TEST BANK 21ST CENTURY ASTRONOMY THE SOLAR SYSTEM 5TH EDITION BY KAY
IF You Want To Purchase A+ Work Then Click The Link
Below , Instant Download
|
Chapter 19: Galaxies
Learning
Objectives.
Define the bold-faced vocabulary terms within the chapter.
19.1 Galaxies Come in Different Shapes and
Sizes
Evaluate how well Shapley and Curtis’s arguments about, and
Hubble’s measurements of, the nature of galaxies conform to the established
process of science laid out in this text.
Multiple Choice: 1, 2, 4, 11, 14, 16
Short Answer: 5, 6
Illustrate the essential morphological (shape)
characteristics of the Hubble types of galaxies.
Multiple Choice: 3, 5, 6, 7, 8, 28
Short Answer: 3, 4
Show how stellar orbits determine the morphology of a galaxy
or its components.
Multiple Choice: 15
Short Answer: 1
Compare and contrast spiral and elliptical galaxies in terms
of their gas and dust content, color, luminosity, stellar populations, and mass.
Multiple Choice: 9, 10, 12, 13, 17, 18
Short Answer: 2
19.2 Astronomers Use Several Methods to
Find Distances to Galaxies
Illustrate why measurements to increasingly distant objects
require overlapping scales, each building on the previous “rung” of a “distance
ladder.”
Multiple Choice: 26
Short Answer: 8
Explain what is meant by “standard candle.”
Multiple Choice: 19, 22, 23
Compare and contrast the observations needed to use the
various distance indicators in this chapter, including Cepheids, Type Ia
supernovae, and Hubble’s law.
Multiple Choice: 20, 21, 24, 25, 27, 29
Short Answer: 9, 10, 11
19.3 Galaxies Are Mostly Dark Matter
Explain how the amount of matter inferred from
electromagnetic radiation can differ from that inferred from gravity.
Multiple Choice: 43
Short Answer: 17, 18
Illustrate how flat rotation curves imply the need for dark
matter.
Multiple Choice: 42, 52
Short Answer: 16, 19
Summarize the observational evidence for dark matter in
spiral and elliptical galaxies.
Multiple Choice: 44, 48, 49, 50, 51, 53
Short Answer: 15
Compare and contrast the behavior of normal and dark matter.
Multiple Choice: 45
Summarize the candidates for dark matter, and the
observational evidence supporting or refuting each candidate.
Multiple Choice: 46, 47
Short Answer: 14
19.4 Most Galaxies Have a Supermassive
Black Hole at the Center
Explain why astronomers initially believed quasars were
stars.
Multiple Choice: 59, 61, 68
Illustrate how the period of variability of an object places
limits on its physical size.
Multiple Choice: 63, 67, 69
Short Answer: 26, 30
Summarize the observational evidence for galaxies containing
supermassive black holes at their centers, since black holes emit no observable
radiation of their own.
Multiple Choice: 70
Explain how an AGN differs from the nucleus of an ordinary
galaxy.
Multiple Choice: 57, 60, 62, 64, 66
Short Answer: 22, 23, 25, 28, 29
Illustrate the unified model of AGN and how different
perspectives can lead to classification of the central engine as a different
type of AGN.
Multiple Choice: 58, 65
Short Answer: 21, 24, 27
Working It Out 19.1
Use the relationship between distance, luminosity, and
brightness to calculate the distance to a standard candle.
Short Answer: 7
Working It Out 19.2
Use Doppler shifts and the Hubble redshift-distance law to
relate recessional velocity, redshift, and distance.
Multiple Choice: 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
41
Short Answer: 12, 13
Working It Out 19.3
Calculate the size, density, and accretion rate of a
supermassive black hole.
Short Answer: 20
MULTIPLE CHOICE
1.
What caused early
astronomers to believe that our galaxy is only about 6,000 light-years across?
a.
Telescopes were not
powerful enough to observe stars farther away.
b.
Interstellar dust
blocked visible light from stars farther away.
c.
Stars farther away
could not be resolved as individual objects.
d.
Astronomers
miscalculated the distances to stars, believing that the stars were 50 times
closer than they actually were.
e.
Astronomers assumed all
red stars were faint main- sequence stars, and they confused more luminous red
giants with them.
