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Here it is my proyect for Phy 381C. I was trying to simulate the merger of two galaxies using th e particle mesh method with a multigrid solver to find the solution of the Poisson equationi. I had a lot of problems finding one stable galaxy. You can find a copy of my term paper in postcript called Me rgers of Galaxies and you can see some plots made with Explorer of how the galaxy it is NOT stable: t=1 , t=2 , t=3 ,in these first steps you can see how the core of galaxy change in a strange way.This produces that the particles on the disk go away ( there is no enough mass inside their orbits ) are they make a ring : t=4 , t=5 , t=6 , t=7 , t=8 , t=9 , t=10 At the final step the ring is clearly visible.

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