Chelsea Esposito's Quiz

Chelsea Esposito

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 x 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 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 the observations holds that supermassive black holes are the
power source.