2.
In the Great Debate of
1920, Curtis and Shapley argued over whether or not
a.
the Big Bang occurred.
b.
the age of the universe
was 14 billion years.
c.
the universe was contracting.
d.
life existed outside
Earth.
e.
the spiral nebulae were
located outside the Milky Way.
3.
Which of the following
Hubble images shows an edge-on disk galaxy?
4.
Astronomers have known
that galaxies are separate entities outside of our own for roughly the last
a.
35 years.
b.
60 years.
c.
90 years.
d.
150 years.
e.
210 years.
5.
The Hubble
classification scheme for galaxies sorts them by their
a.
evolutionary state.
b.
mass.
c.
amount of dust.
d.
amount of dark matter.
e.
visual appearance.
6.
What type of galaxy is
shown in the figure below?
a.
a giant elliptical
b.
an ordinary spiral
galaxy
c.
an irregular galaxy
d.
a barred spiral
e.
a dwarf elliptical
7.
What type of galaxy is
shown in the figure below?
a.
a giant elliptical
b.
a regular spiral galaxy
c.
an irregular galaxy
d.
a barred spiral
e.
a dwarf elliptical
8.
In spiral galaxies, the
size of the central bulge is correlated with the
a.
tightness of the spiral
arms.
b.
luminosity of the
galaxy.
c.
age of the galaxy.
d.
thickness of the disk.
e.
presence of an active
nucleus.
9.
Active star formation
does not typically occur in elliptical galaxies because they
a.
rotate too fast.
b.
contain little
molecular hydrogen.
c.
are too massive.
d.
are too far away.
e.
usually contain active
nuclei.
10.
Elliptical galaxies
appear red because they
a.
are moving away from
us.
b.
contain mostly ionized
hydrogen gas.
c.
contain mostly old
stars.
d.
contain lots of dust.
e.
contain a mix of old
and young stars.
11.
One of the first
philosophical speculations about the nature of spiral nebulae being “island
universes” like our Milky Way, only much farther, came from
a.
Charles Messier.
b.
Immanuel Kant.
c.
Edwin Hubble.
d.
Harlow Shapley.
e.
Heber Curtis.
12.
The dark features in
the HST image in in the figure shown below indicate
a.
collections of cool
stars.
b.
clumps of dark matter.
c.
copious amounts of dark
energy.
d.
large amounts of dust.
e.
faulty pixels on the
CCD camera.
13.
The receding speed of
spiral galaxies may also render their colors __________ due to
__________________.
a.
bluer; relativistic
beaming
b.
bluer; Doppler effect
c.
redder; relativistic
beaming
d.
redder; Doppler effect
e.
redder; galactic
interactions
14.
What did Edwin Hubble
study in the Andromeda Galaxy that proved it was an individual galaxy and not
part of our own Milky Way?
a.
Cepheid stars
b.
Type Ia supernovae
c.
globular clusters
d.
red giant stars
e.
RR Lyrae variables
15.
Stars in the disks of
spiral galaxies have orbits that are
a.
randomly oriented.
b.
constantly getting
larger.
c.
mostly aligned in the
same plane.
d.
spiral-shaped.
e.
unaffected by dark
matter.
16.
The nearest big galaxy,
Andromeda, is at an estimated distance of
a.
780 Mpc.
b.
0.78 kpc.
c.
0.78 Mpc.
d.
2.5 × 106 kpc.
e.
250 × 103 Mpc.
17.
The disks of spiral
galaxies appear blue because
a.
they are moving toward
us.
b.
they contain a
relatively high concentration of low-mass stars.
c.
they contain active
regions of star formation.
d.
they contain more
metals that, when ionized, emit blue light.
e.
stars collide with each
other frequently in these dense regions and explode as Type Ia supernovae.
18.
Which of the following
would not be found in an elliptical
galaxy?
a.
low-mass stars
b.
Type Ia supernovae
c.
Type II supernovae
d.
planetary nebulae
e.
hot gas
19.
To be a standard candle,
an object must have a constant
a.
lifetime.
b.
brightness.
c.
luminosity.
d.
distance.
e.
mass.
20.
