Galaxy Collisions
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# Supplemental Exercise: Galaxy Collisions

Astronomer Chris Mihos and his colleagues from Case Western Reserve University and the University of Oregon have written a free Java applet that simulates interacting galaxies. Go to their web site by clicking here.

Click Applet to launch the applet. A new window will open, and the program will take a moment to load. Click Controls to launch a small window describing the applet's controls. Change the angles of the galaxies with respect to each other by clicking the dials with the left or right mouse buttons. Change their separation distance by changing the "Peri" variable. "Peri" is measured in kiloparsecs (kpc); 1 kpc = 3,200 light-years. Change the mass of the red galaxy with respect to the green galaxy by changing "Red Galaxy Mass."

If you don't see both galaxies in the window to the right, click Reset. To start the simulation, click Start. You will see the two galaxies interact in the right side of the window. The window also shows the elapsed time in millions of years and the separation of the galaxies in kiloparsecs (1 kiloparsec = 1000 parsecs = 3000 light-years). The graph at the bottom shows the separation (pink) and the relative velocity of the galaxies (blue) as a function of time.

 Supplemental Exercise 1. Change the angles, initial separation, and initial masses of the galaxies. Also try checking "friction," which turns on friction in the simulation, and "big halos," which gives the galaxies large dark matter haloes. Experiment by changing some of the parameters. Have fun!

 Supplemental Question 1. What are the most important parameters for determining what a galaxy interaction will look like?

 Supplemental Question 2. Can you design a simulation that will give you an output that looks like the picture above? What parameters do you need to use?