This captivating image from the NASA/ESA Hubble Space Telescope showcases an interacting galaxy trio known as Arp-Madore 2339-661. The Arp-Madore catalog consists of peculiar galaxies, and this particular group is more unusual than it might first appear because it involves not two, but three galaxies in the process of interacting.
The two clearly distinguishable galaxies in this image are NGC 7733 (the smaller one to the lower right) and NGC 7734 (the larger one to the upper left). The third galaxy, currently identified as NGC 7733N, can be found by carefully examining the upper arm of NGC 7733. There, you can see a knot-like structure emitting a different color than the arm and partially hidden by dark dust. While it might seem to be a part of NGC 7733, a closer analysis of its velocity (speed and direction) indicates that this knot has a significant additional redshift.
This suggests that it’s most likely its own separate galaxy, not a part of NGC 7733. The challenge for observational astronomers is to determine whether an astronomical object is a single entity or multiple objects, especially when one appears to be in front of another from Earth’s perspective.
All three galaxies in this image are located in close proximity to each other, roughly 500 million light-years from Earth in the constellation Tucana. As the image portrays, they are in the process of gravitational interaction with one another. Some scientific literature even refers to them as a “merging group,” indicating that they will eventually merge to become a single entity over time through gravitational interactions. This image captures a fascinating stage in the life cycle of these galaxies as they evolve and interact.