Chapter 28 The Evolution and Distribution of Galaxies
Chapter 28 The Evolution and Distribution of Galaxies
28.7 Collaborative Group Activities, Questions and Exercises
Collaborative Group Activities
- Suppose you developed a theory to account for the evolution of a large city such as New York City. Have your group discuss whether it would resemble the development of structure in the universe (as we have described it in this chapter). What elements of your model for New York City resemble the astronomers’ model for the growth of structure in the universe? Which elements do not match?
- Most astronomers believe that dark matter exists and is a large fraction of the total matter in the universe. At the same time, most astronomers do not believe that UFOs are evidence that we are being visited by aliens from another world. Yet astronomers have never actually seen either dark matter or a UFO. Why do you think one idea is widely accepted by scientists and the other is not? Which idea do you think is more believable? Give your reasoning.
- Someone in your group describes the redshift surveys of galaxies to a friend, who says he’s never heard of a bigger waste of effort. Who cares, he asks, about the large-scale structure of the universe? What is your group’s reaction, and what reasons could you come up with for putting money into figuring out how the universe is organized?
- The leader of a small but very wealthy country is obsessed by maps. She has put together a fabulous collection of Earth maps, purchased all the maps of other planets that astronomers have assembled, and now wants to commission the best possible map of the entire universe. Your group is selected to advise her. What sort of instruments and surveys should she invest in to produce a good map of the cosmos? Be as specific as you can.
- Download a high-resolution image of a rich galaxy cluster from the Hubble Space Telescope (see the list of gravitational lens news stories in the “For Further Exploration” section). See if your group can work together to identify gravitational arcs, the images of distant background galaxies distorted by the mass of the cluster. How many can you find? Can you identify any multiple images of the same background galaxy? (If anyone in the group gets really interested, there was a Citizen Science project called Spacewarps, where you could have help astronomers identify gravitational lenses on their images: https://spacewarps.org There are other citizen science project available at: https://www.zooniverse.org/projects?page=1&status=live .)
- You get so excited about gravitational lensing that you begin to talk about it with an intelligent friend who has not yet taken an astronomy course. After hearing you out, this friend starts to worry. He says, “If gravitational lenses can distort quasar images, sometimes creating multiple, or ghost, images of the same object, then how can we trust any point of light in the sky to be real? Maybe many of the stars we see are just ghost images or lensed images too!” Have your gro