A Galaxy Grouping in 2D and 3D: Stephan’s Quintet

In 1877, Edouard Stephan discovered a tight visual grouping of five galaxies located in the constellation Pegasus. The galaxies of Stephan’s Quintet are both overlapping and interacting, and have become the most famous among the compact groups of galaxies. Astronomers have long known that four of the galaxies (all of which are yellowish-white in this video) form a physical group in space, while the fifth (bluish) is a foreground galaxy. In addition, a sixth galaxy (yellowish-white and on the far left) is likely to be part of the physical grouping. Hence, this 2D quintet that is a 3D quartet may actually be a 2D sextet that is a 3D quintet.

This visualization makes apparent the spatial distribution of these galaxies. The video starts with a view that matches our 2D perspective. As the sequence travels in 3D, the foreground blue spiral, NGC 7320, quickly passes by the camera. The possible sixth galaxy member on the left, NGC 7320C, is seen at roughly the same distance as the remaining four galaxies. The camera turns to pass between two strongly interacting galaxies, NGC 7319 (left) and NGC 7318B (right), with each galaxy’s spiral structure distorted by the gravitational interaction. In contrast, NGC 7318B overlaps in 2D with the more distant elliptical NGC 7318A, but does not have a strong interaction. The other elliptical, NGC 7317, is also seen as more distant than the strongly interacting pair. In 3D, the four or five galaxies in this group are gathered together by their mutual gravity, and may collide and merge together in the future.

Credits: G. Bacon, J. DePasquale, F. Summers, Z. Levay (STScI)