The Hidden Lives of Galaxies - Answer Key for Activities
1. c. {Sombrero Galaxy} With a bright halo of stars and a large central bulge of stars, it looks like a hat.
2. d. {Whirlpool Galaxy} It looks like a whirlpool in the ocean or water going down a drain.
3. a. {Polar Ring Galaxy} It contains an inner central disk of old stars and an outer ring of younger stars giving it the appearance of a ring on a ringer.
4. b. {Siamese Twins Galaxy} It shows how gravitational pull sometimes causes two galaxies to collide or brush against each other, giving the appearance of two joined bodies.
Activity #5 - Open Clusters versus Globular ClustersAnswers should include the following similarities: both contain numerous red stars, and colored stars. Globular clusters contain older stars. Stars near the center tend to be brighter. The stars appear to be gravitating towards the center of the cluster, like bees swarming around the hive. The cluster contains hundreds to thousands of stars. The stars appear closer together. Open cluster stars appear scattered. The blue stars are more visible. Open clusters contain hundreds of stars, many which are bright, young, and blue. Activity #6a - Evidence for Hidden Mass
1. There are 9 Solar System planets presented on the graph. The planets from the closest to Sun to the furthest from the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
Using the graph, the velocities of the solar system planets, from the lowest value to the highest value, are approximately 48, 35, 30, 24, 13, 10, 7, 5, 4 km s-1.
Using the graph, the distances of the planets from the Sun are, from least to greatest, 0, 110, 150, 250, 800, 1500, 2800, 4500, 6000 million km.
In general, the further the planet is away from the Sun the slower the velocity. The closer the planet is to the Sun the faster the velocity.
2. Answers should include fact that velocities first increase with increasing distance. At distances larger than 10 kpc, the velocity becomes constant with increasing distance.
Activty #6b - Extension: Weighing a Galaxy1. The calculation for each of the planets should result in a value for M of
2. The mass increases as the distance from the center of the galaxy increases. This is because stars move under the gravitational influence of all the matter within their orbit.
Distance (kpc) | Velocity | Mass (kg) |
5.0 | 95.0 | 2.1 x 1040 |
10.0 | 110.0 | 5.6 x 1040 |
15.0 | 110.0 | 8.4 x 1040 |
So stars at greater distances move under the influence of more mass than stars closer to the center.
The best estimate for the mass of the galaxy is the one which includes the most amount of mass. From this calculation, the largest value is