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1
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- Question 1 (1 point) Observations of galaxies and clusters
of galaxies indicate that roughly ____ percent of the universe is dark
matter.
a.5%b.25%c.50%d.75%e. 95%
- You have to look this one up, but it is a number you should know.
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2
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- Question 2 (1 point) An elliptical galaxy could
- a. evolve into an irregular galaxy when it has used up all of its gas
and dust.
- b. be formed from the collision and merger of spiral galaxies.
- c. become a starburst galaxy if it were to move through the hot
intergalactic medium of a cluster.
- d. evolve from a single spiral galaxy when that spiral used up all of
its gas and dust.
- Elliptical galaxies have already used up their gas and dust, and it is
thought they can be formed from spiral mergers.
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3
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- Question 3 (1 point) If Galaxy A is four times more distant
than Galaxy B, then according to the Hubble Law, the recessional
velocity of Galaxy A is larger than that of Galaxy B by what factor?
- Four. The Hubble Law (v = Hd) is
linear. Double the distance, the
velocity must also be doubled.
You can also solve this explicitly using the equation twice, once
for galaxy A, once for B, and taking the ratio to show that VA/VB
= dA/dB = 4 (H cancels out since it is a
constant).
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4
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- Question 4 ( 1 point) If a galaxy has a radial velocity
(redshift) of 5000 km/s, how far away is it? Assume a Hubble Constant of
70 km/s/Mpc.
a.7 Mpc b.20 Mpc c.49 Mpc d.71 Mpc e.100 Mpc
- V = Hxd, so d = v/H = 5000 km/s/70 km/s/Mpc – the km/s cancel out to
give 5000/70 Mpc = 71 Mpc
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Notes