have active galactic nuclei. What does this imply?
active galactic nuclei tend to become less active as they age
What is a galactic wind?
hot gas erupting into intergalactic space from a large superbubble
If an object doubles its luminosity in 10 hours, how large can the emitting source of light be?
about 10 light hours across
Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude?
the x ray source is no more than a few light days in diameter
Which of the following is not a piece of evidence supporting the conclusion that active galactic nuclei are powered by accretion disks around massive black holes?
infrared observations show that many stars forming near the centers of active galaxies
How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced?
by gravity which converts potential energy of matter falling towards a central black hole into kinetic energy which is then converted to thermal energy by collisions among the particles of matter
Where are the X rays produced that are emitted by quasars and other active galactic nuclei?
in hot gas in an accretion disk around a central black hole
How do we know that there are intergalactic clouds between a distant quasar and us?
we see hydrogen absorption lines at redshifts smaller than that of a quasar
What are the typical features seen in quasar absorption lines of intergalactic clouds?
the hydrogen line is wider and lines from heavy elements are weaker at higher redshifts
Which of the following cannot be true of the very first stars formed in the Universe?
they may have had rocky planets around them
All of the following are true. Which of these gives evidence that quasars were more common in the early stages of the universe?
they are more common at very great distances
2) Which of the following is an important starting assumption in models of galaxy formation?
A) Galaxies form first, then black holes.
B) All galaxies start out as spiral galaxies.
C) Black holes form first, seeding the formation of galaxies.
D) Some regions in the universe start out denser than others.
5) Why are collisions between galaxies more likely than collisions between stars within a galaxy?
A) Relative to their sizes, galaxies are closer together than stars.
B) Galaxies are much larger than stars.
C) Galaxies travel through space much faster than stars.
D) Galaxies have higher redshifts than stars.
9) The unusually bright centers found in some galaxies are called
A) active galactic nuclei.
B) halos.
C) supermassive black holes.
D) starbursts.
10) According to current understanding, what is a quasar?
A) an active galactic nucleus that is particularly bright
B) a very large galaxy thought to be formed by the merger of several smaller galaxies, typically found in the center of a galaxy cluster
C) any object with an extremely large redshift is called a quasar
D) a galaxy with an unusually high rate of star formation
12) The mass of a supermassive black hole thought to power a typical bright active galactic nucleus is roughly
A) 3 solar masses.
B) 10 solar masses.
C) 1 trillion solar masses.
D) 1 billion solar masses.
13) 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
A) light emitted by hot gas in an accretion disk that swirls around the black hole.
B) intense radiation emitted by the black hole itself.
C) the combined light of thousands of young, high-mass stars that orbit the black hole.
D) radio waves emitted from radio lobes found on either side of the galaxy we see in visible light.
14) According to the theory that active galactic nuclei are powered by supermassive black holes, the energy released as light comes from
A) nuclear fusion in the accretion disk surrounding the black hole.
B) gravitational potential energy released by matter that is falling toward the black hole.
C) matter-antimatter annihilation occurring just outside the event horizon of the black hole.
D) jets emerging from the accretion disk.
16) Hubble Space Telescope observations have shown that when the mass of the central black hole is very large, then
A) the mass of the halo and disk of the host galaxy is also very large.
B) the host galaxy is eventually completely consumed by the black hole.
C) the galaxy is always a spiral galaxy.
D) the mass of the bulge of the host galaxy is also very large.
17) The best evidence for the existence of supermassive black holes is
A) very high orbital velocities in a very compact region.
B) evidence for jet velocities that approach the speed of light.
C) large quantities of high-energy emission such as X-rays and gamma rays, and radio emission from relativistic electrons.
D) huge dark regions in the centers of galaxies, where black holes have been sucking in the galaxy from the inside out.
10) A quasar’s spectrum is hugely redshifted. What do most astronomers think this large redshift tells us about the quasar?
A) the composition of the quasar
B) the distance to the quasar
C) the size of the quasar’s central, supermassive black hole
D) the type of host galaxy in which the quasar resides
12) Most active galactic nuclei are found at large distances from us, with relatively few nearby. What does this imply?
A) Supermassive black holes existed only when the universe was young, and no longer exist today.
B) Active galactic nuclei can form only at large distances from the Milky Way.
C) Active galactic nuclei exist tend to become less active as they age.
D) The jets seen in many active galactic nuclei must cause them to move far away from us.
16) The observed relationship between the masses of central black holes and the bulge masses of galaxies implies that
A) the black hole will eventually suck in the rest of the galaxy.
B) galaxy formation and supermassive black hole formation must be related somehow.
C) the biggest galaxies have the most luminous quasars.
D) quasars were more common 10 billion years ago than they are today.
17) Quasar spectra often show many absorption lines that all appear to be due to the same electron transition (such as level 1 to level 2 in hydrogen) but that fall at different wavelengths in the spectrum. Why do we think this is the case?
A) We are seeing absorption lines from clouds of gas that lie between us and the quasar, and therefore each cloud has a different redshift.
B) Quasars are rotating rapidly, and this rotation produces spectral lines with a wide variety of Doppler shifts.
C) The lines fall at different wavelengths because they are produced by different chemical elements.
D) No one knows—it remains perhaps the greatest mystery about quasars.

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