This might easily pass as part of NGC 7733, but analysis of the velocities (speed, but likewise considering direction) included in the galaxy reveals that this knot has a significant extra redshift, meaning that it is most likely its own entity and not part of NGC 7733. This is actually among the many obstacles that observational astronomers face: exercising whether an astronomical object actually is just one, or one depending on front of another as seen from Earths point of view!
All three galaxies lie rather near to each other, roughly 500 million light-years from Earth in the constellation Tucana, and, as this image shows, they are connecting gravitationally with one another. In fact, some science literature describes them as a merging group, meaning that they are on a course to ultimately become a single entity.
This Hubble Space Telescope image of Arp-Madore 2339-661 exposes a connecting galaxy pair from the Arp-Madore brochure of peculiar galaxies. A better look uncovers a third galaxy, making it a trio of communicating galaxies.
Arp-Madore 2339-661, initially thought to be a set of interacting galaxies, remains in reality a trio comprising NGC 7733, NGC 7734, and NGC 7733N. Located in the Tucana constellation, they are on course to merge into a single entity.
This striking image from the Hubble Space Telescope records the engaging galaxy set referred to as Arp-Madore 2339-661, so named due to the fact that they come from the Arp-Madore catalog of peculiar galaxies. This particular peculiarity may be even odder than first fulfills the eye, as there are in truth three galaxies connecting here, not simply two..
The two clearly defined galaxies are NGC 7733 (smaller, lower right) and NGC 7734 (bigger, upper left). The third galaxy is presently referred to as NGC 7733N, and can in fact be spotted in this image if you look thoroughly at the upper arm of NGC 7733, where there is a visually significant knot-like structure, radiant with a different color to the arm and obscured by dark dust.
