Snapshots of the time evolution of a collision of two spiral galaxies with black holes at
their center from a computer simulation.
Color indicates temperature and brightness the gas density. When the galaxies and their
black holes collide a quasar is ignited which expels most of the gas in a strong wind. The remaining galaxy contains very little gas but a large supermassive black hole.
The black hole mass and the end is related
to the size of the galaxy in agreement with
observations.

This computer animation visualises the full time evolution of a galaxy collision simulation of two spiral galaxies that host supermassive black holes at their centres. Only the gas distribution in the galaxies is shown. As in the figure, brightness represents gas density while the colour hue indicates gas temperature.