via Astronomy Now.
What happens when a small dense galaxy meets a big spiral galaxy? Well, as we know from the Small and Large Magellanic Clouds, the remnants of satellite galaxies interacting with our own spiral galaxy, they eventually end up coming together as one big disc galaxy. But in the process, the satellites tug and tear at the spiral galaxy in such a way as to leave signature features, which have been observed in galaxies around us – these include rings of stars and the kind of frayed edges that our own galaxy shows.
The recent study was conducted by Stelios Kazantzidis of Ohio State University and colleagues. It showed the importance of using dark matter in models to get the morphology of these interactions correct.