Quiz
1.
What are the three major types of galaxies?
Spiral galaxies, elliptical galaxies, and
irregular galaxies. Spirals have both disk and spheroidal components; ellipticals
have no disk.
2.
How are galaxies grouped together?
Spiral galaxies tend to collect into groups
of up to a few dozen galaxies. Elliptical galaxies are more common in large
clusters containing hundreds to thousands of galaxies.
3.
How do we measure the distances to galaxies?
The distance measurement chain begins with
parallax measurements that build on radar ranging in our solar system.Using
parallax and the relationship between luminosity, distance, and brightness, we
can calibrate a series of standard candles. We can measure distances greater
than 10 billion light-years using white dwarf supernovae as standard candles.
4.
What is Hubble's law?
The faster a galaxy is moving away from us,
the greater its distance:
velocity = H0 ´ distance
5.
How do distance measurements tell us the age of
the universe?
Measuring a galaxy’s distance and speed
allows us to figure out how long the galaxy took to reach its current distance.
Measuring Hubble’s constant tells us that amount of time: about 14 billion years.
6.
How do we observe the life histories of
galaxies?
Deep observations of the universe are
showing us the history of galaxies because we are seeing galaxies as they were
at different ages.
7.
How did galaxies form?
Our best models for galaxy formation assume
that gravity made galaxies out of regions of the early universe that were
slightly denser than their surroundings.
8.
How do galaxies differ?
Some of the differences between galaxies
may arise from the conditions in their protogalactic clouds. Collisions can
also play a major role because they can transform two spiral galaxies into an
elliptical galaxy.
9.
What are quasars?
Active galactic nuclei are very bright
objects seen in the centers of some galaxies, and quasars are the most luminous
type.
10. What
is the power source for quasars and other active galactic nuclei?
The only model that adequately explains our
observations holds that supermassive black holes are the power source.
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