HOMEWORK#7
Cosmology
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15.1-15.3— Review & Discussion 1,4,5,6,8,10. Self Test 1 & 4
Chapter 17 Review & Discussion 1-5, 7,9. Self Test 1-12
15.1-15.3 Review & Discussion
1.Distinguish among the various types of serial galaxies.
A. Barred spiral galaxies have an elongated central bulge as compared to regular spiral
galaxies. Sa and SBa galaxies have large bulges and tightly wrapped spiral arms. Sb and
SBb have somewhat smaller bulges and less tightly wrapped arms. Sc and SBc have the
smallest bulges and the most loosely wrapped arms
4. How does the Tully Fisher relation allow astronomers to measure the distances to galaxies?
A. By measuring the amount of broadening in emission lines, you can determine a galaxy’s
rotation. One that is know , you can then determine luminosity, comparing a galaxy’s
luminosity with its apparent brightness gives us its distance
5. What is the Virgo Cluster?
A. The nearest large galaxy cluster to the Local Group, it also houses 2500 galaxies, much
more than our own
6. What is Hubble’s Law, adn how is it used by astronomers to measure distances to galaxies?
A. Hubble’s law relates the observed velocity of recession of a galaxy to its distance from
us. The velocity of recession of a galaxy is directly proportional to its distance away. By
using Hubbles’ law we can derive the distance to a remote object simply by measuring
the objects recessional velocity and dividing by Hubble’s Constant (70km/s/mpc)
8. Why do astronomers prefer to speak in terms of redshirts rather than distances to faraway
objects?
A. Due to is being a directly observable property of an object, whereas distance is derived
from a redshift with use of Hubble’s Constant, whose value is not accurately known
10. What is the evidence that the radio lobes of some active galaxies consist of material ejected
from the galaxy’s nucleus?
A. Centaurs A, of which is a member of a small cluster of galaxies, Its radio lobes are
roughly symmetrical, jutting out from the center of the galaxy and perpendicular to the
dust lane, suggesting that they consist of materials ejected in opposite directions from
the galactic nucleus.
Self Test
1.Most galaxies are spiral like the Milky Way (T/F) False, most galaxies are not large spirals,
most usual galaxies types are dwarf elliptical and dwarf irregulars
4. Type I supernovae can be used to determine distances to galaxies (T/F)
True, Type I Supernovae can be used to determine distances to galaxies due to that they are
formed by white dwarfs that explored when the reach a uniform accelerated mass, the
supernova peak luminosity is thought to be very consistent
Chapter 17 Review & Discussion
1. What evidence do we have that there is no structure in the universe on very large scales?
How large is “very large”?
a. The redshift surveys of galaxy location show no structure larger than about
100-200 Mpc
2. What is the cosmological principle?
a. The cosmological principle states that the universe is both homogeneous and
isotropic
3. What is Olbers paradox? How is it resolved?
a. Olber’s paradox states that the whole sky should be as bright at the surface of a
star if the universe is homogeneous, isotropic, infinite and unchanging, it is
resolved because the universe is neither infinite nor unchanging.
4. Explain how an accurate measure of Hubble's constant can lead to an estimate of the age
of the universe.
a. By dividing the distance travelled by galaxies by the rate (H0), one can determine
time (age)
5. WHy isn’t it correct to say that the expansion of the universe involves galaxies flying
outward into empty space?
a. Due to the expansion of the universe is the expansion of space itself. There is no
actual “empty space”, for the universe to expand into
7. Why does the cosmological redshift relate to the expansion of the universe?
A. In cosmological redshift, the wavelength at which the radiation is originally emitted in
lengthened as it traveled through expanding space, of which this results from the
expansion of space itself and not from the motion of an individual body
9. Why are observations of the distance supernovae so important to cosmology?
A. They type 1 distance supernovae indicate the behavior of the distant galaxies. This
information shows that he universe appears to be expanding and an accelerating rate
Self Test
1. False, deep surveys of the universe roughly show 10,000 galaxies to the 24 magnitude.
2. False, if the universe had an edhe, it would just simply be the edge of our observable
universe, as the edge just simply marks the dividing line between locations that
earthlings can see and locations we can not.
3. False, the Hubble law implies that if the universe is static and unchanging there is no
correlation between distance and velocity
4. True, a cosmological redshift is the expansion that stretches light traveling through
space
5. True, due to the fact that the usnicerse is expansind, and that expansi stretchers light
traveling through space, the greater the red shift the greater the distance the light has
travaled
6. False, the density of dark matter is not even .1 of a solar masses per cubis parsex, it is an
extremely low density
7. True, the cosmic microwave background is the left over radiation from the BIG bang or
the time when it all began.
8. True, the theory of imlation proposes a period of extremely rapdu expansion of the
universe during its first few moments , like the big bang theory.
9. The finite age of the universe, olbers paradox is a phtometric paradox thaty consist due
to the fact that if the universe is filled with stars and infinite in space and time, then the
brightness of the sky, showuold be equal to the brightness of the solar disk
10. Exploding white dwarfs
11. The universe is infinite in extent and will expand forever
12. Greater than bathe age of the Milky Way galaxy