Collisions LessonOverviewGalaxies are observed to occur in a variety of shapes. They can generally be classified as either spiral or elliptical, with different patterns seen in spiral galaxies. The purpose of this lesson is to explore the role that collisions and near collisions of galaxies play in determining the shape of galaxies. Students will model the collision of disk shaped and spherically shaped galaxies.Preparation and MaterialsThe teacher should be familiar with the GalaxSee application (for those unfamiliar with this software, there is an online tutorial), have it loaded on a PowerMac or PC, and have some means of displaying the monitor to the class.As GalaxSee is only designed to generate a single galaxy, students will need a spreadsheet to either copy and paste galaxy data, or create their own. Helper spreadsheets are provided for Excel. ObjectivesStudents will
StandardsThis lesson fulfills portions of the following standards and curriculum guidelines:
Activities
NOTE: Alternatively, you can create a disk galaxy in GalaxSee, open that in a spreadsheet, copy and paste the galaxy data to create two galaxies, and offset the position and velocity in you spreadsheet.
Note: As the students try to create galaxies which contain the same amount of mass in a smaller physical space, they will have to use a smaller time step to reduce numerical error. Make sure the students are keeping track of the energy in the info window. For more information about detecting and controlling error, see the section about the info window in the GalaxSee tutorial. Discussion of the SimulationGalaxies are extremely large objects. They are so large that in a close interaction, the near side of the galaxy will be pulled towards the other object more strongly than the far side, stretching the object. Ask the students what would happen if you pulled an object while it was spinning.Can your students give any examples of objects that are pulled and spun at the same time (A taffy machine)? Can your students give any examples of where an object in space stretches something by pulling more on a close side than the far side (Ocean tides, the break-up of the comet Shoemaker-Levy 9) Discussion of ObservationAsk the students to describe how galaxy interactions might produce the shapes they observe in images of galaxies. While spiral structure is thought to be due to the collision of two disk galaxies, how might irregular galaxies be formed?Assign them to write a clear and accurate report of what they observed and modeled. Emphasize that it is important that they know what software was used, and what parameters were set. Be sure to go through the setup procedure again so that they can record this information. CollaborationAfter they have polished their reports, instruct them to prepare and post a note to WebCaMILE for another group of students to see. If possible, have the other group of students attempt to repeat the experiment as described in the note, verify the findings of the first group, and provide feedback about their methods and conclusions.Encourage both groups to ask questions of each other's procedure and observations. If another group of students is not available, you could split one class into two large groups and require them to communicate only through writing. ExtensionsFurther ExperimentationIf disk galaxies are formed by rotation, and spirals by collisions of two disks, why is it that many of the oldest galaxies observed tend to be ellipticals? Have the students collide more than 2 galaxies. What is the result of mergers of multiple galaxies?Thinking HarderBy now students should know the theory that rotation causes flattening, and that collisions of two spinning disk galaxies cause spiral formation. Ask the students how galaxies start spinning in the first place. Compare two possibilities. One, galaxies collide, causing rotation. Two, galaxies were formed as mass spread out over a very large area collapsed under its own gravity, and in the process, any small amount of rotation would increase as the object got smaller, like a ice skater pulling his/her arms in. How would the student try to set up observations and models to compare these possiblities?Go to GalaxSee Curriculum Resources Please direct questions and comments about this page to WebMaster@shodor.org © Copyright 1996 The Shodor Education Foundation, Inc. |