According to Hubble’s
law, as the distance of a galaxy ____________ its _______________ increases.
a.
increases; luminosity
b.
increases; recessional
velocity
c.
decreases; luminosity
d.
decreases; recessional
velocity
e.
decreases; peculiar
velocity
21.
Astronomers use
galactic redshift to estimate
a.
gravity.
b.
luminosity.
c.
velocity.
d.
mass.
e.
distance.
22.
Why can Type Ia
supernovae be used to determine a galaxy’s distance?
a.
Type Ia supernovae
occur only in very luminous galaxies.
b.
Most Type Ia supernovae
have approximately the same luminosity.
c.
Most Type Ia supernovae
have approximately the same size.
d.
A Type Ia supernova
occurs in a typical galaxy about once every 100 years.
e.
Type Ia supernovae
occur even in very small galaxies.
23.
Which distance
indicator can be used to measure the most distant objects?
a.
Cepheids
b.
Parallax
c.
Type Ia supernovae
d.
main-sequence fitting
e.
RR Lyrae stars
24.
If the distance of a
galaxy at a redshift z = 0.5 is 1,800 Mpc, how many years back into the past are we
looking when we observe this galaxy?
a.
500 million years
b.
2 billion years
c.
6 billion years
d.
9 billion years
e.
10 billion years
25.
The spectra of most
galaxies tell us that
a.
galaxies appear to be
moving away from us.
b.
their light comes
predominantly from objects other than stars.
c.
most galaxies contain
clouds of gas that are absorbing their favorite wavelengths.
d.
galaxies in the past
rotated at a faster rate than they do today.
e.
galaxies are rushing
through space in all directions.
26.
Which of the following
lists distance indicators from nearest to farthest?
a.
Cepheids, parallax,
main-sequence fitting, Type Ia supernovae
b.
parallax, main-sequence
fitting, Cepheids, Type Ia supernovae
c.
parallax, main-sequence
fitting, Type Ia supernovae, Cepheids
d.
main-sequence fitting,
parallax, Cepheids, Type Ia supernovae
e.
Cepheids, Type Ia
supernovae, main-sequence fitting, parallax
27.
The Tully-Fisher method
of determination of distances to galaxies is based on the correlation between
a.
color and redshift.
b.
star formation rate and
morphological type.
c.
width of emission lines
and black hole accretion rate.
d.
rotational speed and
luminosity.
e.
dark matter radial
profile and X-ray brightness.
28.
Which galaxies are
sometimes called “armless” disks?
a.
ellipticals
b.
irregulars
c.
dwarfs
d.
SOs
e.
barred spirals
29.
Type Ia supernovae have
an absolute magnitude of −19.3. If you discover a Type Ia supernovae in a distant
galaxy that has an apparent magnitude of 22, then how far away is this galaxy?
a.
0.3 Mpc
b.
40 Mpc
c.
1,200 Mpc
d.
1,800 Mpc
e.
3,500 Mpc
30.
The nearest known
quasar shows a redshift of z = 0.0516, which
means it is at a distance of
a.
220 Mpc.
b.
450 Mpc.
c.
100 Mpc.
d.
15400 Mpc.
e.
100 kpc.
31.
For the more distant
quasars, the emission lines that would normally occur in the visible domain
would be shifted into
a.
UV.
b.
X-rays.
c.
gamma rays.
d.
IR.
e.
radio.
32.
A certain spectral line
of rest wavelength lrest (i.e., laboratory value) is shifted by 100 nm in a quasar. A
second line with a rest wavelength half the (rest) value of the first one would
be shifted by
a.
200 nm.
b.
100 nm.
c.
500 nm.
d.
50 nm.
e.
1000 nm.
33.
If a galaxy has an
apparent velocity of 700 km/s, what is its distance if the Hubble constant is
assumed to be 70 km/s/Mpc?
a.
10 Mpc
b.
70 Mpc
c.
100 Mpc
d.
700 Mpc
e.
1,000 Mpc
34.
If you found a galaxy
with an Hα emission line that had a wavelength of 756.3 nm, what would
be the galaxy’s redshift? (Note that the rest wavelength of the Hα emission line is
656.3 nm.)
a.
0.05
b.
0.07
c.
0.10
d.
0.13
e.
