A Less Disruptive Galaxy Merger
This galaxy here has an unusual shape. It does not look like a normal spiral galaxy because it has a lot of diffuse reddish light like an elliptical galaxy. But it does not look like an elliptical galaxy either, because it has a rather fluffy stellar disk with a clearly visible dust disk embedded in it. It is also highly asymmetrical, with a large streamer of stars extending to the right.
The asymmetry of this galaxy and the "fluffiness" of its disk suggest that this galaxy has recently collided with another galaxy and swallowed it up. It is likely that collision occurred between and large galaxy and a small galaxy, rather than two of equal size, because the stellar disk of the larger galaxy was not completely destroyed. Merging events between galaxies of equal size tend to be the most disruptive. Still, this disk is considerably thicker and fluffier than the disk of a typical spiral galaxy, so the smaller galaxy couldn't have been too small. Its gravitational pull has perturbed the orbits of the disk stars in the bigger galaxy away from their orderly rotation. During the collision, the smaller galaxy would have been stripped of its stars; these have been added to the diffuse halo of the remnant galaxy.
In several hundred million years, this galaxy will look more settled than it does today and may even appear to be a massive but relatively normal spiral galaxy with a large spheroidal bulge of stars around it. More violent merging events completely disrupt the stellar disks of the galaxies involved, producing an even more chaotic merger remnant, which will eventually settle into looking like an elliptical galaxy.