1.) How is the evolution of a spiral galaxy similar to that
of a protostar?
a.) In both cases a cloud of gas gravitationally contracts
b.) Early on, the material cools by radiation
c.) Both "spin-up"
d.) All of the above
e.) None of the above
Answer: d
2.) Why do some protogalaxies evolve into spiral galaxies
while others evolve into elliptical galaxies?
a.) Because the amount of angular momentum differs between
protogalaxies
b.) Because the fraction of metals atoms in the gas differs between
protogalaxies
c.) Both of the above
d.) None of the above
Answer: a
3.) How do astronomers explain the existence of irregular galaxies?
a.) As two galaxies are merging, they look like an irregular galaxy
b.) Before a protogalaxy has finished forming its disk, it looks irregular
c.) Galaxies with strong Active Galactic Nuclei look irregular
d.) All of the above
e.) None of the above
Answer: a
4.)
a.) What role do mergers play in making spiral galaxies?
Answer: Astronomers think that protogalaxies can merge, resulting
in larger protogalaxies
that eventually evolve into galaxies.
Some of the resulting galaxies are spiral galaxies.
b.) What role do mergers play in making elliptical galaxies?
Answer: In addition to the merging of protogalaxies discussed above,
astronomers think that
mergers play another role in making elliptical
galaxies. When fully formed galaxies merge,
sometimes the resulting
galaxy is an elliptical galaxy.
c.) What role do collisions or mergers play in making irregular galaxies?
Answer: While galaxies are colliding or merging, they look irregular.
d.) What role do collisions or mergers play in making starbursts?
Answer: When galaxies collide or merge, some of their interstellar
gas becomes compressed.
In regions where the gas becomes very dense,
new stars form.
So, the collision or merger
leads to an epoch of star birth, called a
starburst.
5.)
a.)
What is a galactic wind?
Answer: Clustered supernovae and
stellar winds blow very large bubbles.
If a bubble has
enough energy, it can
pop through the galactic disk and expand
into the halo. Material flows
from the disk into the halo and even into intergalactic space.
This flowing material
(i.e. hot, ionized interstellar gas) is called a galactic wind.
b.)
What causes a galactic wind?
Answer: a stellar wind is due to the bursting of a superbubble
which was blown by clustered
supernovae and steller winds
6.)
a.) How is a galactic wind similar to a superbubble in the
Milky Way galaxy?
Answer: The similarity between a galactic wind and a
superbubble is that both are gas
(usually hot and ionized) which was heated, ionized, and pushed around
by clusters of supernovae
(plural of supernova) and stellar winds. Also, the wind is just the
aftermath of an erupted
superbubble.
b.) How is a galactic wind different from a superbubble in
the Milky Way galaxy?
Answer: A superbubble hasn't yet broken open and dispersed
its hot gas into the halo and
intergalactic space.
Also, we discussed galactic winds in the context of
starburst galaxies,
not normal galaxies. The reason is
that it takes a lot of supernova explosions to blow a
superbubble that is big enough to burst.
7.) Which type of galaxy has
a supermassive black hole and extremely bright accretion disk
in its center?
a.) A quasar
b.) A radio galaxy
c.) A galaxy having an Active Galactic Nuclei
d.) All of the above
e.) None of the above
Answer: d
8.) Describe the jets and lobes of a radio galaxy
Answer:
The centers of
radio galaxies shoot out powerful jets.
These jets are streams of
ionized material (i.e. electrons and ions)
travelling at nearly the speed of light.
At the far
end of a jet, the jet material is crashing
into intergalactic gas. There, much of the jet material
splashes back, to create a "lobe".
In the lobes, electrons and protons spiral around the
magnetic fields and so produce radio frequency light.
Galaxies whose jets and lobes emit
strong radio frequency light are called "radio galaxies".
9.) Why do we think that the ultimate
energy source for a radio galaxy is material
falling into a huge black hole?
Answer:
Astronomers think this because the luminosities of radio galaxies are
so large that they
require a mechanism such as material falling toward
a black hole to power them. Material falling
toward a black hole
releases energy because during the fall, gravitational potential
energy is
converted into kinetic energy, then into thermal energy,
then into radiative energy. Also
astronomers
have seen some active galactic nuclei that have core-jet-lobe
structures similar to those of radio galaxies.
Active galactic
nuclei are viewed at angles where we can sometimes see that stars
near the center are
orbiting the center very rapidly. From the velocity and distance,
the mass of the object in the center
can be calculated. The
mass is on the order of a billion solar masses. A black hole can
be this size.
There is no other object that can have that much
mass in such a small space.
10.) What sort of observational evidence supports the
idea that supermassive black holes exist?
Answer: Astronomers can see material near a black hole
orbiting the black hole at a very fast speed.
By using the general form
of Kepler's 3rd law, they calculate the mass. The calculated
mass is much larger
than expected for a normal star. And, the
size of the region is much smaller than would be necessary
for a cluster of stars. So, the only way for there to be such a
large mass in such a small space is for
there to be a black hole in the space.
11.) Regarding the gas clouds residing between the Milky Way
and the most distant observable quasars:
a.) Usually the clouds that are furthest from the Milky Way have the least
amounts of neutral hydrogen gas
b.) Usually the clouds that are furthest from the Milky Way have the smallest
fractions of metal atoms
c.) Usually the clouds that are furthest from the Milky Way have the least
redshifted hydrogen absorption lines
d.) All of the above
e.) None of the above
Answer: b