0.15
35.
If the distance of a
galaxy is 10 Mpc, what is its recessional velocity if the Hubble constant is
assumed to be 70 km/s/Mpc?
a.
700 km/s
b.
1,000 km/s
c.
3,500 km/s
d.
5,000 km/s
e.
7,000 km/s
36.
You see a galaxy in
which the Hα line (rest wavelength = 656.3 nm) is
observed at a wavelength of 756.3 nm. What would be the observed wavelength of
a particular helium line that has a rest wavelength of 1,083 nm?
a.
1,083 nm
b.
1,183 nm
c.
1,248 nm
d.
1,440 nm
e.
3,142 nm
37.
If a galaxy has a
recessional velocity of 50,000 km/s, at what wavelength will you observe the Hαemission line?
(Note that the rest wavelength of the Hα emission line is
656.3 nm.)
a.
695.7 nm
b.
719.4 nm
c.
742.3 nm
d.
765.7 nm
e.
1750 nm
38.
If you found a galaxy
with an Hα emission line that had a wavelength of 756.3 nm, what would
be the galaxy’s distance if the Hubble constant is 70 km/s/Mpc? (Note that the
rest wavelength of the Hα emission line is 656.3 nm.)
a.
650 Mpc
b.
760 Mpc
c.
3,200 Mpc
d.
6,400 Mpc
e.
7,600 Mpc
39.
If the spectrum of a
distant galaxy is observed to have a calcium K absorption line that occurs at a
wavelength of 500.4 nm, what is this galaxy’s distance if the rest wavelength
of this absorption line is 393.4 nm? Assume the Hubble constant is 70 km/s/Mpc.
a.
720 Mpc
b.
952 Mpc
c.
1,166 Mpc
d.
2,580 Mpc
e.
3,730 Mpc
40.
In the figure shown
below, the upper spectrum is from hydrogen at rest in a laboratory, and the
lower spectrum is from a galaxy. How far away is this galaxy?
a.
110 Mpc
b.
170 Mpc
c.
230 Mpc
d.
280 Mpc
e.
340 Mpc
41.
You read about the
discovery of quasars with redshift z larger than 1. This means that
a.
their host galaxies are
receding at speeds exceeding the speed of light.
b.
the measurements of
redshift must be wrong, z cannot exceed 1.
c.
the relationship
between z and receding speed must account for relativistic corrections.
d.
the speed of light can
exceed c in the case of distant quasars.
e.
quasars must contain a
lot of dark matter.
42.
The rotation curve of a
galaxy is a plot of the rotation speed as a function of the
a.
galaxy’s luminosity.
b.
mass of the dark matter
halo.
c.
brightness of the
luminous matter in the galaxy.
d.
radius from the center.
e.
ages of star clusters.
43.
If you measure the
velocity of a cloud of gas that is rotating around the center of a galaxy in a
circular orbit with radius R, you can determine the
a.
total mass of the
galaxy.
b.
mass of the stars and
gas in the galaxy.
c.
mass of the galaxy
enclosed within the radius R.
d.
mass of the galaxy
located outside the radius R.
e.
mass of luminous matter
within the radius R.
44.
What makes up the
majority of the mass of an individual spiral galaxy?
a.
a central supermassive
black hole
b.
dark matter
c.
massive O- and B-type
stars
d.
cold molecular gas
clouds
e.
low-mass G-, K-, and
M-type stars
45.
Dust in galaxies does
not count as dark matter because
a.
it absorbs only some
wavelengths of light but not all wavelengths as dark matter does.
b.
it interacts with
light.
c.
it is found only in
spiral disks, whereas dark matter is also found in elliptical galaxies, too.
d.
dust is easily
destroyed by dark matter.
e.
there is never enough
to account for all the gravity in galaxies.
46.
Dark matter is most
likely made up of
a.
elementary particles
that have mass but do not interact much with normal matter.
b.
supermassive black
holes.
c.
faint stellar remnants
such as white dwarfs and neutron stars.
d.
free-floating Jupiter-mass
planets.
e.
cold concentrations of
dust.
47.
How have astronomers
searched for evidence of MACHOs in the halo of the Milky Way?
a.
They search for stars
that are binary companions of MACHOs.
b.
