Depicts different phases of the merger of two galaxies with central supermassive black holes, time progressing from left to right.The images show the gas of two colliding spiral galaxies. After the first encounter, they first separate again from each other, but then come together for a second encounter and subsequent coalescence. Gravity is driving gas into the centers of the galaxies, and this inflow results in rapid black hole growth during a "quasar phase". This episode lasts up to 100 million years and releases enough energy to heat the gas and to expel out of the galaxies. Such an event will result in an elliptical galaxy, mostly devoid of gas and hosting at its center the now-merged pair of supermassive black holes.

Methods: GADGET code