Read Chapter 22
1.) Astronomers have found that dark matter resides in
a.) Spiral galaxies
b.) Elliptical galaxies
c.) Clusters of galaxies
d.) All of the above
e.) None of the above
2.) Suppose that you were to apply the equation M = r v2 / G
to our galaxy in order to calculate "the mass", and that you
used the orbital velocity (v) of a star that is located at a
distance (r) from the Galactic center.
From this formula, which mass would you be calculating?
a.) The mass of stars in the volume within the sphere that is centered
on the Galactic center and that has a radius of
r
b.) The mass of stars outside of the sphere that is centered
on the Galactic center and that has a radius of r
c.) The mass of stars along the path of length = r, which begins
at the Galactic center and ends at the location of the star
d.) None of the above
3.) How do astronomers measure the mass of a galaxy cluster?
a.) Measure the temperature of the intracluster gas, then calculate
the velocities of the gas atoms from it, then calculate the mass from
the velocities
b.) Measure the velocities of individual galaxies in the cluster, then
calculate the mass from the velocities
c.) Measure how effectively the cluster has bent the light coming from
more distant galaxies
d.) All of the above
e.) None of the above
4.) Although we do not know if dark matter is little
particles or big ones, let us
suppose that dark matter
is many, many subatomic particles spread evenly throughout
the space of the galaxy. Assume that the diameter
of the galaxy is 100,000 lightyears
(so the radius is
50,000 ly), and assume that the dark matter has 10 times
as much mass
as the regular matter in the Galaxy (let us
take the mass of the regular matter in the
Galaxy to
be 100 billion times the mass of the Sun and the Sun's
mass is 2.0 x 1033 grams)
a.) What is the density of dark matter in units of
grams per km3?
(For comparison, note
that a paperclip "weighs" about a gram.)
b.) Given the above assumption, how many grams of
dark matter reside within the
solar system? (For
the radius of the solar system, use the semi-major axis of
Pluto's orbit: 5.9 x 109 km .)
c.) Consider the mass of the Sun, Jupiter,
Earth, and Pluto.
(The Sun's mass is 2.0 x 1030 kg,
Jupiter's mass is 1.9 x 1027 kg,
the Earth's mass is 6.0 x 1024 kg, and
Pluto's mass is 1.3 x 1022 kg). Which of these
is
closest to the mass of the dark matter in the solar system?
d.) I have never seen any mention of dark matter in the solar system.
Why is the
solar system's dark matter unimportant?
e.) How can dark matter contribute a little to the mass of the
solar system, but a lot
to the mass of the galaxy?
5.) Which of these is on the list of hypothetical dark matter candidates?
a.) A diffuse gas of electrons
b.) Regular stars that were thrown out of the Galactic disk
c.) Planets, brown dwarfs, black dwarfs
d.) All of the above
e.) None of the above
6.) How does/did dark matter affect our galaxy?
a.) It has no effects on our galaxy
b.) It attracted the material that would eventually form
the observable part of our galaxy
c.) It helps push the material in our galaxy out to further distances
from the Galactic center
d.) All of the above
e.) None of the above
7.) According to models of the universe's evolution, the
extremely dense regions where superclusters are
a.) Are currently gravitationally attracting nearby material
b.) Have been been extremely dense since the beginning of time
c.) Are impossible to reproduce with computer simulations
d.) All of the above
e.) None of the above
8.) If you were to make a 3 dimensional map of the observable part of the
universe:
a.) Your map would have deserts where there are very few galaxy clusters
b.) Your map would have regions where galaxy clusters lined up along
a curvy line or warped-sheet shape
c.) Both of the above
d.) Neither of the above
9.)
a.) How does the amount of dark matter in the universe
affect the universe's final fate?
b.) Given our current understanding of the universe, what is
the universe's final fate?
10.)
One of the traditional models for the universe is the
"recollapsing universe". How does the data on distant
supernova explosions rule-out the "recollapsing universe" model?