Hickson 40 Galaxy Group

Hickson 40 Galaxy GroupThe Hickson Compact Group 40 is an unusual collection of five galaxies that was chosen to be photographed for the celebration of the 32nd birthday of the Hubble Space Telescope. This compact group includes three spiral shaped galaxies, an elliptical galaxy, and a lenticular (lens like) galaxy that crossed paths in their evolution to create an exceptionally crowded and eclectic galaxy sampler. The galaxies are caught in a leisurely gravitational dance

The Hickson Compact Group 40 is an unusual collection of five galaxies that was chosen to be photographed for the celebration of the 32nd birthday of the Hubble Space Telescope. This compact group includes three spiral-shaped galaxies, an elliptical galaxy, and a lenticular (lens-like) galaxy that crossed paths in their evolution to create an exceptionally crowded and eclectic galaxy sampler. The galaxies are caught in a leisurely gravitational dance and are so crowded that they could fit within a region of space that is less than twice the diameter of our Milky Way's stellar disk.

Despite being in such close proximity, the galaxies in Hickson Compact Group 40 are notably isolated in their own small patch of the universe, in the direction of the constellation Hydra. One possible explanation is that there's a lot of dark matter associated with these galaxies, which can form a big cloud within which the galaxies are orbiting. As the galaxies plow through the dark matter, they feel a resistive force due to its gravitational effects. This slows their motion and makes the galaxies lose energy, so they fall together. Therefore, this snapshot captures the galaxies at a very special moment in their lifetimes, as in about 1 billion years they will eventually collide and merge to form a giant elliptical galaxy.

Astronomers have studied this compact galaxy group in various wavelengths such as visible light, radio, infrared, and X-ray. The observations suggest that the galaxies have been gravitationally interacting due to the presence of a lot of hot gas among the galaxies. The galaxies also have a compact radio source in their cores, which could be evidence for the presence of supermassive black holes. Infrared observations reveal clues to the rate of new star formation.

Hickson Compact Group 40 is one of the most densely packed galaxy groups that have been cataloged in sky surveys going back several decades. Observing galaxies in nearby groups like this help astronomers sort out when and where galaxies assembled themselves, and what they are assembled from. Studying these details helps in understanding how black holes were powered and quasars came into existence.

Image credits: NASA, ESA, STScI Image Processing: Alyssa Pagan (STScI)