Use these questions to test your understanding. If you get them wrong, you will be linked back to the relevant part of the notes. 

Be sure you study them thoroughly (don't just get a quick fix for your mistake) so your overall understanding is improved.

1. We know about dark matter

   a. because it blocks our view in certain directions

   b. because it can be seen in other galaxies but not in the Milky Way

   c. because black holes left by massive stars are sometimes visible in the X-ray

   d. from the rotation curves of galaxies that show mass outside the region of stars

   e. because the planets seem to orbit the sun faster than the mass of the sun alone would require

2. Why does the rotation curve of a galaxy increase with increasing distance near the galaxy's center?

   a. the encircled mass increases so fast that gravity increases with radius

   b. the stars are exploding outwards from the center, thus showing the high speeds 

   c. most of a galaxy's mass is in the center

   d. because the center rotates like a rigid wheel or Merry-Go-Round

   e. because of the effects of active galaxy nuclei

3. What is the evidence there is dark matter beyond the disks of spiral galaxies?

   a. inner disk stars orbit faster than the mass due to stars and gas can explain

   b. infrared telescopes detect mass beyond the galaxy disks

   c. the stellar mass distribution does not account for the rotation curve of the galaxies

   d. disk stars orbit faster than stars in the galactic centers

   e. regions outside the disks obscure the light of galaxies behind them

4. The outer part of the rotation curve of a galaxy is flat; this fact indicates that

   a. practically all the mass of the galaxy is within the radius where the curve flattens out

   b. where the curve is flat, the encircled mass increases with increasing distance from the center

   c. Newton's law of gravity is wrong

   d. there is a supermassive black hole at the center of the galaxy

   e. the galaxy is still in the process of forming

5. We think that either dark matter is in the form of low mass brown dwarfs and wandering planets, or

     a. Newton's Law of gravitation is wrong

     b. the Universe is filled with an undetected type of nuclear particle

     c. the galaxy rotation curves are distorted

     d. we are overestimating the accuracy of the velocity measurements in galaxies

     e. the spectral lines suffer graviational redshift due to Einstein's law of relativity

6. Most of the mass of the Milky Way is

        a. in its stars

        b. in the supermassive black hole in its center

        c. in the interstellar gas

        d. in a.) through c.)

        e. in the form of dark matter

7. The discovery of large amounts of dark matter outside the visible diameter of galaxies is consistent with

        a. the active nuclei arising from nuclear black holes

        b. the necessity for galaxies to be larger than they appear to account for their high collision rate in the early Universe

        c. the presence of globular clusters in the halo of the Milky Way

        d. ongoing star formation we see at the fringes of the Milky Way

        e. the dimming of background galaxies near large, nearby galaxies like Andromeda