 Of course we cannot watch a collision of galaxies unfold, it takes billions of years. But we do see colliding galaxies in various stages of a collision process across the cosmos. The ones we saw are only a few of the hundreds photographed by the Hubble telescope. Later models show us how galaxies of similar sizes might be transformed during a collision. The next six interacting galaxies that I'm going to show you represent various phases in the billion year collision process. This Hubble image displays a beautiful pair of interacting spiral galaxies with swirling arms. A smaller of the two seems to be safe for now, but will probably be swallowed by the larger spiral galaxy eventually. Here we have a pair of very gas-rich spiral galaxies in their early stages of interaction. Here we see the staggering aftermath of an encounter between two galaxies, resulting in a ring-shaped galaxy and a long-tailed companion. The collision between the two parent galaxies produced a shockwave effect that first drew the matter in to the center and then caused it to propagate back outward in a ring. The elongated companion perpendicular to the ring suggests that APR-148 is a unique snapshot of an ongoing collision. This Hubble image is a stunning snapshot of a celestial dance, performed by a pair of similar sized galaxies. Two clear signatures of the gravitational tug of war between the galaxies are one, the bridge of material that connects them, and two, the disruption of their main bodies. The dust lanes between the two galaxy centers show the extent of the distortion to the originally flat disks that have been pulled into three-dimensional shapes. Here we have two galaxies that seem to be embracing each other. Two long, highly curved arms of gas and stars emerge from a center region that has two cores. The two cores are 16,000 light-years apart. The pair is thought to be midway through a merger. This is a beautiful object that resembles an owl in flight. It consists of a pair of former disk galaxies undergoing a collision. The cores of the two individual galaxies, seen at the center of the image, are embedded in hot dust and contain a large number of stars. Two huge wings sweep out from the center and curve in opposite directions. These are tidal tails of stars and gas that have been pulled from the easily distorted disks of the original galaxies. Here's an interesting computer simulation. You'll recognize the last six objects we discussed at key points along the way.