They search for rapidly
moving, massive gas clouds.
c.
They search for disturbances
in the background of gravitational waves.
d.
They search for distant
stars with light briefly amplified by gravitational lensing.
e.
They search for close
binary stars undergoing mass transfer.
48.
The density of ordinary
luminous matter can exceed the density of dark matter in which parts of
galaxies?
a.
everywhere inside
galaxies
b.
only in the outer
regions of galaxies
c.
only in star clusters
d.
near the centers of
galaxies
e.
only around an AGN
49.
Roughly what percentage
of the total mass of a galaxy is made up of luminous, or normal, matter?
a.
5–10 percent
b.
25–30 percent
c.
40–50 percent
d.
70–75 percent
e.
90–95 percent
50.
How did astronomers
determine that elliptical galaxies are composed mostly of dark matter?
a.
They measured the
velocities of stars in the inner regions of the galaxies.
b.
They measured the
rotation rates of gas as a function of distance from the centers of the
galaxies.
c.
They measured the
amount of gravitational pull elliptical galaxies have on companion galaxies.
d.
They assumed that the
proportion of dark matter was roughly the same as in spiral galaxies.
e.
They measured the X-ray
emission from hot gas gravitationally bound to the galaxies.
51.
How can we measure the
mass of an elliptical galaxy?
a.
by measuring the speeds
of stars in the nucleus
b.
by observing the
velocity of the hot, X-ray emitting gas that surrounds the galaxy
c.
by measuring the number
of H II regions in the galaxy
d.
by measuring how many
supernovae go off each century
e.
by measuring the amount
of blue light in the galaxy
52.
For which galaxies
would it be easiest to measure rotation curves?
a.
elliptical
b.
face-on barred spirals
c.
face-on normal spirals
d.
face-on S0s
e.
edge-on spirals
53.
If a galaxy had no dark
matter, how would the velocity (v) of a star that orbited far outside
the visible extent of the galaxy depend on its distance (r) from the
center of the galaxy? Hint: Think about the Keplerian motion of planets around
the Sun.
a.
v ∝ r−2
b.
v ∝ r−1
c.
d.
v ∝ r
e.
v ∝ r2
54.
Assume that when a
supermassive black hole accretes gas, approximately 20 percent of the accreted
mass is converted directly into energy, which is radiated away. If a quasar has
a luminosity of 1013 L⊙, then
what must be its mass accretion rate?
a.
1 M⊙ per year
b.
3.5 M⊙ per
year
c.
1 M⊙ per century
d.
3.5 M⊙ per century
e.
1 M⊙ per million years
55.
Which of the following
functions correctly illustrates the relation between mean density and black
hole mass?
a.
ρ ∝ M−2
b.
ρ ∝ M−1
c.
d.
ρ ∝ M
e.
ρ ∝ M2
56.
Scientists estimate
that the efficiency of mass accretion onto a supermassive black hole is about
15 percent. Compared with the energetic efficiency of the stellar fusion of
hydrogen into helium, the accretion is
a.
about 20 times more
efficient.
b.
about 20 times less
efficient.
c.
equally inefficient.
d.
twice as efficient.
e.
half as efficient.
57.
AGNs are most likely
powered by
a.
extremely dense star
clusters.
b.
accreting supermassive
black holes.
c.
ultradense molecular
clouds.
d.
decaying dark matter.
e.
supernova explosions.
58.
The unified model of
AGN suggests that quasars, Seyfert galaxies, and radio galaxies are
a.
unrelated, although
they are all very luminous galaxies at radio wavelengths.
b.
powered by similar mass
accretion rates onto supermassive black holes.
c.
driven by violent
mergers of two gas-rich spiral galaxies.
d.
similar phenomena but
viewed from different orientation angles.
e.
all powered by high
rates of star formation and supernova explosions.
59.
In most cases it is
impossible to observe the host galaxies of quasars because
a.
quasars outshine the
host galaxies by a few orders of magnitude.
b.
the supermassive black
holes have “eaten” all the stars in those galaxies.
c.
the host galaxies of
quasars have too much dark matter.
d.
the host galaxies of
quasars have too much obscuring dust.
e.
the galaxies hosting
quasars are much smaller than our own Milky Way.
