In this model, two disk galaxies collide. Yellow/white shows the stars in the model, while blue shows the interstellar gas. The whole sequence covers approximately one billion years.
Upper Left: The galaxies approach one another,
just before they collide.
Upper Middle: Immediately after collision, the
galaxies become very distorted.
Upper Right: The tidal tails begin to expand away,
as the galaxies move apart.
Lower Left: The galaxies turn around on their
orbit and begin to fall back towards one another, as the tidal tails continue
to expand.
Lower Middle: The galaxies re-collide and merge
into a single object.
Lower Right: The merger remnant settles down after
the collision, while some material from the tidal tails streams back into
the remnant.
Image Credit: Chris Mihos and Sean Maxwell, Case Western Reserve University