Q Part 1: Suppose the amount of mass in a black hole doubles, does the event horizon change? If so, does it grow, shrink, or stay the same size? And what physical force limits the growth of supermassive black holes? Part 2: Assume that the distance from one edge of the Milky Way Galaxy to the other is 1 cm, with this same scale how far away is the Andromeda Galaxy? Why do astronomers believe that gravitation in the universe is dominated by dark matter?