60.
What happens to active
galaxies when their AGNs run out of fuel?
a.
The black holes
powering them collapse even further.
b.
They simply become
normal galaxies.
c.
They slowly dissipate
into clouds of gas and dust.
d.
They eventually pull in
material from farther out, starting the AGN process all over again.
e.
They explode as
gamma-ray bursts.
61.
Quasars were first
discovered in which region of the electromagnetic spectrum?
a.
X-ray
b.
gamma-ray
c.
radio
d.
infrared
e.
visible
62.
What do the broad
emission lines in quasar spectra tell astronomers about these objects?
a.
They are very far away.
b.
They are moving away
from us.
c.
They have rapid
internal motions.
d.
They are very dense.
e.
They have few heavy
elements.
.
63.
How do we know that
AGNs have sizes on the order of our Solar System?
a.
Quasars and Seyfert
galaxies are stellarlike sources.
b.
Their brightness varies
by factors of a few.
c.
The emission lines in
their spectra show gas rotating at speeds of thousands of km/s.
d.
Their brightness varies
on timescales ranging from hours to a day.
e.
We can measure their
angular size, which gives us the physical size when we know the distance.
64.
The formation of the
Solar System and the existence of AGNs both demonstrate the
a.
importance of how
luminosity varies with time.
b.
high efficiency of
nuclear fusion.
c.
importance of accretion
disks.
d.
importance of living in
the center of a galaxy.
e.
existence of dark
matter.
65.
In some radio galaxies,
we see only one side of the jet because
a.
the black hole produces
a jet in only one direction.
b.
of relativistic
beaming.
c.
the other side is
inside the black hole’s event horizon.
d.
of dust obscuration.
e.
of dark matter that
blocks the light from one side of the jet.
66.
We interpret the
presence of more AGNs in the past than today to indicate that
a.
there were fewer
galaxy-galaxy interactions in the past.
b.
there were more
galaxy-galaxy interactions in the past.
c.
supermassive black
holes were larger in the past.
d.
today’s AGNs are hidden
primarily by large amounts of cold gas and dust.
e.
AGNs had bigger central
black holes in the past.
67.
Quasars remain
unresolved sources, even with the best telescopic observations, because they
a.
are too luminous.
b.
occupy a very small
volume.
c.
are quite blue.
d.
produce copious amounts
of radio energy.
e.
host supermassive black
holes.
68.
Which of these
statements about quasars is false?
a.
Quasars are extremely
luminous.
b.
Quasars are rare in our
local vicinity.
c.
Quasars have high
brightnesses.
d.
Quasars are extremely
massive.
e.
Quasars are located at
the centers of some active galaxies.
69.
If a Seyfert galaxy’s
nucleus varies in brightness on the timescale of 10 hours, then what is the
approximate upper limit for the size of the emitting region?
a.
20 AU
b.
30 AU
c.
50 AU
d.
70 AU
e.
120 AU
70.
More luminous giant
galaxies tend to have __________ supermassive black holes at their centers.
a.
more massive
b.
radio quiet
c.
more luminous
d.
slower rotating
e.
less massive
SHORT ANSWER
1.
What determines the
three-dimensional shapes of galaxies?
2.
How do the current star
formation rates of spiral and elliptical galaxies compare?
3.
How did Hubble use his
tuning fork diagram to classify galaxies? Is there any significance to this
organization?
4.
How do we know that the
stellar disks in spiral galaxies are flat? How do we know that elliptical
galaxies are not flat?
5.
What were the positions
taken by Heber Curtis and Harlow Shapley in their “Great Debate,” and how were
both of them partially correct?
6.
How did Edwin Hubble
definitively prove that “spiral nebulae” were individual galaxies that were
separate from the Milky Way?
7.
The light curve of a
Cepheid variable star allows astronomers to infer its mean apparent magnitude
at 15.6 and the period of pulsation about 4.8 days. Utilizing the calibrated
relation between period and luminosity for Classical Cepheids, its absolute
magnitude is estimated at –3.6. What is the distance to that Cepheid star and,
implicitly, the distance to its host galaxy?
8.
Explain why the light
gray bands (labeled Radar, Parallax, etc.) that cover certain ranges of
distances in the figure shown below overlap with one another both at the beginning
and at the end?
