Questions for Chapter 21
- What is
do we mean by galaxy evolution?
describe the starting assumptions for galaxy formation, and how models
suggest that these starting conditions can lead to the formation of a
two ways in which conditions in a protogalactic cloud might lead to the
birth of an elliptical rather than a spiral galaxy.
for the large variety of sizes (2) and types (3) of galaxies by describing
their formation and evolution.
happens when two galaxies collide? How might elliptical galaxies form from
collisions of spiral galaxies? What evidence supports the idea that galaxy
collisions sometimes occur?
explain why we expect collisions between galaxies to be relatively common,
while collisions between stars are extremely rare. Why should galaxy
collisions have been more common in the past than they are today?
- What is
a starburst galaxy? How do observations of starbursts help us understand
why the stars in elliptical galaxies are so old?
explain why starburst galaxies often appear ordinary when they are
observed in visible light but extraordinary when they are observed in
is a galactic wind? What causes it? How is it similar to a superbubble in
the Milky Way, and how is it different?
describe the discovery of quasars. What evidence convinced astronomers
that the high redshifts of quasars really do imply great distances? Why
can we learn more about quasars by studying nearby active galaxies and radio
at least three definitely observed properties of quasars and indicate
briefly how one theory fits them.
the supermassive black hole model for the energy output of quasars and
other active galactic nuclei. What evidence suggests that such black holes
- What is
this? The red shows radio waves.
is a radio galaxy? Describe jets and radio lobes. Why do we think that the
ultimate energy sources of radio galaxies lie in quasar like galactic
one energy generating source for radio galaxies and /or active galaxies
and explain how it results in the observed phenomena.
Milky Way has a black hole at its center. Why isn't it an AGN?
- In an
active galaxy where does the x-ray, ultraviolet, visible, infrared and
radio radiation come from?
- This is a
spectrum from a galaxy. Can you tell what might be going on?
Decide whether the statement makes sense (or is clearly
true) or does not make sense (or is clearly false). Explain clearly; not all
these have definitive answers, so your explanation is more important than your
that are more than 10 billion years old are too far away for us to see
even with our most powerful telescopes.
galaxies are more likely to form in denser regions of space.
- If the
Andromeda Galaxy someday collides and merges with the Milky Way, the
resulting galaxy may be elliptical
9645 is a starburst galaxy that has been forming stars at the same furious
pace for some 10 billion years.
energy from supernova explosions can drive a large proportion of the
interstellar gas out of a small galaxy.
proved that quasar 3C 473 contains a supermassive black hole when they
discovered that its center is completely dark,
- The black
hole at the center of our own galaxy may once have powered an active
galaxies emit only radio waves and no visible light.
of quasar light can tell us about intergalactic clouds that might
otherwise remain invisible.