This sequence shows a parabolic encounter and subsequent merger between two disk galaxies with a 3:1 mass ratio. The galaxies orbit each other in a clockwise direction, and the orbit plane is viewed face-on. The larger disk lies in the orbit plane but spins in a counter-clockwise direction, while the smaller disk is inclined at an angle of 71 degrees.
Each frame shows the dark matter in red, the disk stars in blue, and the bulge stars in yellow. The nominal time-span between frames is 250 million years, or roughly one galactic rotation period.
The main result of this and similar calculations is that disk galaxies can sometimes accrete smaller (1/3-mass) companions without being totally disrupted, in contrast to the outcome of equal-mass mergers. Here the large disk survives because it does not couple strongly to a retrograde perturber.
Computer simulation performed at the Maui High-Performance Computing Center (MHPCC).
Last modified: September 28, 1995