Galactic "rocket engine" explains unusual stellar motion in galaxies

A discovery by MPIA graduate student Athanasia Tsatsi has changed astronomers' understanding of how mergers of two galaxies can produce unusual stellar motion in the resulting elliptical galaxies, with the central region rotating in the direction opposite to that of the galaxy's other stars. Previously, such differences had been thought to be the result of an opposite ("retrograde") orientation of the galaxies prior to their merger. Looking at a simulation of a galaxy merger, Tsatsi discovered a...