9.
Name two “rungs” in the
distance ladder that let us estimate the value of the Hubble constant.
10.
Order the following
objects by the maximum distance they can be detected: Cepheid variables, RR
Lyrae stars, Type Ia supernovae, and low-mass main-sequence stars. Explain your
reasoning.
11.
Explain why the linear
Hubble’s law has no free term.
12.
The spectrum of a
galaxy is observed to have an Hα emission line at
a wavelength of 928.7 nm. What is its redshift? (Note that the rest wavelength
of the Hα emission line is 656.3 nm.)
13.
The spectrum of a
galaxy is observed to have an Hα emission line at
a wavelength of 856.3 nm. What is its distance if the Hubble constant is
assumed to be 70 km/s/Mpc? (Note that the rest wavelength of the Hα emission line is
656.3 nm.)
14.
What is the most likely
candidate for making up the dark matter in galaxies?
15.
How do we know that
many elliptical galaxies contain significant amounts of dark matter?
16.
What is plotted on a
rotation curve, and what can it tell us about a galaxy?
17.
If the rotational speed
of the gas in the disk of a spiral galaxy is 100 km/s at a distance of 26,000
light-years from its center, then what is the mass enclosed within this radius?
If the mass of luminous matter inside this radius is 5 billion M⊙ then what fraction of the galaxy’s mass is made of dark
matter (within that same radius)? (Hint: Recall the technique learned earlier
in Chapter 4.)
18.
Outside the dark matter
halo of a galaxy, how should the speed of an orbiting body such as a satellite
dwarf galaxy depend on its distance from the giant galaxy’s center?
19.
Estimate the total mass
enclosed within 100 kpc radius, based on the rotation curve shown in the figure
below. (Hint: Recall the technique learned earlier in Chapter 4.)
20.
Microquasars are scaled-down
versions of quasars, the former being powered by accretion onto stellar-sized
black holes, the material being provided by a companion star. The underlying
mechanism seems to be very similar in both microquasars and their supermassive
AGN. Typical microquasars have luminosities that are ten orders of magnitude
lower than ordinary quasars. What is the typical level of accretion rate in the
two cases?
21.
What are the main
components of an AGN?
22.
If there is a 4 million
M⊙ black hole at the center of our galaxy, why is our own
galaxy not an AGN?
23.
How do we explain that
“billions of galaxies are closer to Earth than is the nearest quasar”?
24.
Give three examples of
types of active galactic nuclei and give one reason why each is unique.
25.
What is the difference
between a Seyfert galaxy and a normal spiral galaxy?
26.
How do astronomers know
that AGNs are as small as our Solar System?
27.
How does the appearance
of an AGN depend on the viewing angle to the nucleus?
28.
What is the connection
between active galaxies and galactic mergers?
29.
Why is a higher
percentage of distant galaxies classified as AGNs compared with the percentage
of galaxies around us locally?
30.
If an AGN varies its
brightness on a timescale of 4 hours, then what is the size limit of the AGN
measured in AU?
|
For
The Students Who Need Grade ‘A’ In Their Studies
Hi, hope you are having a great
day…
We are a group of 24 writers
having profound expertise in Business and Computer Science subjects. We can
help you score A grade in your Accounting, Marketing, Finance, Economics,
Management, Mathematics, Statistics, Information System, System Modeling,
C++, Java Programming, Network Administration, Enterprise Administration,
Database, Web Design, Networking, Internetworking, Data warehouse etc…
We can also provide help with
Psychology, Nursing, Health, History, English Literature, Political Science,
Ethics, Humanity etc classes.
We can help with essays, term
papers, research papers, dissertation, Ilabs, mymatlab, Wileplus, quizzes,
exams, discussion questions etc.
You can expect:
We understand each student has
different requirement and we tend to treat each student according to his/her
satisfaction.
We will provide original
assignments, plagiarism free and to custom requirement.
We will always meet deadlines.
Our support will be 24/27, even
in holidays.
Our pricing will be fair.
We will do free revisions if
you want to make changes in provided work.
Email us for more information,
query and quote.
WHISPERHILLS@GMAIL.COM
|
No comments:
Post a Comment