Chapter 15 Quiz: Olivia Ward

1. What are the three major types of galaxies?
   
   The three major types of galaxies are spiral galaxies, elliptical galaxies, and irregular galaxies. Spiral galaxies have a rotating disk that contains stars, gas, and dust, as well as a bulge that is home to its star concentration. Elliptical galaxies which can vary in shape and size, but contain stars that are much older than the ones in a spiral galaxy. Irregular galaxies do not have a regular or symmetrical structure.
   
2. How are galaxies grouped together?
   
   Spiral galaxies are found in groups of other galaxies, with up to a few dozen galaxies per group. Elliptical galaxies are commonly found in huge clusters of galaxies, with hundreds of thousands of galaxies in a group.
   
3. How do we measure the distances to galaxies?
   
   We can measure the distance to galaxies by using parallax and its relationships to brightness, luminosity, and distance, as well as by studying Cepheid variable stars. White dwarf supernovae can also be used as standard candles.
   
4. What is Hubble's law?
   
   All objects in deep space are redshifted and moving away from a central point. Hubble's law is the following equation: Velocity = H0 X distance
   
   
5. How do distance measurements tell us the age of the universe?
   
   Hubble's constant tell us the age of the universe because it relates velocities and distances of all galaxies. These figures tell us how long it has taken for galaxies to reach their current distance and position in space.
   
6. How do we observe the life histories of galaxies?
   
   Deep observations show us how distant galaxies looked when they were much younger.
   
7. How did galaxies form?
   
   Matter originally filled all of space almost uniformly.  Gravity of denser regions pulled in the surrounding matter. Denser regions contracted, forming protogalactic clouds. H and He gases in these clouds formed the first stars. Supernova explosion from the first stars kept much of the gas from forming stars. Leftover gas settled into a spinning disk.
   
8. Why do galaxies differ?
   
   Galaxies differ because of conditions in the protogalactic cloud. These conditions can determine the size of the resulting disk, as well as the density and star population. Galaxies also differ because of collisions which have caused galaxies to take on different forms. For example, two spiral galaxies can collide to create an elliptical galaxy.
   
9. What are quasars?
   
   Quasars are the most luminous examples of active galactic nuclei. Quasars powerfully radiate energy over a very wide range of wavelengths, indicating that they contain matter with a wide range of temperature.
   
10. What is the power source for quasars and other active galactic nuclei?
    Energy from a black hole is the power source for quasars and other active galactic nuclei.The gravitational potential energy of matter falling into a black hole turns into kinetic energy. Friction in the accretion disk turns kinetic energy into thermal energy. Jets are also thought to come from the twisting of magnetic field in the inner part of the accretion disk.