APAS 1020

Quiz #4

November 7, 1997

 

  1. (1) In the tuning fork diagram (circle the correct answer)
  1. Evolution proceeds to the right from ellipticals to spirals
  2. Evolution proceeds to the left from spirals to ellipticals.
  3. There is no evolutionary sequence contained in the diagram.
  1. (1) What is the evidence that "genesis" has not stopped, creation is on-going, and that galaxies are still in the process of evolution and change.

There are many pieces of evidence including super novae creation of elements, new stars forming in gaseous nebulae, and collisions, merging, and gobbling-up of galaxies. The most significant discovery in recent years in this area is formation of new types and structures of galaxies through collisions and the consequent burst of new star formation.

  1. (1) Why are huge elliptical galaxies are found in the centers of rich clusters of galaxies such as M87 in the Virgo cluster?

The centers of these rich galaxies have high concentrations of galaxies and therefore frequent collisions among adjacent galaxies. The galaxy in the center grows both in size and in gravitation, therefore pulling more and more smaller galaxies into itself.

4. (2) How do galactic sound waves produce stars? Illustrate your answer with a diagram.

Spiral density waves are simply sound waves (compression and rarefaction) waves which move at the speed of sound in the gas of the galaxy. In the regions of compression, new star formation is occurring. The regions of rarefaction correspond to the i nter-arm regions.

  1. (2) How do collisions between galaxies produce massive black holes in the nuclei of elliptical galaxies

Illustrate your answer with a diagram.

Collisions scatter and disrupt the orderly stable orbits of stars around the nucleus of the galaxy, causing some stars to fall into the nucleus while other are sent flying out of the galaxy. Those that fall in (about half) come together to form the central black hole.

6. (1) Why do we not expect an elliptical galaxy in the center of the Local Group.

We are not a rich cluster of galaxies. There is no "center" of the local group and no increase in the concentration of galaxies.

7. (2) What is the source of the gigantic galactic arcs that are found deep in space? Illustrate your answer with a diagram.

Bending (refraction) of light of distant galaxies due to the curvature of space, as first predicted by Einstein in his General Theory of Relativity.

  1. (6) What is the dominant Population Type in each of the following?
  1. Elliptical galaxies_____II
  2. Galactic nuclei_____II
  3. Globular clusters____II_
  4. The very first galaxies to appear in the universe_____II
  5. Spiral arms_____I
  6. Clusters of O&B stars_____I

9. (1) Why do globular clusters have the lowest heavy element abundances of any object in the galaxy?

They were formed before many supernovae scattered heavy elements in the interstellar gas.

10. (2) What are the two major roles that supernovae have in the formation of new stars?

  1. Production and scattering of heavy elements
  2. Shock waves that cause collapse of gas clouds and production of stars

11. (2) What are two astronomical phenomena that have played major roles in the formation of life on the earth, i.e. why are we "starstuff"?

  1. Production and scattering of C,O, N atoms
  2. Formation of complex molecules in the interstellar medium that may have dropped into the warm primordial oceans of earth.
  3. Collisions of asteroids and comets with the earth which has influenced life and evolution.
  4. Collisions of comets with the earth that have produced our oceans
  5. Production of cosmic rays which may have speeded up evolutionary change.
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